FIGS 4, 4B, 4CFigs. 4, 4B and 4C
The Oerlikon lamp, which is designed to work with constant potential, is shown partly in section in Fig. 8. There is only one solenoid, A, through which all the current passes, and whose action is to strike the arc and maintain the current constant. The soft iron core, C, is suspended from the inside of the tube, T, in which it has an up and down movement checked by an air piston in the tube. An end elevation of the brake wheels and solenoid is given in Fig. 9, where it will be seen that the spindle carrying these wheels also carries between them a pinion engaging with the rack rod, R. The top carbon attached to the rack rod falls by its own weight, and is therefore in contact with the lower carbon before the lamp is switched in circuit. When this is done the core is instantly magnetized, and attracted to the soft iron brake wheels, which it holds firmly. The air cushion in the tube prevents the core being drawn up until it has fairly gripped the sides of the wheels. The subsequent raising of the core therefore turns the wheels, raises the rack rod, and strikes the arc. The feed is operated by the weakening of the magnetic field of the coil, which causes the core to lose its grip of the wheels, and allows the top carbon to descend. The catch, L, Fig. 8, has a lateral play, and serves to engage in the teeth of the rack rod, so as to prevent its falling when being trimmed. Each carbon when in position is held against two rectangular guide bars by the pressure of a wire spring—see figure. In this way the carbon is pressed against two parallel knife edges, and is therefore always in true alignment. The action of the lamp is very simple, the working parts are few and solidly constructed, and the regulation, as exhibited by the lamps running in the galleries, is exceptionally steady.
The transmission of power plant consists of two 250 horse power dynamos—C.E.L. Brown's patent—the generator being driven by a vertical compound condensing engine of the same power, running at 180 revolutions. The dynamo generator is a four-pole 600 volt direct current machine, series wound, and may be distinguished in the engraving next to the switch board; while the motor receiver connected to it, and erected in another portion of the Swiss section, is of exactly the same size and type. The field, which is hexagonal in shape, is cast in two pieces, bolted together horizontally, the cross-sectional area of iron being 170 square inches. The armature is cylindrical, and built up of flat rings stamped out of soft sheet iron, eight notches in the same being provided to fit over the arms of the spider keyed to the shaft. The spider is in halves, which are bolted together longitudinally after the rings are in position. It is Gramme wound, and measures over the winding 7 in. radial depth, 37 in. outside diameter, and 22 in. in length. The current is collected by four brushes. The fitting and mechanical build of the dynamos leaves nothing to be desired. All the working parts of the dynamos and engines are turned up to gauge and template, so as to be interchangeable. As an instance of this, the armature of the generator was built in the works, while the field magnets were being erected in the exhibition, and, on arrival, fitted in position perfectly, and ran at once without trouble.
The energy taken off on the motor shaft is close on 200 horse power, but varies according to the machines at work; the speed of the motor does not, however, vary more than 3 per cent., and the brushes need no adjustment. About 6 ft. of shafting is coupled on in line with the motor shaft, and an extra plummer block fixed at the end. This shafting carries at its extremity an additional 2 ft. pulley, the power being delivered by belting from these pulleys to two large pulleys on the main shaft.
The machines run by this transmission consist of the looms of Rieter & Co., of Winterthur; the large flour mill and lift of A. Millot & Co.; the flour milling machinery of Frederick Wegmann & Co., of Zurich; the brick and tile making machines of the Rorschach foundries; and the looms of Messrs. Houget & Teston, of Verviers, in the Belgian section. A 15 horse power two-pole Oerlikon dynamo is also run by a belt from the main shaft, and generates power to drive a motor of similar type in the Swiss section of the upper gallery. This runs a length of countershafting supplying power to three silk-weaving machines constructed by Benninger Frères; six weaving machines from the Ruti works, near Zurich; and one knitting machine exhibited by Edward Dubied & Co., of Couvet.
The dynamo and motor are connected to the main cable by switches of the type shown in Fig. 5. These are specially designed to destroy the extra current on breaking circuit by the formation of an arc which gradually increases the resistance till the break occurs, rendering it less sudden. One wire passes through the handle and makes contact with the springs, and the other is attached to the clamp in which the carbon rod is held. The current is made to enter at the carbon rod, so that the arcs formed cause consumption of the carbon. A magnetic cut-out—Fig. 6—is also provided to each machine; this consists of an electro-magnet, through which the main current passes, provided with side pole pieces. A flat soft iron plate armature is hinged so as to come up against the pole pieces when attracted. When the current is not sufficiently strong to cause the plate to be attracted, a hole in the center of the latter engages over a small projection in the top of a weighted arm hinged in the center of the board, and keeps it upright. If now the current exceeds the limits of safety to the machine, due to a too heavy load being thrown on, the armature is attracted and releases the vertical arm, which falls over and enters with considerable force between the two spring contacts below. These contacts are connected to the field terminals, which are, therefore, short-circuited, and prevent the dynamo generating any current. A retractile spring can be adjusted to cause cut-off at any required current. These details are indicated in our illustrations mounted on their respective switch boards.
Since the erection of plant by these works at Solothurn for transmitting 50 horse power five miles distant, which attracted so much interest some time ago, several important works have been carried out. Among these we may mention a 280 horse power transmission at 1½ kilom. distance to a cotton mill at Derendingen in Switzerland, a 250 horse power transmission at ½ kilom. distance, carried out for Gaetano Rossi at Piovene in Italy, and a 300 horse transmission at 6 kilom. distance installed for Giovanni Rossi, in which the power is given off at two different stations.—The Engineer.
Although telephonic novelties are not numerous at the Universal Exposition, telephony—that quite young branch of electric science—is daily the object of curiousand interesting experiments which we must make known to our readers, a large number of whom were not yet born to scientific life when the experiments were made for the first time at Paris in 1881; and it is proper to congratulate the Société Générale des Téléphones on having repeated them in 1889 to the great satisfaction of the rising generation.
We allude to the Ader system of telephonic transmissions of sounds in such a way that they can be heard by an audience.
The essential parts of this mode of transmission consist of two distinct systems—transmitters and receivers.
Fig. 1.—THE ADER FLOURISH OF TRUMPETSFig. 1.—THE ADER FLOURISH OF TRUMPETS
Fig. 2.—DETAILS OF THE TRANSMITTER.Fig. 2.—DETAILS OF THE TRANSMITTER.
The transmitters are four in number, and are actuated by the same number of musicians, each humming into them his part of the quartet (Fig. 1). This transmitter, represented apart in elevation and section in Fig. 2, is identical with the one used in the curious experiment with the singing condenser. At A is a mouthpiece before which the musician hums his part as upon a reed pipe. He causes the plate, B, to vibrate in unison with the sound that he emits, and this produces periodical interruptions of varying rapidity between the disk, B, and the point, C. The button, D, serves to regulate the distance in such a way that the breakings of the circuit shall be very complete and produce sounds in the receivers as pure as allowed by this special mode of transmission, in which all the harmonics are systematically suppressed in order to re-enforce the fundamental.
Fig. 3.—THE ADER FLOURISH OF TRUMPETSFig. 3.—THE ADER FLOURISH OF TRUMPETS
This transmitter interrupter is interposed in the circuit of a battery of accumulators, with the five receivers that it actuates, in such a way that the four transmitters and five receivers form in reality four groups of distinct autonomous transmission, the accordance of which is absolutely dependent upon that of the artists who make them vibrate.
Fig. 4.—DETAILS OF THE RECEIVER.Fig. 4.—DETAILS OF THE RECEIVER.
The five receivers are arranged over the front door of the telephone pavilion, near the Eiffel tower (Fig. 3). Each consists of a horseshoe magnet provided, between its branches, with two small iron cores having a space of a few millimeters between them (Fig. 4). Each of these soft iron cores carries a copper wire bobbin, N, the number of spirals of which is properly calculated for the effect to be produced. Opposite the vacant space left by the two cores, there is a small piece,t, of rectangular form, and also of soft iron, fixed to a vibrating strip of firwood, L, of about 4 inches section. The periodical breaking of the circuit produced by the transmitter causes a variation in the magnetization of the iron cores of the five receivers and makes the firwood strips vibrate energetically. These vibrations are received and poured forth as it were in front of the telephone pavilion, by large brass trumpets arranged in front of each receiver, as shown in Fig. 3.
It would be difficult for us to pass any judgment whatever upon the musical and artistic value of these transmissions of trumpet music to a distance; we prefer to confess our incompetency in the matter. But it is none the less certain that these experiments are having the same success that they had at their inception in 1881 at the Universal Exposition of Electricity, and they allow us to foresee that there is a time coming in which it will be possible to transmit speech to a distance with the same intensity that the present trumpet flourishes have. Although all the tentatives hitherto made in this direction have not given very brilliant results, we must not despair of attaining the end some day or other. Less than fifteen years ago the telephone did not exist; now it covers the world with its lines.—La Nature.
During the last ten years there has been an enormous increase in the production of these preparations, and the time will come when their application in dyeing and calico printing will become so general as to completely supersede the employment of the raw materials. The manufacture of these extracts, to be thoroughly successful, requires to be so conducted as to secure the perfect exhaustion of the dyewoods without the slightest destruction or deterioration of the coloring matters contained in them; and though nothing like perfection has been reached in the attainment of these objects, it is certain that the processes of extraction and evaporation now employed by the best makers are a very great improvement on the older methods. Indeed, there is no difficulty nowadays in procuring dyewood extracts of high excellence if the consumer is willing to pay a price for them corresponding to their quality, and knows how to avail himself of the aid of chemical skill to control his purchases. Unfortunately, however, there is so much hankering after cheap articles, and so little care is taken to ascertain their real quality, that every scope is afforded to the malpractices of the adulterer. There are many dye and print works in which large quantities of these extracts are used without being subjected to trustworthy tests. Moreover, much of the testing is done by fallacious methods and often by biased hands. So fallacious, indeed, are some of these tests, that grossly adulterated extracts are often declared superior to the purer ones, the cause of this being the application of an insufficient proportion of mordant in the dyeing or printing trials, and the consequent waste of the excess of coloring matter in the case of the purer preparation.
Professional analytical chemists have hitherto given but little attention to these preparations, and the employment of experienced chemists in works is as yet far from general. The testing of dyewood extracts in such a manner as to throw full light on their purity, the quality of raw material from which they are prepared, their exact commercial value their suitability for special purposes, and the proportion and nature of any adulterants they may contain, is of course a difficult and tedious task, and must be left to the expert who is in possession of authentic specimens prepared by himself of all the different extracts made from every variety and quality of raw materials, and who combines a thorough knowledge of experimental dyeing and printing with a large experience in the chemical investigation of these preparations. But when the object of the testing is merely careful comparison of the sample in question with an original sample or previous deliveries, the case is much simplified, and comes within the scope of the general chemist or the laboratory attached to works. A few years ago I recommended carefully conducted dyeing trials on woolen cloth mordanted with bichromate of potash as the best and simplest mode adapted to such cases, and my subsequent experience enables me to confirm that observation to the fullest extent. Most of these extracts contain the coloring matter in two states, the developed and the undeveloped, and an oxidizing mordant such as bichromate of potash causes the latter as well as the former to enter completely into combination with a metallic base; whereas many of the other mordants, such as alumina or tin compounds, merely take up the developed portion of the coloring matter together with such small and variable proportions of the undeveloped as might undergo oxidation during the process of dyeing. I would therefore suggest dyeing trials with alumina, tin, iron, etc., only as subsidiary tests indicating the suitability of an extract for certain special purposes, while recommending the trial with bichromate of potash as the one giving the best information respecting the actual strength of the extract in relation to the raw material from which it was obtained, and as giving a fair idea of the money value of the sample. Cotton dyeing does not, as a general rule, afford a good means of assaying extracts, as it is generally done under conditions which do not admit of complete exhaustion of the dye bath, but it might often with advantage be resorted to as an additional trial throwing further light on the degree of oxidation or development of the coloring matter. Printing trials are apt to give fallacious results unless the proportion of mordant is carefully adjusted to the amount of coloring matter present, and several trials with different proportions would be necessary to prevent erroneous conclusions. For the trials with bichromate of potash on wool I would recommend pieces of cloth weighing about 150 grains, and the most suitable proportion of bichromate of potash is 3 per cent. of the weight of the cloth. The requisite number of pieces (equal to the number of samples to be tested) should be thoroughly scoured and then heated in the bichromate solution at or near the boiling point for not less than 1½ hours, after which they should be well washed and then dyed separately in the solutions of equal weights of the extracts at the same temperature and for the same length of time; 15 grains of extract is a suitable quantity for a first trial under these conditions. These trials can then be repeated with different relative proportions of extract in order to ascertain what weight of a sample would give the same depth of color as 15 grains of the standard example. Many precautions are required both in the mordanting and dyeing processes in order to obtain trustworthy results; and though the trials with bichromate of potash give the most reliable information of any single test, they should be supplemented by the subsidiary tests already alluded to, and also by a chemical examination, in order to obtain a knowledge, not merely of the wood strength, but also of the general nature of the extract. An adulteration with molasses or glucose can be best determined by fermentation in comparison with a pure sample. Mineral adulterants may, of course, be detected by an estimation and analysis of the ash, after making due allowances for variations due to differences in different kinds of the same dyewoods. The estimation of the individual coloring matters in these extracts by means of a chemical analysis is under all circumstances a task requiring much experience, especially as the coloring principles are associated in different qualities of each class of dyewood with different proportions of other constituents which often give much trouble to the unpracticed experimenter. Extracts made from logwood roots are now largely manufactured and often substituted or mixed with the extracts of real logwood, and have in some instances been palmed of as logwood extracts of high quality. The correct determination of such admixtures, like the fixing of anything like the exact commercial value of dyewood extracts, requires nothing less than a complete chemical investigation coupled with numerous dyeing trials in comparison with standard preparations, and should be left to an expert.
The presence in dyewood extracts of coloring matters in various stages of development has hitherto militated against their use in place of the raw materials by many dyers and printers who are still employing inherited and antiquated processes in which the whole of the coloring matter is not rendered available. It is often asserted by these that even the best of extracts fail to give anything like the results attained by the use of well-prepared woods, and that, indeed, their application proves a complete failure. Such failure, however, is simply due to the want of chemical knowledge on the part of the dyers, for there is no real difficulty in making any good and pure extract serve all the purposes for which the woods were used. It is to be hoped that in this branch of industry, as well as in many others, the employment of chemists will become more general than at present, and not be restricted, as is often the case, to young men without experience and without the trained intellect so essential to success in chemical investigations. High class chemical skill is of course available to the manufacturer, but the man of science who brings matured knowledge and valuable brain work into the business required social as well as pecuniary recognition, and the sooner and more fuller this fact is appreciated the better it will be for the maintenance and progress of our industries.
With regard to the astringent extracts, such as sumac, myrabolam, divi, valonia, quebracho, oak, etc., it is the aim of the manufacturer, whenever such extracts are intended for the purposes of dyeing and printing, to obtain the tannin in a form in which it isbest calculated to fix itself upon the fiber. The case is somewhat different when the same extracts are required for tanning. For this purpose it is necessary that the extract shall have considerable permeating power, and that the tannin contained in it shall readily yield leather of the desired texture, color, and permanency. Extracts specially suited for this purpose are by no means always the most suitable for the dyer, andvice versa.
A brief description of the processes by which the astringent extracts may be tested with particular reference to their fitness for definite purposes concluded the paper.
With regard to the question as to whether experimental dyeing with bichromate of potash should be employed as a test even in works where all the dyeing was done with other mordants, he was decidedly of opinion that it should always be resorted to as one of the tests, inasmuch as it was the only simple and expeditious method giving a fair idea of the actual wood strength and money value of the extract. The test should, in such cases, be supplemented by dyeing trials with the mordants used at the works, and, if necessary, also by a chemical analysis. Printing trials were not necessarily bad tests, since oxidizing was usually added in these where it was necessary, and any undeveloped coloring matter would thus be oxidized during the steaming process: but, as he had stated before, it was essentially necessary in such cases to have a fair idea of the amount of actual coloring matter in the extract and to adjust the proportion of mordant accordingly. Such trials should therefore be preceded by carefully conducted dyeing trials with bichromate of potash. Mr. Thomson had raised the question whether it would not be well for the manufacturer to prepare these extracts in such a manner that they would contain all the coloring matter in one condition only, in order to insure greater uniformity in their quality and mode of application. This would, no doubt, be a desirable step to take if the owners of dye and print works were more in the habit of availing themselves of the service of competent chemists experienced in this branch, for then they would be able to make any extract do its full work irrespective of the state of development of the coloring matter. Such, however, was not the case, and it was a very common thing for the consumer of dyewood extracts to require the manufacturer to prepare them specially for him so as to suit his own dyeing recipes, or in other words to give exactly the same shades, weight for weight, by his own method of dyeing as the article he was in the habit of using. The manufacturer was thus often compelled to make many different qualities of the same extract to suit different customers. For the same reason adulterated articles were often preferred to the pure ones. There was, perhaps, no branch of industry in which chemical skill of a high order could be applied with greater advantage than in dyeing, and nowhere was this fact less recognized. Some of the processes of dyeing were exceedingly wasteful and stood in much need of improvement. He (Mr. Siebold) knew a large works in which a ton of logwood extract was used daily for black dyeing only, and he might safely assert that of this enormous quantity only a very small proportion would be fixed on the fiber, while by far the greater proportion was utterly wasted. Such a waste could only be prevented by a searching investigation of its causes by trained skill. Mr. Thomson had further alluded to the color obtained with logwood or logwood extract and wool mordanted with bichromate of potash, and seemed to be under the impression that the color thus obtained was not black, but blue. This was undoubtedly the case in dyeing trials performed as tests, as these were conducted purposely with a very small proportion of coloring matter in order to admit of a better comparison of the resulting depth of shades. But with larger proportions of logwood the color obtained was a fine bluish-black, and with the addition of a small proportion of fustic or quercitron bark to the logwood a jet black was readily produced. With regard to Mr. Watson Smith's observation as to fractional dyeing, he (Mr. Siebold) did not regard this method as a suitable trial for ascertaining the strength of an extract, but he admitted it was occasionally very valuable for detecting an admixture of extracts of other dyewoods, such as quercitron bark extract in logwood extract. It was also a good method of ascertaining the speed of dyeing and hence the relative proportion of fully developed coloring matter of an extract.—Jour. Soc. Chem. Industry.
What I want to show is the manner in which the process has been tested. My employer, Mr. Bierstadt, has given me permission to show you some samples, and also his chart containing the spectrum colors: violet, indigo blue, green, yellow, orange, red, and black. This chart has been photographed in the orthochromatic and also in the ordinary way.
There are many ways of producing an orthochromatic effect; one is the use of a glass tank placed behind or in front of the lens, in which a coloring matter from either a vegetable or mineral product is placed; this tank or cell is, however, only for use in the studio, as for outdoor photography we have a colored glass screen, so as not to be bothered with carrying colored solution.
The tank is constructed as follows: Procure two pieces of best white plate glass, about 6 inches square; between these place a piece of rubber of the same size square, and about 3/8 of an inch thick. In the center of this rubber cut out a circle about 4 inches diameter, and from one of the corners to the center of the circle cut out a narrow strip ¼ inch wide; this serves as the mouth of the tank. The two pieces of glass and the rubber are cemented together with rubber cement; then, to hold it firmly together, two brass flanges are used as a clamp, with four screws at an equal distance apart; a thin sheet of rubber is on the glass side of the flanges to prevent direct contact with the glass, the center remaining clear for the rays of light to pass through solution and glass.
One of the best orthochromatic effects made through this tank is with a three-grains-to-the-ounce solution of bichromatic of ammonia or bichromate of potassium. In this method there is no preparation used on the plate. A common rapid dry plate is exposed through this solution; the exposure, however, is about twenty times longer than it would be if you removed the tank with the yellow solution, or, in other words, if a dry-plate is exposed one minute without the yellow solution it would have to be exposed twenty minutes through a three-grain solution of bichromate of potassium or ammonia. It produces wonderful results on an oil painting or any highly colored object.
Another method, and the one best adapted for landscapes, is to bathe the plate in erythrosine and then expose it through a yellow glass screen.
As an illustration, suppose we have before us a beautiful landscape. In the foreground beautiful foliage, in the center a lake, in the distance hills, with a bluish haze appearing pleasing to the eye, also a nice sky with light clouds. Now make a plain negative, and see what has become of your clouds, hills, and the distance—not visible! Some photographers have been led to think that by underexposing they retain the distance, but they sacrifice the foreground; besides, it does not produce an orthochromatic effect.
But it is a good idea to expose longer on the foreground than you do on the distance. This can be done by raising the cap of the lens skyward and gradually shut off, giving the foreground more exposure.
Plates are prepared for orthochromatic work as follows: Take any ordinary rapid dry plate, place it in a bath containing
Distilled water200 c.c.Strong liquid ammonia2 c.c.
Rock it for two minutes, work as dark as you possibly can. Now take it out, and place it in the second bath for one and one-fourth minutes and keep it rocking. Have on hand for use a stock solution of
Distilled water1,000 parts.Erythrosine "Y" brand1 part.
Prepare second bath as follows:
Erythrosine stock solution25 c.c.Distilled water175 c.c.Strong water ammonia4 c.c.
After removing the plate, dip it again face down to rinse off any particles of scum, etc., that may get in the bath accidentally. This bath may be used for one dozen 8 by 10, when it should be thrown away and fresh bath used.
After the plates come out of the last bath, they should be stood on clean blotting paper to absorb the excess of solution. I would also advise to use clean fingers. Pyro. or hypo. on the fingers is a drawback to success.
After plates have been drained, place them in a cleaned rack in an absolutely light-tight closet, with air holes so constructed as to admit air but no light; the plates will dry in from eight to twelve hours. They are best prepared in the evening, and, if the closet is good, will be dry in the morning.
After the plates are dry they may be packed face to face with nothing between them, in a double-cover paper box, and put in a dark closet free from sulphureted hydrogen gas, until ready for use. I have kept plates for three months in this way, and they were in good condition. Great care should be used in developing these plates, as they are sensitive to the red; get used to developing in a dark part of the dark room; occasionally you may look at the process of development in a little stronger light.
The exposure through the yellow screen with an erythrosine plate is about the same as if you had no orthochromatic plate—a plain plate instead—provided you are not using too dark a yellow on your screen. This can only be determined by experience. I will give to a common plate about four seconds, an orthochromatic plate under the same conditions five seconds.
The yellow glass screen is prepared as follows: Take a piece of best plate glass—common cannot be used—clean it nicely; take another large plate glass, or anything that is level and true, level it with a small spirit-level. Now take the cleaned piece of glass and coat it with
AURENTIA COLLODION.Ether5oz.Alcohol5oz.Cotton60grs.
The aurentia to be added to suit your judgment; it takes a very small quantity to make an intense yellowish-red collodion. Pour it on the center of the glass, flow it to the edges, and before it sets place it on the level glass and allow it to set; when set put it in a rack to dry.
Should it dry in ridges, the collodion may be too thick, and it must be thinned down with equal parts of alcohol and ether. A single piece of plate glass, about one-eighth inch thick, coated with aurentia collodion, is all that is required with an erythrosine plate. Or, after a piece has been successfully coated, another piece of the same plate glass, and the same size, may be cemented together with balsam, having the coated aurentia side between the two glasses; the edges may then be bound with paper.
In using different colored solutions, collodion, etc., I have found that one will change the focus and the other not. With some screens you must focus with them in their positions; take away the screen, and the picture appears out of focus. I cannot fully explain why it is, and for this reason will not make the attempt; experience alone can teach it.
Another thing that has been tried lately is to do away with the yellow screen by substituting a yellow coating direct on the plate. No doubt the focus on an object that requires absolute sharpness is somewhat affected by the use of a glass. We have been successful, on a small scale, to coat the plate with the following yellow solution:
Place in a tray enough of a saturated solution of tropæolin in wood alcohol to cover the plate; allow it to remain ten seconds. It is necessary that the plate should be bathed previously in erythrosine and dried. Before applying the tropæolin, which, being in alcohol, dries in a few minutes, have some blotting paper on hand, as the solution gathers in a pool and leaves bad marks on the end of the plate.
The plate can be developed in the usual way. Try it and see the results.—Reported in the Beacon.
[1]
Read before the Photographic Association of Brooklyn.
Read before the Photographic Association of Brooklyn.
Platinotype, which may be considered to be the most artistic of photographic printing processes, may be separated into its three modifications—the hot bath and cold bath, in which a faintly visible image is developed, and the Pizzighelli printing-out paper. The hot bath process, again, may be divided into the black and white and sepia papers. I intend to give you a rough outline of the preparation of the paper and working of these modifications, concluding by demonstrating the hot bath method, and handing around prints by it.
Platinotype may almost be styled an iron printing process, for, while no trace of iron or its salts is found in the finished print, certain salts of iron are mixed with the platinum salt, which is platinum combined with two atoms of chlorine (PtCl2), as a means for readily reducing it; this, however, cannot be effected without the presence of neutral oxalate of potash, hence the use of the oxalate bath. There is no platinum in the paper for the cold bath process, it being coated with ferric oxalate mixed with a very small quantity of chloride of mercury—somewhere about one grain to an ounce of ferric oxalate solution. When dry it is ready for exposure, which is about three times less than with silver printing.
It is absolutely necessary to store all papers for platinum printing in an air-tight tin containing chloride of calcium, which must be dried by heating from time to time. For the cold bath, however, it is important to have moisture present during printing, or it may be after printing and before development. If the paper is left in a dampish room for fifteen minutes, it should be sufficient. Prints made by exposing damp paper, or damping dry paper just before development, must be developed within one hour if the maximum of vigor is desired; by delaying the development some hours, the prints in the meantime being stored in a drawer so that they may retain their moisture, an increase of half tone and warmth of color will be obtained. If it should be necessary to delay development for a day or two, the prints must be dried before a fire soon after being removed from the frames, and then stored in a calcium tube until wanted for development.
While printing, the lemon color of the paper receives a grayish colored image, which, although faint, can, with practice, be judged as easily as silver printing.
The developer consists of oxalate of potash and potassic chloro-platinite—about thirty grains of the platinum salt to half an ounce of oxalate forming about six ounces of solution; a great many variations, however, may be made in the proportions of platinum salt and oxalate, and different effects secured. Development is effected by sliding the print face downward on to the developer, which must be rocked after the development of each print to avoid scum marks. To clear the prints they are washed in three or four baths of a weak solution of hydrochloric acid after leaving the developer, to remove all traces of the iron salts, and finally washed for a quarter of an hour in three changes of water; they are then finished, and may be dried between clean blotting paper.
Pizzighelli's process differs from the above in being one that prints fully out in the frame without development; the paper contains the platinum and iron salts as well as the developer, and so prints and develops at the same time. Although excellent prints can be produced with it, for general work the results of the paper, as at present made, will not compare with the hot and cold bath processes. It is, however, excellent for printing from very dense negatives, and occasional negatives that seem extremely suitable for it. The paper should be breathed on before printing, as if it is quite dry the printing will be very slow and irregular. The best conditions for the preparation of the paper have scarcely been decided upon yet, and it is not quite fair to judge the process. The prints are cleared in the acid baths and washed for about a quarter of an hour.
The sepia and black hot bath processes are much alike in the general treatment. There are, however, some special precautions to be observed with the sepia paper, the chief being to protect it from any but the faintest rays of light; the prints, unlike the black ones, may be affected by light when in the acid bath. A special solution must be added to the developer to keep the lights pure. Over-exposure cannot be corrected by using a cooler bath, as is the case with the black prints, and the paper does not remain good so long.
The paper for the black prints by the hot bath process is washed with a mixture of potassic platinous chloride and ferric oxalate, the proportion being about sixty grains of the platinum salt to one ounce of the iron solution. It will not keep good longer than twenty minutes or so, and must be applied to the paper directly after mixing. The ferric oxalate in the paper is reduced by the action of light to ferrous oxalate, which forms the faint visible image; this, when the paper is floated on the oxalate of potash bath, is capable of reducing the platinum salt in contact with it into metallic platinum; but the ferric salt, which remains unaltered, has no action on the platinum salt, leaving these parts, which represent the high lights of the print, untouched. The ferric oxalate is removed by the acid baths which follow the development. A good temperature for development is 150° Fahr., and when using this so much detail should not be apparent as when printing for the cold bath process, in which all the detail desired should be very faintly visible. There are, however, many methods of exposing the paper and developing it, and no fixed rule can be made, but the development must in every case be suited to the exposure or the result will be a failure. For instance, the paper may be printed until all detail is visible, but a very much cooler development must be used, say 80° or 90°; on the other hand, a slightly short exposure may be given, and a temperature of 180° to 200° used. 150° should be taken as the normal temperature, and kept to until some experience has been gained, as employing all temperatures will lead to confusion, and nothing will be learned. Some negatives require a special treatment, and both printing and development must be altered, while for a very dense negative the paper may be left out in a dampish room for some time. It will then print with less contrast and more half tone. A thin negative is better printed by the cold bath process, but negativesshould be good and brilliant for platinotype printing. Any one taking up platinotype and getting only weak prints would do well to look to his negatives instead of blaming the paper, as the high lights should be fairly dense, and the deep shadows nearly clear glass.
Time for complete development should always be allowed; with a hot bath fifteen seconds will be sufficient, but if a cooler development is used, or the prints are solarized in the shadows, more time should be allowed. When the deep shadows are solarized, or appear lighter than surrounding parts, a hot and prolonged development is required to obtain sufficient blackness, as they have a tendency to look like brown paper. I have found breathing on solarized shadows useful, as in the presence of slight moisture they begin to print out and become dark before development, getting black almost directly the print is floated on the oxalate. Three or four acid baths of about ten minutes each are used, and the prints are washed as before. The process throughout takes much less time than silver printing, and can be kept on all the winter, when it is nearly impossible to print in silver. Prints can be developed in weak daylight or gaslight, and prolonged washing is dispensed with.—N.P. Fox, reported in Br. Jour. of Photo.
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A communication to the North London Photographic Society.
A communication to the North London Photographic Society.
[Continued fromSupplement, No. 706, page 11283.]
In the first part of this paper were described certain forms of silver; among them a lilac blue substance, very soluble in water, with a deep red color. After undergoing purification, it was shown to be nearly pure silver. During the purification by washing it seemed to change somewhat, and, consequently, some uncertainty existed as to whether or not the purified substance was essentially the same as the first product; it seemed possible that the extreme solubility of the product in its first condition might be due to a combination in some way with citric acid, the acid separating during the washing. Many attempts were made to get a decisive indication, and two series of analyses, one a long one, to determine the ratio between the silver and the citric acid present, without obtaining a wholly satisfactory result, inasmuch as even these determinations of mere ratio involved a certain degree of previous purification which might have caused a separation.
This question has since been settled in an extremely simple way, and the fact established that the soluble blue substance contains not a trace of combined citric acid.
The precipitated lilac blue substance (obtained by reducing silver citrate by ferrous citrate) was thrown on a filter and cleared of mother water as far as possible with a filter pump. Pure water was then poured on in successive portions until more than half the substance was dissolved. The residue, evidently quite unchanged, was, of course, tolerably free from mother water. It was found that by evaporating it to dryness over a water bath, most of the silver separated out as bright white normal silver; by adding water and evaporating a second time, the separation was complete, and water added dissolved no silver.The solution thus obtained was neutral.It must have been acid had any citric acid been combined originally with the silver. This experiment, repeated with every precaution, seems conclusive. The ferrous solution, used for reducing the silver citrate, had been brought to exact neutrality with sodium hydroxide. After the reduction had been effected, the mother water over the lilac blue precipitate was neutral or faintly acid.
A corroborating indication is the following: The portions of the lilac blue substance which were dissolved on the filter (see above) were received into a dilute solution of magnesium sulphate, which throws down insoluble allotropic silver of the form I have called B (see previous paper). This form has already been shown to be nearly pure silver. The magnesia solution, neutral before use, was also neutral after it had effected the precipitation, indicating that no citric acid had been set free in the precipitation of the silver.
It seems, therefore, clear that the lilac blue substance contains no combined citric acid. Had the solubility of the silver been due to combination with either acid or alkali, the liquid from which it was separated by digestion at or below 100° C. must have been acid or alkaline; it could not have been neutral.
We have, therefore, this alternative: In the lilac blue substance we have either pure silver in a soluble form or else a compound of silver, with a perfectly neutral substance generated from citric acid in the reaction which leads to the formation of the lilac blue substance. If this last should prove the true explanation, then we have to do with a combination of silver of a quite different nature from any silver compounds hitherto known. A neutral substance generated from citric acid must have one or more atoms of hydrogen replaced by silver. This possibility recalls the recent observations of Ballo, who, by acting with a ferrous salt on tartaric acid, obtained a neutral colloid substance having the constitution of arabin, C6H10O6.
To appreciate the difficulty of arriving at a correct conclusion, it must be remembered that the silver precipitate is obtained saturated with strong solutions of ferric and ferrous citrate, sodium citrate, sulphate, etc. These cannot be removed by washing with pure water, in which the substance itself is very soluble, but must be got rid of by washing with saline solutions, under the influence of which the substance itself slowly but continually changes. Next, the saline solution used for washing must be removed by alcohol. During this treatment, the substance, at first very soluble, gradually loses its solubility, and, when ready for analysis, has become wholly insoluble. It is impossible at present to say whether it may not have undergone other change; this is a matter as to which I hope to speak more positively later. It is to be remarked, however, that these allotropic forms of silver acquire and lose solubility from very slight causes, as an instance of which may be mentioned the ease with which the insoluble form B recovers its solubility under the influence of sodium sulphate and borate, and other salts, as described in the previous part of this paper.
The two insoluble forms of allotropic silver which I have described as B and C—B, bluish green; C, rich golden color—show the following curious reaction. A film of B, spread on glass and heated in a water stove to 100° C. for a few minutes becomes superficially bright yellow. A similar film of the gold colored substance, C, treated in the same way, acquires a blue bloom. In both cases it is the surface only that changes.
Sensitiveness to Light.—All these forms of silver are acted upon by light. A and B acquire a brownish tinge by some hours' exposure to sunlight. With C the case is quite different, the color changes from that of red gold to that of pure yellow gold. The experiment is an interesting one. The exposed portion retains its full metallic brilliancy, giving an additional proof that the color depends upon molecular arrangement, and this with the allotropic forms of silver is subject to change from almost any influence.
Stability.—These substances vary greatly in stability under influences difficult to appreciate. I have two specimens of the gold yellow substance, C, both made in December, 1886, with the same proportions, under the same conditions. One has passed to dazzling white, normal silver, without falling to powder, or undergoing disaggregation of any sort; the fragments have retained their shape, simply changing to a pure frosted white, remaining apparently as solid as before; the other is unchanged, and still shows its deep yellow color and golden luster. Another specimen made within a few months and supposed to be permanent has changed to brown. Complete exclusion of air and light is certainly favorable to permanence.
Physical Condition.—The brittleness of the substances B and C, the facility with which they can be reduced to the finest powder, makes a striking point of difference between allotropic and normal silver. It is probable that normal silver, precipitated in fine powder and set aside moist to dry gradually, may cohere into brittle lumps, but these would be mere aggregations of discontinuous material. With allotropic silver the case is very different, the particles dry in optical contact with each other, the surfaces are brilliant, and the material evidently continuous. That this should be brittle indicates a totally different state of molecular constitution from that of normal silver.
Specific Gravities.—The allotropic forms of silver show a lower specific gravity than that of normal silver.
In determining the specific gravities it was found essential to keep the sp. gr. bottle after placing the material in it for some hours under the bell of an air pump. Films of air attach themselves obstinately to the surfaces, and escape but slowly even in vacuo.
Taken with this precaution, the blue substance, B, gave specific gravity 9.58, and the yellow substance, C, specific gravity 8.51. The specific gravity of normal silver, after melting, was found by G. Rose to be 10.5. That of finely divided silver obtained by precipitation is stated to be 10.62.1
I believe these determinations to be exact for the specimens employed. But the condition of aggregation may not improbably vary somewhat in different specimens. It seems, however, clear that these forms of silver have a lower specific gravity than the normal, and this is what would be expected.
Chestnut Hill, Philadelphia, May, 1889.—Amer. Jour. of Science.
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