5 roughly represent the grids employed for the negative and positive plates respectively of a type used for lighting. Fig. 6 is the cross section of the casting used for the Plante positive of the larger cells for rapid discharge. Finer indentations on the side expose a large surface. Fig. 7 shows a complete cell.
Hart cell.
The Hart cell, as used for lighting, is a combination of the Plante and Faure (pasted) types. The plates hang by side lugs on glass slats, and are separated by three rows of glass tubes 3/8 inch diameter (fig. 8). The tubes rest in grooved teak wood blocks placed at the bottom of the glass boxes. The blocks also serve as base for a skeleton framework of the same material which surrounds and supports the section. Of course the wood has to be specially treated to withstand the acid. A special non-corrosive terminal is used. A coned bolt draws the lug ends of adjacent cells together, fitting in a corresponding tapered hole in the lugs, and thus increasing the contact area. The positive and negative tapers being different, a cell cannot be connected up in the wrong way.
FIG. 8.—Hart Accumulator.
Gould cell.
In America, in addition to some of the cells already described, there are types which are not found in England. Two may be described. The Gould cell is of the Plante type. A special effort is made to reduce local and other deleterious action by starting with perfectly homogeneous plates. They are formed from sheet lead blanks by suitable machines, which gradually raise the surface into a series of ribs and grooves. The sides and middle of the blank are left untouched and amply suffice to distribute the current over the surface of the plate. The grooves are very fine, and when the active material is formed in them by electro-chemical action, they hold it very securely.
Hatch cell.
The Hatch cell has its positive enclosed in an envelope. A very shallow porous tray (made of kaolin and silica) is filled with red lead paste, an electrode of rolled sheet lead is placed on its surface, and over this again is placed a second porous tray filled with paste. The whole then looks like a thin earthenware box with the lug of the electrode projecting from one end. The negatives consist of sheet lead covered by active material. On assembling the plates, each negative is held between two positive ``boxes,'' the outsides of which have protecting vertical ribs. These press against the active material on the negative plates, and help to keep it in position. At the same time, the clearance between the ribs allows room for acid to circulate freely between the negative plate and the outer face of the positive envelope. Diffusion of the acid through this envelope is easy, as it is very porous and not more than 1/32 inch thick.
Traction Cells.—-Attempts to run tramcars by accumulators have practically all failed, but traction cells are employed for electric broughams and light vehicles for use in towns. There are no large deviations in manufacture except those imposed by limited space, weight and vibration. The plates are generally thinner and placed closer together. The Plante positive is not used so much as in lighting types. The acid is generally a little stronger in order to get a higher electromotive force (E.M.F.). To prevent the active material from being shaken out of the grids, corrugated and perforated ebonite separators are placed between the plates. The ``chloride'' traction cell uses a special variety of wood separator: the ``exide'' type of plate is used for both positive and negative. Cells are now made to run 3000 or more miles before becoming useless. The specific output can be made as high as 10 or 11 watt-hours per pound of cell, but this involves a chance of shorter life. The average working requirement for heavy vehicles is about 50 watt-hours per 1000 lb. per mile.
Ignition Cells for motor cars are made on the same lines as traction cells, though of smaller capacity. As a rule two cells are put up in ebonite or celluloid boxes and joined in series so as to give a 4-volt battery, the pressure for which sparking coils are generally designed. The capacity ranges from 20 to 100 ampere-hours, and the current for a single cylinder engine will average one to one and a half amperes during the running intervals.
General Features.—The tendency in stationary cells is to allow plenty of space below the plates, so that any active material which falls from the plates may collect there without risk of short-circuit, &c. More space is allowed between the plates, which means that (a) there is more acid within reach, and (b) a slight buckling is not so dangerous, and indeed is not so likely to occur. The plates are now generally made thicker than formerly, so as to secure greater mechanical rigidity. At the same time, the manufacturers aim at getting the active materials in as porous a state as possible.
The figures with regard to specific output are difficult to classify. It would be most interesting to give the data in the form of watt-hours per pound of active material, and then to compare them with the theoretical values, but such figures are impossible in the nature of the case except in very special instances. For many purposes, long life and trustworthiness are more important than specific output. Except in the case of traction cells, therefore, the makers have not striven to reduce weight to its lowest values. Table I. shows roughly the weight of given types of cells for a given output in ampere hours.
TABLE I.Capacity in ampere-hours ifType of cell. discharged in Weight of cell.9 hrs. 6 hrs. 3 hrs. 1 hr.Ordinary light-ing . . . . . 200 182 153 101 100 pounds'' '' 420 380 300 210 200 pounds'' '' 1200 1080 880 600 670 poundsCentral stationand High Rate 3500 3100 2500 1700 2000 pounds'' '' 6000 5400 4400 3000 3200 poundsTraction . . . 220 185 155 125 40 pounds'' . . . .. 440 .. .. 90 pounds
Influence of Temperature on Capacity.—-These figures are true only at ordinary temperatures. In winter the capacity is diminished, in summer it is increased. The differences are due partly to change of liquid resistance but more especially to the difference in the rate at which acid can diffuse into or out of the pores: obviously this is greater at higher temperatures. The increase in capacity on warming is appreciable, and may amount to as much as 3% per degree centigrade (Gladstone and Hibbert, Journ. Inst. Elec. Eng. xxi. 441; Helm, Electrician, NOV. 1901, i. 55; Liagre, L'Eclairage electrique, 1901,xxix. 150). Notwithstanding these results, it is not advisable to warm accumulators appreciably. At higher temperatures, local action is greatly increased and deterioration becomes more rapid. It is well, however, to avoid low winter temperatures.
Working of accumulators.—Whatever the type of cell may be, it is important to attend to the following working requirements—(1) The cells must be fully equal to the maximum demand, both in discharge rate and capacity. (2) All the cells in one series ought to be equal in discharge rate and capacity. This involves similarity of treatment. (3) The cells are erected on strong wooden stands. Where floor space is too expensive, they can be erected in tiers; but, if possible, this should be avoided. They ought to lie in rows, so arranged that it is easy to get to one side (at least) of every cell, for examination and testing, and if need be to detach and remove it or its plates. Where a second tier is plaeed over the first, sufficient clearance space must be allowed for the plates to be lifted out of the lower boxes. The cells are insulated by supporting them on glass or mushroom-shaped oil insulators. If the containing vessels are made of glass, it it desirable to put them in wooden trays which distribute the weight between the vessel and insulators. To prevent acid spray from filling the air of the room, a glass plate is arranged over each cell. The positive and negative sections are fixed in position with insulating forks or tubes, and the positive terminal of one cell is joined to the negative of the next by burning or bolting. If the latter method is adopted, the surfaces ought to be very clean and well pressed home. The joint ought to be covered by vaseline or varnish. When this has been done, examination ought to be made of each cell to see that the plates are evenly spaced, that the separators (glass tubes or ebonite forks between the plates) are in position and vertical, and that there are no scales or other adventitious matter connecting the plates. The floor of the cell ought to be quite clear; if anything lies there it must be removed. (4) To mix the solution a gentle stream of sulphuric acid must be poured into the water (not the other way, lest too great heating cause an accident). It is necessary to stir the whole as the mixing proceeds and to arrange that the density is about 1190, or according to the recommendation of the maker. About five volumes of water ought to be taken to one volume of acid. After mixing, allow to cool for two or three hours. The strong acid ought to be free from arsenic, copper and other similar impurities. The water ought to be as pure as can be obtained, distilled water being best; rain water is also good. If potable water be employed, it will generally be improved by boiling, which removes some of the lime held in solution. The impurity in ordinary drinking water is very slight; but as all cells lose by evaporation and require additions of water from time to time, there is a tendency for it to increase. The acid must not be put into the cells till everything is ready for charging. (5) A shunt-wound or separately-excited dynamo being ready and running so as to give at will 2.6 or 2.7 volts per cell, the acid is run into the cells. As soon as this is done, the dynamo must be switched on and charging commenced. The positive terminal of the dynamo must be joined to the positive terminal of the battery. If necessary, the + end of the machine must be found by a trial cell made of two plain lead sheets in dilute acid. It is important also to maintain this first charging operation for a long time without a break. Twelve hours is a minimum time, twenty-four not too much. The charging is not even then complete, though a short interval is not so injurious as in the earlier stage. The full charge required varies with the cells, but in all types a full and practically continuous first charge is imperatively necessary. During the early part of this charge the density of the acid may fall; but after a time ought to increase, and finally reach the value desired for permanent working. Towards the end of the ``formation'' vigilant observation must be exercised. It is important to notice whether any cells are appreciably behind the others in voltage, density or gassing. Such cells may be faulty, and in any case they must be charged and tended till their condition is like that of the others. They ought not to go on the discharge circuit till this is assured. The examination of the cells before passing them as ready for discharge includes:—-(a) Density of acid as shown by the hydrometer. (b) Voltage. This may be taken when charging or when idle. In the first case it ought to be from 2.4 to 2.6 volts, according to conditions. In the second ease it ought to be just over 2 volts, provided that the observation is not taken too soon after switching in the charging current. For about half an hour after that is done, the E.M.F. has a transient high value, so that, if it be desired to get the proper E.M.F. of the cell, the observation must be taken thirty minutes after the charging ceases.
(c) Eye observations of the plates and the acid between them. The positive plates ought to show a rich dark brown colour, the negatives a dull slate-blue, and the space between ought to be quite clear and free from anything like solid matter. All the positives ought to be alike, and similarly all the negatives. If the cells show similarity in these respects they will probably be in good working order.
As to management, it is important to keep to certain simple rules, of which these are the chief:—(1) Never discharge below a potential difference of 1.85 (or in rapid discharge, 1.8) volt. (2) Never leave the cells discharged, if it be avoidable. (3) Give the cells a special full charging once a month. (4) Make a periodic examination of each cell, determining its E.M.F., density of acid, the condition of its plates and freedom from growth. Any incipient growth, however small, must be carefully watched. (5) If any cell shows signs of weakness, keep it off discharge till it has been brought back to full condition. See that it is free from any connexion between the plates which would cause short-circuiting; tne frame or support which carries the plates sometimes gets covered by a conducting layer. To restore the cell, two methods can be adopted. In private installations it may be disconnected and charged by one or two cells reserved for the purpose; or, as is preferable, it may be left in circuit, and a cell in good order put in parallel with it. This acts as a ``milking'' cell, not only preventing the faulty one from discharging, but keeping it supplied mith a charging current till its potential difference (P.D.) is normal. Every battery attendant should be provided with a hydrometer and a voltmeter. The former enables him to determine from time to time the density of the acid in the cells; instruments specially constructed for the purpose are now easily procurable, and it is desirable that one be provided for every 20 or 25 cells. The voltmeter should read up to about 3 volts and be fitted with a suitable connector to enable contacts to be made quickly with any desired cell. A portable glow lamp should also be available, so that a full light can be thrown into any cell; a frosted bulb is rather better than a clear one for this purpose. He must also have some form of wooden scraper to remove any growth from the plates. The scraping must be done gently, with as little other disturbance as possible. By the ordinary operations which go on in the cell, small portions of the plates become detached. It is important that these should fall below the plates, lest they short-circuit the cell, and therefore sufficient space ought to be left between the bottom of the plates and the floor of the cell for these ``scalings'' to accumulate without touching the plates. It is desirable that they be disturbed as little as possible till their increase seriously encroaches on the free space. It sometimes happens that brass nuts or bolts, &c., are dropped into a cell; these should be removed at once, as their partial solution would greatly endanger the negative plates. The level of the liquid must be kept above the top of the plates. Experience shows the advisability of using distilled water for this purpose. It may sometimes be necessary to replenish the solution with some dilute acid, but strong acid must never be added.
The chief faults are buckling, growth, sulphating and disintegration. Buckling of the plates generally follows excessive discharge, caused by abnormal load or by accidental short-circuiting. At such times asymmetry in the cell is apt to make some part of the plate take much more than its share of the current. That part then expands unduly, as explained later, and curvature is produced. The only remedy is to remove the plate, and press it back into shape as gently as possible. Growth arises generally from scales from one part falling on some other—say, on the negative. In the next charging the scale is reduced to a projecting bit of lead, which grows still further because other particles rest on it. The remedy is, gently to scrape off any incipient growth. Sulphating, the formation of a white hard surface on the active material, is due to neglect or excessive discharge. It often yields if a small quantity of sulphate of soda be added to the liquid in the cell. Disintegration is due to local action, and there is no ultimate remedy. The end can be deferred by care in working, and by avoiding strains and excessive discharge as much as possible.
Accumulators in repose.—-Accumulators contain only three active substances—-spongy lead on the negative plate, spongy lead peroxide on the positive, and dilute sulphuric acid between
Substance. Colour. Density. Specific Resistance.Lead . . . . slate blue 11.3 0.0000195 ohmPeroxide of lead dark brown 9.28 5.6 to 6.8 ''Sulphuric acidafter charge clear liquid 1.210 1.37 ''Sulphuric acidafter discharge '' '' 1.170 1.28 ''Sulphuric acid belowin pores . . . '' '' 1.03 8.0 ''Sulphate of lead white 6.3 non-conductor.
them. Sulphate of lead is formed on both plates during discharge and brought back to lead and lead peroxide again during charge, and there is a consequent change in the strength of acid during every cycle. The chief properties of these substances are shown in Table II.
The curve in fig. 9 shows the relative conductivity (reciprocal of resistance) of all the strengths of sulphuric acid solutions, and by its aid and the figures in the preceding table, the specific resistance of any given strength can be determined.
Fig 9 The lead accumulator is subject to three kinds of local action. First and chiefly, local action on the positive plate, because of the contact between lead peroxide and the lead grid which supports it. In carelessly made or roughly handled cells this may be a very serious matter. It would be so, in all circumstances if the lead sulphate formed on the exposed lead grid did not act as a covering for it. It explains why Plante found ``repose'' a useful help in ``forming,'' and also why positive plates slowly disintegrate; the lead support is gradually eaten through. Secondly, local action on the negative plate when a more electro-negative metal settles on the lead. This often arises when the original paste or acid contains metallic impurities. Similar impurity is also introduced by scraping copper wire, &c., near a battery. Thirdly, local action due to the acid varying in strength in different parts of a plate. This may arise on either plate and is set up because two specimens of either the same lead or the same peroxide give an E.M.F. when placed in acids of different strengths. J. H. Gladstone and W. Hibbert found that the E.M.F. depends on the difference of strength. With two head plates, a maximum of about quarter volt was obtained, the lead in the weaker acid being positive. With two peroxide plates the maximum voltage was about 0.64, the plate in stronger acid being positive to that in weaker. The electromotive force
FIG. 10. of a cell depends chiefly on the strength of the acid, as may be seen from fig. 10 taken from Gladstone and Hibbert's paper (Journ. Inst. Elec. Eng., 1892).The observations with very strong acid were difficult to obtain, though even that with 98% acid marked X is believed to be trustworthy. C. Heim (Elek. Zeit, 1889), F. Streintz (Ann. Phys. Chem. xlvi. p. 449) and F. Dolezalek (Theory of Lead Accumulators, p. 55) have also given tables.
It is only necessary to add to these results the facts illustrated by the following diffusion curves, in order to get a complete clue to the behaviour of an accumulator in active work. Fig. 11 shows the rate of diffusion from plates soaked in 1.175 acid and then placed in distilled water. It is from a paper by L. Duncan and H. Wiegand (Elec. World, N.Y., 1889), who were the first to show the importance of diffusion. About one half the acid diffused out in 30 minutes, a good illustration of the slowness of this process. The rate of diffusion is much the same for both positive and negative plates; but slower for discharged plates than for charged ones. Discharge affects the rate of diffusion on the lead plate more than on the peroxide plate. This is in accordance with the density values given in Table I. For while lead sulphate is formed in the pores of both plates, the consequent expansions (and obstructions) are different; 100 volumes of lead form 290 volumes of sulphate (a threefold
expansion), and 100 volumes of peroxide form 186 volumes of sulphate (a twofold expansion). The influence of diffusion on the electromotive force is illustrated by fig. 12. A cell was prepared with 20% acid. It also held a porous pot containing stronger acid, and into this the positive plate was suddenly transferred from the general body of liquid. The E.M.F. rose by diffusion of stronger acid into the pores. Curve I. in fig. 12 shows the rate of rise when the porous pot contained 34% acid; curve II. was obtained with the stronger (58%) acid (Gladstone and Hibbert, Phil. Mag., 1890). Of these two curves the first is more useful, because its conditions are nearer those which occur in practice.
At the end of a discharge it is a common thing for the plates to be standing in 25% acid, while inside the pores the acid may not exceed 8% or 10%. If the discharge be stopped, we have conditions somewhat like fig. 12, and the E.M.F. begins to rise. In one minute it has gone up by about 0.08 volt, &c.
Fig. 12.
Charge and Discharge.—-The most important practical questions concerning an accumulator are:—its maximum rate of working; its capacity at various discharge rates; its efficiency; and its length of life. Apart from mechanical injury all these depend primarily on the way the cell is made, and then on the method of charging and discharging. For each type and size of cell there is a normal maximum discharging current. Up to this limit any current may be taken; beyond it, the cell may suffer if discharge be continued for any appreciable time. The most important point to attend to is the voltage at which discharge shall cease. The potential difference at terminals must not fall below 1.80 volt during discharge at ordinary rates (10 hours) or 1.75 to 1.70 volt for 1 or 2 hour rate. The reason underlying the figures is simple. These voltages indicate that the acid in the pores is not being renewed fast enough, and that if the discharge continue the chemical action will change: sulphate will not be formed in situ for want of acid. Any such change in action is fatal to reversibility and therefore to life and constancy in capacity. To illustrate: when at slow discharge rates the voltage is 1.80 volt, the acid in the pores has weakened to a mean value of about 2.5% (see fig. 11), which is quite consistent with some part of the interior being practically pure water. With high discharge rates, something like 0.1 volt may be lost in the cells, by ordinary ohmic fall, so that a voltage reading of 1.73 means an E.M.F. of a little over 1.8 volt, and a very weak density of the acid inside the pores. Guided by these figures, an engineer can determine what ought to be the permissible drop in terminal volts for any given working conditions. Messrs W. E. Ayrton, C. G. Lamb, E. W. Smith and M. W. Woods were the first to trace the working of a cell through varied conditions (Journ. Inst. Elec. Eng., 1890), and a brief resume of their results is given below.
They began by charging and discharging between the limits of 2.4 and 1.6 volts.
Fig. 13 shows a typical discharge curve. Noteworthy points are:—(1) At the beginning and at the end there is a rapid fall in P.D., with an intermediate period of fairly uniform value. (2) When the
Fig. 13.
P.D. reaches 1.6 volt the fall is so rapid that there is no advantage in continuing the action. When the P.D. had fallen to 1.6 volt the cell was automatically switched into a charging circuit, and with a current of 9 amperes yielded the curve in fig. 14. Here again there is a rapid variation in P.D. (in these cases a rise) at the beginning and end of the operation. The cells were now carried through the same cycle several times, giving almost identical values for each cycle. After some days, however, they became more and more difficult to charge, and the return on discharge was proportionately less. It became impossible to charge up to a P.D. of 2.4 volts, and finally the capacity fell away to half its first value. Examination showed that the plates were badly scaled, and that some of the scales had partially connected the plates. These scales were cleared away and the experiments resumed, limiting the fall of P.D. to 1.8 volt. The
Fig. 14.
difficulties then disappeared, showing that discharge to 1.6 volt caused injury that did not arise at a limit of 1.8. Before describing the new results it will be useful to examine these two cases in the light of the theory of E.M.F. already given.
(a) Fall in E.M.F. at beginning of discharge.—At the moment when previous charging ceases the pores of the positive plate contain strong acid, brought there by the charging current. There is consequently a high E.M.F. But the strong acid begins to diffuse away at once and the E.M.F. falls rapidly. Even if the cell were not discharged this fall would occur, and if it were allowed to rest for thirty minutes or so the discharge would have begun with the dotted line (fig. 13). (b) Final rapid fall.—-The pores being clogged by sulphate the plugs cannot get acid by diffusion, and when 5% is reached the fall in E.M.F. is disproportionately large (see fig. 10). If discharge be stopped, there is an almost instantaneous diffusion inwards and a rapid rise in E.M.F. (c) The rise in E.M.F. at beginning and end of the charging is due to acid in the pores being strengthened, partly by diffusion, partly by formation of sulphuric acid from sulphate, and partly by electrolytic carrying of strong acid to the positive plate. The injurious results at 1.6 volt arise because then the pores contain water. The chemical reaction is altered, oxide or hydrate is formed, which will partially dissolve, to be changed to sulphate when the sulphuric acid subsequently diffuses in. But formed in this way it will not appear mixed with the active masses in the electrolytic paths, but more or less alone in the pores. In this position it will more or less block the passage and isolate some of the peroxide. Further, when forming in the narrow passage its disruptive action will tend to force off the outer layers. It is evident that limitation of P.D. to 1.8 volt ought to prevent these injuries, because it prevents exhaustion of acid in the plugs.
Fig. 15 shows the results obtained by study of successive periods of rest, the observations being taken between the limits of 2.4 and 1.8 volts. Curves A and B show the state and capacity at the beginning. After a 10 days' rest the capacity was smaller, but repeated cycles
Fig. 15.
of work brought it back to C and D. A second rest (10 days), followed by many cycles, then gave E and F. After a third rest (16 days) and many cycles, G and H were obtained. After a fourth rest (16 days) the first discharge gave I and the first charge J. Repeated cycles brought the cells back to K and L. Curves M and N show first cycle after a fifth rest (16 days); O and P show the final restoration brought about by repeated cycles of work. The numbers given by the integration of some of these curves are stated in Table III.
Capacity and Efficiency under VariousConditions of Working.Discharge. Charge. Efficiency.Experiment. Ampere- Watt Ampere- Watt Quan- Energy.hours. hours. hours. hours. tity.——————————————————————————————————Normal cycle 102 201.7 104.5 230.7 97.2 87.4Restorationafter 1st rest 100 179 103.8 228.2 96.8 85.8Restorationafter 2nd rest 91 176.7 103.8 228.2 96.8 85.8Restorationafter 3rd rest 82.6 161.3 86.2 190.5 95.8 84.7Dischargeimmediately 56.5 110.5 86.2 190.5 65.5 581after rest . 56.5 110.5 71.1 158.3 79.6 69.6Restorationafter 8 cycles 80 156.9 83.8 184.6 95.5 85————————————————————————————————————
The table shows that the efficiency in a normal cycle may be as high as 87.4%; that during a rest of sixteen days the charged
1 This discharge is here compared with the charge that preceded the rest; in the next line the same discharge is compared with the charge following the rest.
accumulator is so affected that about 30% of its charge is not available, and in subsequent cycles it shows a diminished capacity and efficiency; and that by repeated charges and discharges the capacity may be partially restored and the efficiency more completely so. These changes might be due to—(a) leakage or short-circuit, (b) some of the active material having fallen to the bottom of the cell or (c) some change in the active materials. (a) is excluded by the fact that the subsequent charge is smaller, and (b) by the continued increase of capacity during the cycles that follow the rest. Hence the third hypothesis is the one which must be relied upon. The change in the active materials has already been given. The formation of
lead sulphate by local action on the peroxide plate and by diract action of acid on spongy metal on the lead plate explains the loss of energy shown in curve M, fig. 15, while the fact that it is probably formed, not in the path of the regular currents, but on the wall of the grid (remote from the ordinary action), gives a probable explanation of the subsequent slow recovery. The action of the acid on the lead during rest must not be overlooked.
We have seen that capacity diminishes as the discharge rate increases; that is, the available output increases as the current diminishes. R. E. B. Crompton's diagram illustrating this fact is given in fig. 16. At the higher rates the consumption of acid is too rapid, diffusion cannot maintain its strength in the pores, and the fall comes so much earlier.
The resistance varies with the condition of the cell, as shown by the curves in fig. 17. It may be unduly increased by long or narrow lugs, and especially by dirty joints between the lugs. It is interesting to note that it increases at the end of both charge and discharge, and
Fig. 17.
much more for the first than the second. Now the composition of the active materials near the end of charge is almost exactly the same as at the beginning of discharge, and at first sight there seems nothing to account for the great fall in resistance from 0.0115 to 0.004 ohm; that is, to about one-third the value. There is, however, one difference between charging and discharging—-namely, that due to the strong acid near the positive, with a corresponding weaker acid near the negative electrode. The curve of conductivity for sulphuric acid shows that both strong and weak acid have much higher resistances than the liquid usually employed in accumulators, and it is therefore reasonable to suppose that local variations in strength of acid cause the changes in resistance. That these are not due to the constitution of the plugs is shown by the fact that, while the plugs are almost identical at end of discharge and beginning of charge, the resistance falls from 0.0055 to 0.0033 ohm.
While a current flows through a cell, heat is produced at the rate of C2RX0.24 calories (water-gram-degree) per second. As a consequence the temperature tends to rise. But the change of temperature actually observed is much greater during charge, and much less during discharge, than the foregoing expression would suggest; and it is evident that, besdies the heat produced according to Joule's law, there are other actions which warm the cell during charge and cool it during discharge. Duncan and Wiegand loc. cit.), who first observed the thermal changes, ascribe the chief influence to the electrochemical addition of H2SO4 to the liquid during charge and its removal during discharge. Fig. 18 gives some results obtained by Ayrton, Lamb, &c. This elevation of temperature (due to electrolytic strengthening of acid and local action) is a measure of the energy lost in a cycle, and ought to be minimized as much as possible.
Fig. 18.
Chemistry.—-The chemical theory adopted in the foregoing pages is very simple. It declares that sulphate of lead is formed on both plates during discharge, the chemical action being reversed in charging. The following equations express the experimental results.
Condition before
+ plate Liquid - platex. PbO2 + y. H2SO4 + z. Pbn. H2O
After
+ plate Liquid - plate(x-p). PbO2 (y-2p). H2SO4 (z-p). Pb{ }+{ }+{p. PbSO4 (n+2p). H2O p. PbSO4
During charge, the substances are restored to their original condition: the equation is therefore reversed. An equation of this general nature was published by Gladstone and Tribe in 1882, when Oley first suggested the ``sulphate', theory, which was based on very numerous analyses. Confirmation was given by E. Frankland in 1883, E. Reynier 1884, A. P. P. Crova and P. Garbe 1885, C. Heim and W. F. Kohlrausch 1889, W. E. Ayrton, &c., with G. H. Robertson 1890, C. H. J. B. Liebenow 1897, F. Dolezalek 1897, and M. Mugdan 1899. Yet there has been, as Dolezalek says, an incomprehensible unwillingness to accept the theory, though no suggested alternative could offer good verifiable experimental foundation. Those who seek a full discussion will find it in Dolezalek's Theory of the Lead Accumulator. We shall take it that the sulphate theory is proved, and apply it to the conditions of charge and discharge.
From the chemical theory it will be obvious that the acid in the pores of both plates will be stronger during charge than that outside. During discharge the reverse will be the case. Fig. 19 shows a curve
Fig. 19.
of potential difference during charge, with others showing the concurrent changes in the percentage of PbO2 and the density of acid. These increase almost in proportion to the duration of the current, and indicate the decomposition of sulphate and liberation of sulphuric acid. There are breaks in the P.D. curve at A, B, C, D where the current was stopped to extract samples for analysis, &c. The fall in E.M.F. in this short interval is noteworthy; it arises from the diffusion of stronger acid out of the pores. The final rise of pressure is due to increase in resistance and the effect of stronger acid in the pores, this last arising partly from reduced sulphate and partly from the electrolytic convection of SO4 (see also Dolezalek, Theory, p. 113) . Fig. 20 gives the data for discharge. The percentage of PbO2 and the density here fall almost in proportion to the duration of the current. The special feature is the rapid fall of voltage at the end.
Several suggestions have been made about this phenomenon. The writer holds that it is due to the exhaustion of the acid in the pores. Plante, and afterwards Gladstone and Tribe, found a possible cause in the formation of a film of peroxide on the spongy lead. E. J. Wade has suggested a sudden readjustment of the spongy mass into a complex sulphate. To rebut these hypotheses it is only necessary to say that the fall can be deferred for a long time by pressing fresh acid into the pores hydrostatically (see Liebenow, Zeits. fur Elektrochem., 1897, iv. 61), or by working at a higher temperature. This increases the diffusion inwards of strong acid, and like the increase due to hydrostatic pressure maintains the E.M.F. The other suggested causes of the fall therefore fail. Fig. 20 also shows that when the discharge current was stopped at points A, B, C, D to extract samples, the voltage immediately rose, owing to inward diffusion of stronger acid. The inward diffusion of fresh acid also accounts for the recuperation found after a rest which follows either complete discharge or a partial discharge at a very rapid rate. If the discharge be complete the recuperation refers only to the electromotive force; the pressure falls at once on closed circuit. If discharge has been rapid, a rest will enable the cell to resume work because it brings fresh acid into the active regions.
Fig. 20.
As to the effect of repose on a charged cell, Gladstone and Tribe's experiments showed that peroxide of lead lying on its lead supoort suffers from a local action, which reduces one molecule of PbO2 to sulphate at the same time that an atom of the grid below it is also changed to sulphate. There is thus not only a loss of the available peroxide, but a corrosion of the grid or plate. It is through this action that the supports gradually give way. On the negative plate an action arises between the finely divided lead and the sulphuric acid, with the result that hydrogen is set free— Pb + H2SO4 = PbSO4 + H2. This involves a diminution of available spongy lead, or loss of capacity, occasionally with serious consequences. The capacity of the lead plate is reduced absolutely, of course, but its relative value is more seriously affected. In the discharge it gets sulphated too much, because the better positive keeps up the E.M.F. too long. In the succeeding charge, the positive is fully charged before the negative, and the differences between them tend to increase in each cycle.
Kelvin and Helmholtz have shown that the E.M.F. of a voltaic cell oan be calculated from the energy developed by the chemical action. For a dyad gram equivalent (= 2 grams of hydrogen, 207 grams of lead, &c.), the equation connecting them is E = H/46000 + T dE/dT, here E is the E.M.F. in volts, H is the heat developed by a dyad equivalent of the reacting substances, T is the absolute temperature, and dE/dT is the temperature coefficient of the E.M.F. If the E.M.F. does not change with temperature, the second term is zero. The thermal values for the various substances formed and decomposed are -For PbO2, 62400; for PbSO4, 216210; for H2SO4, 192920; and for H2O, 68400 calories. Writing the equation in its simplest form for strong acid, and ignoring the temperature coefficient term,
PbO2 + 2 H2SO4 + Pb = 2PbSO4 + 2 H2O -62440 - 385840 + 432420 + 136720 leaving a balance of 120860 calories. Dividing by 46000 gives 2.627 volts. The experimental value in strong acid, according to Gladstone and Hibbert, is 2.607 volts, a very close approximation. For other strengths of acid, the energy will be less by the quantity of heat evolved by dilution of the acid, because the chemical action must take the H2SO4 from the diluted liquid. The dotted curve in fig. 10 indicates the calculated E.M.F. at various points when this is taken into account. The difference between it and the continuous curve must, if the chemical theory be correct, depend on the second term in the equation. The figure shows that the observed E.M.F. is above the theoretical for all strengths from 100 down to 5%. Below 5 the position is reversed. The question remains, Can the temperature coefficient be obtained? This is difficult, because the value is so small, and it is not easy to secure a good cycle of observations. Streintz has given the following values:— E 1.9223 1.9828 2.0031 2.0084 2.0105 2.078 2.2070 dE/dT.106 140 228 335 285 255 130 73 Unpublished experiments by the writer give dE/dT. 106 = 350 for anid of density 1.156. With stronger acid, a true cycle could not be obtained. Taking Streintz's value, 335 for 25% acid, the second term of the equation is TdE/dT = 290 X .000335 = 0.0971 volt. The first term gives 88800 calories = 1.9304 volt. Adding the second term, 1.9304 + 0.0971 = 2.2075 volts. The observed value is 2.030 volts (see fig. 10), a remarkably good agreement. This calculation and the general relation shown in fig. 10 render it highly probable that, if the temperature coefficient were known for all strengths of acid, the result would be equally good. It is worth observing that the reversal of relationship between the observed and calculated curves, which takes place at 5% or 6%, suggests that the chemistry must be on the point of altering as the acid gets weak, a conclusion which has been already arrived at on purely chemical grounds. The thermodynamical relations are thus seen to confirm very strongly the chemical and physical analyses.1
Accumulators in Central Stations.—-As the efficiency of accumulators is not generally higher than 75%, and machines must be used to charge them, it is not directly economical to use cells alone for public supply. Yet they play an important and an increasing part in public work, because they help to maintain a constant voltage on the mains, and can be used to distribute the load on the running machinery over a much greater fraction of the day. Used in parallel with the dynamo, they quickly yield current when the load increases, and immediately begin to charge when the load diminishes, thus largely reducing the fluctuating stress on dynamo and engine for sudden variations in load. Their use is advantageous if they can be charged and discharged at a time when the steam plant would otherwise be working at an uneconomical load.
Fig. 21.
Regulation of the potential difference is managed in various ways. More cells may be thrown in as the discharge proceeds, and taken out during charge; but this method often leads to trouble, as some cells get unduly discharged, and the unity of the battery is disturbed. Sometimes the number of cells is kept fixed for supply, but the P.D. they put on the mains is reduced during charge by employing regulating cells in opposition. Both these plans have proved unsatisfactory, and the battery is now preferably joined across the mains in parallel with the dynamo. The cells take the peaks of the load and thus relieve the dynamo and engine of sudden changes, as shown in fig. 21. Here the line current (shown by the erratic curve) varied spasmodically from 0 to 375 amperes, yet the dynamo current varied from 100 to 150 amperes only (see line A). At the same time the line voltage (535 volts normal) was kept nearly constant. In the late evening the cells became exhausted and the dynamo charged them. Extra voltage was required at the end of a ``charge,' and was provided by a ``booster.'' Originally a booster was an auxiliary dynamo worked in series with the chief machine, and driven in any convenient way. It has
1 For the discussion of later electrolytic theories as apolied to accumulators, see Dolezalek, Theory of the Lead Accumulator.
developed into a machine with two or more exciting coils, and having its armature in series with the cells (see fig. 22). The exciting coils act in opposition; the one carrying the main current sets up an E.M.F. in the same direction as that of the cells, and helps the cells to discharge as the load rises. When the load is small, the voltage on the mains is highest and the shunt exciting current greatest. The booster E.M.F. now acts with the dynamo and against the cells, and causes them to take a full charge. Even this arrangement did not suffice to keep the line voltage as constant as seemed desirable in some cases, as where lighting and traction work were put on the same plant. Fig. 23 is a diagram of a complex booster which gives very good regulation. The booster B has its armature in series with the accumulators A, and is kept running in a given direction at a constant speed by means of a shunt-wound motor (not shown), so that the E.M.F. induced in the armature depends on the excitation. This is made
Fig. 22. to vary in value and in direction by means of four independent enciting coils, C1, C2, C3, C4. The last is not essential, as it merely compensates for the small voltage drop in the armature. It is obvious that the excitation C3 will be proportionate to the difference in voltage between the battery and the mains, and it is arranged that battery volts and booster volts shall equal the volts on the mains. Under this excitation there is no tendency for the battery to charge or discharge. But any additional excitation leads to strong currents one way or the other. Excitation C1 rises with the load on the line, and gives an E.M.F. helping the battery to discharge most when the load is greatest. C2 is dependent on the bus-bar voltage, and is greatest when the generator load is small: it opposes C1 and therefore excites the booster to charge the battery. The exact generator load at which the booster shall reverse its E.M.F. from a charging to a discharging value is adjusted by the resistance R2 in series with C2. A similar resistance R6 allows the excitation of C3 to be adjusted. Very remarkable regulation can be obtained by reversible boosters of this type. In traction and lighting stations it is quite possible to keep the variation of bus-bar pressure within 2% of the normal value, although the load may momentarily vary from a few amperes up to 200 or 300.
J. B. Entz has introduced an auxiliary device which enables him to use a much more simple booster. The Entz booster has no series coil and only one shunt coil, the direction and value of excitation due to this being controlled by a carbon regulator, it having two arms, the resistance of each of which can be varied by pressure due to the magnet- izing action of a solenoid. The main current from the generator passes through the solenoid and causes one or other of the two carbon arms to have the less
resistance. This change in resistance determines the direction of the exciter field current, and therefore the direction of the boost. A photograph of the switchboard at Greenock where this booster is in use shows the voltmeter needle as if it had been held rigid, although the exposure lasted 90 minutes. On the same photograph the ammeter needle does not appear, its incessant and large movements preventing any picture from being formed.
Alkaline Accumulators.—Owing to the high electro-chemical equivalent of lead, a great saving in weight would be secured by using almost any other metal. Unfortunately no other metal and its compounds can resist the acid. Hence inventors have been incited to try alkaline liquids as electrolytes. Many attempts have been made to construct accumulators in this way, though with only moderate success. The Lalande-Chaperon, Desmazures, Waddell-Ent2 and Edison are the chief cells. T. A. Edison's cell has been most developed, and is intended for traction work. He made the plates of very thin sheets of nickel-plated steel, in each of which 24 rectangular holes were stamped, leaving a mere framework of the metal. Shallow rectangular pockets of perforated nickel-steel were fitted in the holes and then burred over the framework by high pressures. The pockets contained the active material. On the positive plate this consisted of nickel peroxide mixed with flake graphite, and on the negative plate of finely divided iron mixed with graphite. Both kinds of active material were prepared in a special way. The graphite gives greater conductivity. The liquid was a 20% solution of caustic potash. During discharge the iron was oxidized, and the nickel reduced to a lower state of oxidation. This change was reversed during charge. Fig. 24 shows the general features.
Fig. 24.—Edison Accumulator.
The chief results obtained by European experts showed that the E.M.F. was 1.33 volt, with a transient higher value following charge. A cell weighing 17.8 lb. had a resistance of 0.0013 ohm, and an output at 60 amperes of 210 watt-hours, or at 120 amperes of 177 watt-hours. Another and improved cell weighiog 12.7 lb. gave 14.6 watt-hours per pound of cell at a 20-ampere rate, and 13.5 watt-hours per pound at a 60 ampere rate. The cell could be charged and discharged at almost any rate. A full charge could be given in 1 hour, and it would stand a discharge rate of 200 amperes (Journ. Inst. Elec. Eng., 1904, pp. 1-36).
Subsequently Edison found some degree of falling-off in capacity, due to an enlargement of the positive pockets by pressure of gas. Most of the faults have been overcome by altering the form of the pocket and replacing the graphite by a metallic conductor in the form of flakes.
REFERENCES.—-G. Plante, Recherches sur L'electricite(Paris, 1879); Gladstone and Tribe, Chemistry of SecondaryBatteries (London, 1884); Reynier, L'Accumulateur voltaique(Paris, 1888); Heim, Die Akkumulatoren (Berlin, 1889);Hoppe, Die Akk. fur Elektricitat (Berlin, 1892); Schoop,Handbuch fur Akk. (Stuttgart, 1898): Sir E. Frankland,``Chemistry of Storage Batteries,'' Proc. Roy. Soc., 1883;Reynier, Jour. Soc. Franc. de Phys., 1884; Heim, ``U.d. Einfluss der Sauredichte auf die Kapazitat der Akk.,''Elek. Zeits., 1889; Kohlrausch and Heim, ``Ergebnisse vonVersuchen an Akk. fur Stationsbetrieb,'' Elek. Zeits.,1889; Darrieus, Bull. Soc. Intern. des Elect., 1892; F.Dolezalek, The Theory of the Lead Accumulator (London, 1906);Sir D. Salomons, Management of accumulators (London, 1906)E. J. Wade, Secondary Batteries (London, 1901); L. Jumau,Les Accumulateurs electriques (Paris, 1904). (W. HT.)
ACCURSIUS Ital. ACCORSO), FRANCISCUS (1182-1260), Italian jurist, was born at Florence about 1182. A pupil of Azo, he first practised law in his native city, and was afterwards appointed professor at Bologna, where he had great success as a teacher. He undertook the great work of arranging into one body the almost innumerable comments and remarks upon the Code, the Institutes and Digests, the confused dispersion of which among the works of different writers caused much obscurity and contradiction. This compilation, bearing the title Glossa ordinaria or magistralis, but usually known as the Great Gloss, though written in barbarous Latin, has more method than that of any preceding writer on the subject. The best edition of it is that of Denis Godefroi (1549-1621), published at Lyons in 1589, in 6 vols. folio. When Accursius was employed in this work, it is said that, hearing of a similar one proposed and begun by Odoiced, another lawyer of Bologna, he feigned indisposition, interrupted his public lectures, and shut himself up, till with the utmost expedition he had accomplished his design. Accursius was greatly extolled by the lawyers of his own and the immediately succeeding age, and he was even called the idol of jurisconsults, but those of later times formed a much lower estimate of his merits. There can be no doubt that he disentangled the sense of many laws with much skill, but it is equally undeniable that his ignorance of history and antiquities often led him into absurdities, and was the cause of many defects in his explanations and commentaries. He died at Bologna in 1260. His eldest son Franciscus (1225-1293), who also filled the chair of law at Bologna, was invited to Oxford by King Edward I., and in 1275 or 1276 read lectures on law in the university.
ACCUSATION (Lat. accusatio, accusare, to challenge to a causa, a suit or trial at law), a legal term signifying the charging of another with wrong-doing, criminal or otherwise. An accusation which is made in a court of justice during legal proceedings is privileged (see PRIVILEGE), though, should the accused have been maliciously prosecuted, he will have a right to bring an action for malicious prosecution. An accusation made outside a court of justice would, if the accusation were false, render the accuser liable to an action for defamation of character, while, if the accusation be committed to writing, the writer of it is liable to indictment, whether the accusation be made only to the party accused or to a third person, A threat or conspiracy to accuse another of a crime or of misconduct which does not amount to a crime for the purpose of extortion is in itself indictable.
ACCUSATIVE (Lat. accusativus, sc. casus, a translation of the Gr. aitiatike ptosis, the case concerned with cause and effect, from aiti'a, a cause), in grammar, a case of the noun, denoting primarily the object of verbal action or the destination of motion.
ACE (derived through the Lat. as, from the Tarentine form of the Gr. eis) the number one at dice, or the single point on a die or card; also a point in the score of racquets, lawn-tennis, tennis and other court games.
ACELDAMA (according to Acts i. 19, ``the field of blood''), the name given to the field purchased by Judas Iscariot with the money he received for the betrayal of Jesus Christ. A different version is given in Matthew xxvii. 8, where Judas is said to have cast down the money in the Temple, and the priests who had paid it to have recovered the pieces, with which they bought ``the potter's field, to bury strangers in.'' The MS. evidence is greatly in favour of a form Aceldamach. This would seem to mean ``the field of thy blood,'' which is unsuitable. Since, however, we find elsewhere one name appearing as both Sirach and Sira (ch = aleph), Aceldamach may be another form of an original Aceldama (aleph kamatz mem shvah daleth lamedh tzareh qoph patach heth), the ``field of blood.'' A. Klostermann, however, takes the ch to be part of the Aramaic root demach, ``to sleep,'; the word would then mean ``field of sleep'' or cemetery (Probleme im Aposteltexte, 1-8, 1883), an explanation which fits in well with the account in Matthew xxvii. The traditional site (now Hak el-Dum), S. of Jerusalem on the N.E. slope of the ``Hill of Evil Counsel'' (Jebel Deir Abu Tor), was used as a burial place for Christian pilgrims from the 6th century A.D. till as late, apparently, as 1697, and especially in the time of the Crusades. Near it there is a very ancient charnelhouse, partly rock-cut, partly of masonry, said to be the work of Crusaders.
ACENAPHTHENE, C12H10, a hydrocarbon isolated from the fraction of coal-tar boiling at 260 deg. -270 deg. by M. P. E. Berthelot, who, in conjunction with Bardy, afterwards synthesized it from a-ethyl naphthalene (Ann. Chem. Phys., 1873, Yol. xxix.). It forms white needles (from alcohol), melts at 95 deg. and boils at 278 deg. . Oxidation gives naphthalic acid (1.8 naphthalene dicathoxylic acid).
Acenaphthalene, C12 H8, a hydrocarbon crystallizing in yellow tables and obtained by passing the vapour of acenaphthene over heated litharge. Sodium amalgam reduces it to acenaphthone; chromic acid oxidizes it to naphthalic acid.
ACEPHALI (from a'-, privative, and kefale, head), a term applied to several sects as having no head or leader; and in particular to a strict monophysite sect that separated itself, in the end of the 5th century, from the rule of the patriarch of Alexandria (Peter Mongus), and remained ``without king or bishop'' till they were reconciled by Mark I. (799-819).1 The term is also used to denote clerici vagrantes, i.e. clergy without title or benefice, picking up a living anyhow (cf. Hinschius i. p. 64). Certain persons in England during the reign of King Henry I. were called Acephali because they had no lands by virtue of which they could acknowledge a superior lord. The name is also given to certain legendary races described by ancient naturalists and geographers as having no heads, their mouths and eyes being in their breasts, generally identified with Pliny's Blemmyae.
ACEPHALOUS, headless, whether literally or metaphorically, leaderless. The word is used literally in biology; and metaphorically in prosody or grammar for a verse or sentence with a beginning wanting. In zoology, the mollusca are divided into cephalous and acephalous (Acephala), according as they have or have not an organized part of their anatomy as the seat of the brain and special senses. The Acephala, or Lamellibranchiata (q.v.), are commonly known as bivalve shell-fish. In botany the word is used for ovaries not terminating in a stigma. Acephalocyst is the name given by R. T. H. Laennec to the hydatid, immature or larval tapeworm.
ACERENZA (anc. Aceruntia), a town of the province of Potenza, Italy, the seat of an archbishop, 15 1/2 m. N.E. of the station of Pietragalla, which is 9 m. N.W. of Potenza by rail, 2730 ft. above sea-level. Pop. (1901) 4499. Its situation is one of great strength, and it has only one entrance, on the south. It was occupied as a colony at latest by the end of the Republic, and its importance as a fortress was specially appreciated by the Goths and Lombards in the 6th and 7th centuries. It has a fine Norman cathedral, upon the gable of which is one of the best extant busts of Julian the Apostate.
ACEROSE (from Lat. acus, needle, or acer, sharp), needle-shaped, a term used in botany (since Linnaeus) as descriptive of the leaves, e.g., of pines. From Lat. aeus, chaff, comes also the distinct meaning of ``mixed with chaff.''
ACERRA, a town and episcopal see of Campania, Italy, in the province of Caserta, 9 m. N.E. from Naples by rail. Pop. (1901) 16,443. The town lies on the right bank of the Agno, which divides the province of Naples from that of Caserta, 90 ft. above the sea, in a fertile but somewhat marshy district, which in the middle ages was very malarious. The ancient name (Acerrae) was also borne by a town in Umbria and another in Gallia Transpadana (the latter now Pizzighettone on the Adda, 13 m. W.N.W. of Cremona). It became a city with Latin rights in 332 B.C. and later a municipium. It was destroyed by Hannibal in 216 B.C., but restored in 210; in 90 B.C. it served as the Roman headquarters in the Social war, and was successfully held against the insurgents. It received a colony under Augustus, but appears to have suffered much from floods of the river Clams. Under the Empire we hear no more of it, and no traces of antiquity, beyond inscriptions, remain.
ACERRA, in Roman antiquity, a small box or pot for holding incense, as distinct from the turibulum (thurible) or censer in which incense was burned. The name was also given by the Romans to a little altar placed near the dead, on which incense was offered every day till the burial. In ecclesiastical Latin the term acerra is still applied to the incense boats used in the Roman ritual.
ACETABULUM, the Latin word for a vinegar cup, an ancient Roman vessel, used as a liquid measure (equal to about half a gill); it is also a word used technically in zoology, by analogy for certain cup-shaped parts, e.g. the suckers of a mollusc, the socket of the thigh-bone, &c.; and in botany for the receptacle of Fungi.
ACETIC ACID (acidum aceticum), CH3.CO2H, one of the most important organic acids. It occurs naturally in the juice of
1 See Gibbon, ch. xlvii. (vol. v. p. 129 in Pury's ed.).
many plants, and as the esters of n-hexyl and n-octyl alcohols in the seeds of Heracleum giganteum, and in the fruit of Heracleum sphondylium, but is generally obtained, on the large scale, from the oxidation of spoiled wines, or from the destructive distillation of wood. In the former process it is obtained in the form of a dilute aqueous solution, in which also the colouring matters of the wine, salts, &c., are dissolved; and this impure acetic acid is what we ordinarily term vinegar (q.v.). Acetic acid (in the form of vinegar) was known to the ancients, who obtained it by the oxidation of alcoholic liquors. Wood-vinegar was discovered in the middle ages. Towards the close of the 18th century, A. L. Lavoisier showed that air was necessary to the formation of vinegar from alcohol. In 1830 J. B. A. Dumas converted acetic acid into trichloracetic acid, and in 1842 L. H. F. Melsens reconverted this derivative into the original acetic acid by reduction with sodium amalgam. The synthesis of trichloracetic acid from its elements was accomplished in 1843 by H. Kolbe; this taken in conjunction with Melsens's observation provided the first synthesis of acetic acid. Anhydrous acetic acid—glacial acetic acid—is a leafy crystalline mass melting at 16.7 deg. C., and possessing an exceedingly pungent smell. It boils at 118 deg. , giving a vapour of abnormal specific gravity. It dissolves in water in all proportions with at first a contraction and afterwards an increase in volume. It is detected by heating with ordinary alcohol and sulphuric acid, which gives rise to acetic ester or ethyl acetate, recognized by its fragrant odour; or by heating with arsenious oxide, which forms the pungent and poisonous cacodyl oxide. It is a monobasic acid, forming one normal and two acid potassium salts, and basic salts with iron, aluminium, lead and copper. Ferrous and ferric acetates are used as mordants; normal lead acetate is known in commerce as sugar of lead (q.v.); basic copper acetates are known as verdigris (q.v.).
Pharmacology and Therapeutics.—-Glacial acetic acid is occasionally used as a caustic for corns. The dilute acid, or vinegar, may be used to bathe the skin in fever, acting as a pleasant refrigerant. Acetic acid has no valuable properties for internal administration. Vinegar, however, which contains about 5% acetic acid, is frequently taken as a cure for obesity, but there is no warrant for this application. Its continued employment may, indeed, so injure the mucous membrane of the stomach as to interfere with digestion and so cause a morbid and dangerous reduction in weight.
The acetates constitute a valuable group of medicinal agents, the potassium salt being most frequently employed. After absorption into the blood, the acetates are oxidized to carbonates, and therefore are remote alkalies, and are administered whenever it is desired to increase the alkalinity of the blood or to reduce the acidity of the urine, without exerting the disturbing influence of alkanes upon the digestive tract. The citrates act in precisely similar fashion, and may be substituted. They are somewhat more pleasant but more expensive.
ACETO-ACETIC ESTER, C6H10O3 or CH3.CO.CH2.COOC2H5, a chemical substance discovered in 1863 by A. Geuther, who showed that the chief product of the action of sodium on ethyl acetate was a sodium compound of composition C6H9O3Na, which on treatment with acids gave a colourless, somewhat oily liquid of composition C6H10O3. E. Frankland and B. F. Duppa in 1865 examined the reaction and concluded that Geuther's sodium salt was a derivative of the ethyl ester of acetone carboxylic acid and possessed the constitution CH6CO.CHNa.COOC2H5. This view was not accepted by Geuther, who looked upon his compound C6H10O3 as being an acid. J. Wislicenus also investigated the reaction very thoroughly and accepted the Frankland-Duppa formula (Annalen, 1877, 186, p. 163; 1877, 190, p. 257).
The substance is best prepared by drying ethyl acetate over calcium chloride and treating it with sodium wire, which is best introduced in one operation; the liquid boils and is then heated on a water bath for some hours, until the sodium all dissolves. After the reaction is completed, the liquid is acidified with dilute sulphuric acid (1:5) and then shaken with salt solution, separated from the salt solution, washed, dried and fractionated. The portion boiling betbeen 175 deg. and 185 deg. C. is redistilled. The yield amounts to about 30% of that required by theory.
A. Ladenburg and J. A. Wanklyn have shown that pure ethyl acetate free from alcohol will not react with sodium to produce aceto-acetic ester. L. Claisen, whose views are now accepted, studied the reactions of sodium ethylate and showed that if sodium ethylate be used in place of sodium in the above reaction the same result is obtained. He explains the reactions
/ONaCH3.C==O + NaOC2H5 = CH3.C-OC2H5,\ OC2H5 \OC2H5
this reaction being followed by
/ONa H\CH3.C-OC2H5 + CH.COOC2H5 = 2 C2 H5OH +\OC2H5 H/ CH3.C(ONa):CH.COOC2H5;
and on acidification this last substance gives aceto-acetic ester. Aceto-acetic ester is a colourless liquid boiling at 181 deg. C.; it is slightly soluble in water, and when distilled undergoes some decomposition forming dehydracetic acid C8H8O4. It undoubtedly contains a keto-group, for it reacts with hydrocyanic acid, hydroxylamine, phenylhydrazine and ammonia; sodium bisulphite also combines with it to form a crystalline compound, hence it contains the grouping CH 3/0.CO-. J. Wislicenus found that only one hydrogen atom in the—CH2- group is directly replaceable by sodium, and that if the sodium be then replaced by an alkyl group, the second hydrogen atom in the group can be replaced in the same manner. These alkyl substitution products are important, for they lead to the synthesis of many organic compounds, on account of the fact that they can be hydrolysed in two different ways, barium hydroxide or dilute sodium hydroxide solution giving the so-called ketone hydrolysis, whilst concentrated sodium hydroxide gives the acid
Ketone hydrolysis:-CH3.CO.C(XY).CO2C2H5 -> CH3.CO.CH(XY) +C2H5OH + CO2;Acid hydrolysis:-CH3.CO.C(XY).CO2C2H5 -> CH3.CO2H + C2H5OH +CH(XY).COOH;
(where X and Y = alkyl groups).
Both reactions occur to some extent simultaneously. Acetoacetic ester is a most important synthetic reagent, having been used in the production of pyridines (q.v.), quinolines (q.v.), pyrazolones, furfurane (q.v.), pyrrols (q.v.), uric acid (q.v.), and many complex acids and ketones.
For a discussion as to the composition, and whetherit is to be regarded as possessing the ``keto', formCH3.CO.CH2.COOC2H6 or the ``enol'' form CH3.C(OH):CH.COOC2H5, see ISOMERISM, and also papers by J. Wislicenus(Ann., 1877, 186, p. 163; 1877, 190, p. 257), A. Michael(Journ. Prak. Chem., 1887, [2] 37, p. 473), L. Knorr(Ann., 1886, 238, p. 147), W. H. Perkin, senr. (Journ. ofChem. Soc., 1892, 61, p. 800) and J. U. Nef (Ann., 1891,266, p. 70; 1892, 270, pp. 289, 333; 1893, 276, p. 212).
ACETONE, or DIMETHYL KETONE, CH3.CO.CH3, in chemistry, the simplest representative of the aliphatic ketones. It is present in very small quantity in normal urine, in the blood, and in larger quantities in diabetic patients. It is found among the products formed in the destructive distillation of wood, sugar, cellulose, &c., and for this reason it is always present in crude wood spirit, from which the greater portion of it may be re-covered by fractional distillation. On the large scale it is prepared by the dry distillation of calcium acetate (CH3CO2)2Ca = CaCO3 + CH3COCH3. E. R. Squibb (Journ. Amer. Chem. Soc., 1895, 17, p. 187) manufactures it by passing the vapour of acetic acid through a rotating iron cylinder containing a mixture of pumice and precipitated barium carbonate, and kept at a temperature of from 500 deg. C. to 600 deg. C. The mixed vapours of acetone, acetic acid and water are then led through a condensing apparatus so that the acetic acid and water are first condensed, and then the acetone is condensed in a second vessel. The barium carbonate used in the process acts as a contact substance, since the temperature at which the operation is carried out is always above the decomposition point of barium acetate. Crude acetone may be purified by converting it into the crystalline sodium bisulphite compound, which is separated by filtration and then distilled with sodium
CH3\ / OH CH3\2 C + Na2CO3 = 2 CO + 2 Na2SO3 +CH3/ \ SO3Na CH3/ CO2 + H2O
It is then dehydrated and redistilled.
Acetone is largely used in the manufacture of cordite (q.v.) For this purpose the crude distillate is redistilled over sulphuric acid and then fractionated.
Acetone is a colourless mobile liquid of pleasant smell, boiling at 56.53 deg. C., and has a specific gravity 0.819 (0 deg. /4 deg. C.). It is readily soluble in water, alcohol, ether, &c. In addition to its application in the cordite industry it is used in the manufacture of chloroform (q.v.) and sulphonal, and as a solvent. It forms a hydrazone with phenyl hydrazine, and an oxime with hydroxylamine. Reduction by sodium amalgam converts it into isopropyl alcohol; oxidation by chromic acid gives carbon dioxide and acetic acid. With ammonia it reacts to form di- and triacetoneamines. It also unites directly with hydrocyanic acid to form the nitrile of a-oxyisobutyric acid.
By the action of various reagents such as lime, caustic potash, hydrochloric acid, &c., acetone is converted into condensation products, mesityl oxide C6H10O, phorone C9H14O, &c., being formed. On distillation with sulphuric acid, it is converted into mesitylene C9H12 (symmetrical trimethyl benzene). Acetone has also been used in the artificial production of indigo. In the presence of iodine and an alkali it gives iodoform. Acetone has been employed medicinally in cases of dyspnoea. With potassium iodide, glycerin and water, it forms the preparation spirone, which has been used as a spray inhalation in paroxysmal sneezing and asthma.
ACETOPHENONE, or PHENYL-METHYL KETONE, C8H8O or C6H5CO.CH3, in chemistry, the simplest representative of the class of mixed aliphatic-aromatic ketones. It can be prepared by distilling a mixture of dry calcium benzoate and acetate, Ca(O2CC6H5)2 + (CH3CO2)2Ca = 2CaCO3 + 2 C6H5CO.CH3, or by condensing benzene with acetyl chloride in the presence of anhydrous aluminium chloride (C. Friedel and J. M. Crafts), C6H6+CH3COCl == HCl + C6H5COCH3. It crystallizes in colourless plates melting at 20 deg. C. and bolling at 202 deg. C.; it is insoluble in water, but readily dissolves in the ordinary organic solvents. It is reduced by nascent hydrogen to the secondary alcohol C6H5.CH.OH.CH3 phenyl-methyl-carbinol, and on oxidation forms benzoic acid. On the addition of phenylhydrazine it gives a phenylhydrazone, and with hydroxylamine furnishes an
melting at 59 deg. C. This oxime undergoes a peculiar rearrangement when it is dissolved in ether and phosphorus pentachloride is added to the ethereal solution, the excess of ether distilled off and water added to the residue being converted into the isomeric substance acetanilide, C6H5NHCOCH3, a behaviour shown by many ketoximes and known as the Beckmann change (see Berichte, 1886, 19, p. 988). With sodium ethylate in ethyl acetate solution it forms the sodium derivative of benzoyl acetone, from which benzoyl acetone, C6H5.CO.CH2.CO.CH3, can be obtained by acidification with acetic acid. When heated with the halogens, acetophenone is substituted in the aliphatic portion of the nucleus; thus bromine gives phenacyl bromide, C6H6CO.CH2Br. Numerous derivatives of acetophenone have been prepared, one of the most important being orthoaminoacetophenone, NH2.C6H4.CO.CH3, which is obtained by boiling orthoaminophenylpropiolic acid with water. It is a thick yellowish oil bolling between 242 deg. C. and 250 deg. C. It condenses with acetone in the presence of caustic soda to a quinoline. Acetonyl-aeeto phenone, C6H5 . CO . CH2 . CH2. CO . CH3, is produced by condensing phenacyl bromide with sodium acetoacetate with subsequent elimination of carbon dioxide, and on dehydration gives aa-phenyl-methyl-furfurane. Oxazoles (q.v.) are produced on condensing phenacyl bromide with acid-amides (M. Lewy, Berichte, 1887, 20, p. 2578). K. L. Paal has also obtained pyrrol derivatives by condensing acetophenone-aceto- acetic-ester with substances of the type NH2R.
ACETYLENE, klumene or ethine, a gaseous compound of carbon and hydrogen, represented by the formula C2H2.
Physical properties.
It is a colourless gas, having a density of 0.92. When prepared by the action of water upon calcium carbide, it has a very strong and penetrating odour, but when it is thoroughly purified from sulphuretted and phosphuretted hydrogen, which are invariably present with it in minute traces, this extremely pungent odour disappears, and the pure gas has a not unpleasant ethereal smell. It can be condensed into the liquid state by cold or by pressure, and experiments by G. Ansdell show that if the gas be subjected to a pressure of 21.53 atmospheres at a temperature of 0 deg. C., it is converted into the liquid state, the pressure needed increasing with the rise of temperature, and decreasing with the lowering of the temperature, until at—82 deg. C. it becomes liquid under ordinary atmospheric pressure. The critical point of the gas is 37 C., at which temperature a pressure of 68 atmospheres is required for liquefaction. The properties of liquid and solid acetylene have been investigated by D. Mcintosh (Jour Chem. Soc., Abs., 1907, i. 458). A great future was expected from its use in the liquid state, since a cylinder fitted with the necessary reducing valves would supply the gas to light a house for a considerable period, the liquid occupying about 1/400 the volume of the gas, but in the United States and on the continent of Europe, where liquefied acetylene was made on the large scale, several fatal accidents occurred owing to its explosion under not easily explained conditions. As a result of these accidents M. P. E. Berthelot and L. J. G. Vieille made a series of valuable researches upon the explosion of acetylene under various conditions. They found that if liquid acetylene in a steel bottle be heated at one point by a platinum wire raised to a red heat, the whole mass decomposes and gives rise to such tremendous pressures that no cylinder would be able to withstand them. These pressures varied from 71,000 to 100,000 lb. per square inch. They, moreover, tried the effect of shock upon the liquid, and found that the repeated dropping of the cylinder from a height of nearly 20 feet upon a large steel anvil gave no explosion, but that when the cylinder was crushed under a heavy blow the impact was followed, after a short interval of time, by an explosion which was manifestly due to the fracture of the cylinder and the ignition of the escaping gas, mixed with air, from sparks caused by the breaking of the metal. A similar explosion will frequently follow the breaking in the same way of a cylinder charged with hydrogen at a high pressure. Continuing these experiments, they found that in acetylene gas under ordinary pressures the decomposition brought about in one portion of the gas, either by heat or the firing in it of a small detonator, did not spread far beyond the point at which the decomposition started, while if the acetylene was compressed to a pressure of more than 30 lb. on the square inch, the decomposition travelled throughout the mass and became in reality detonation. These results showed clearly that liquefied acetylene was far too dangerous for general introduction for domestic purposes, since, although the occasions would be rare in which the requisite temperature to bring about detonation would be reached, still, if this point were attained, the results would be of a most disastrous character. The fact that several accidents had already happened accentuated the risk, and in Great Britain the storage and use of liquefied acetylene are prohibited.