NEW SYSTEM OFCHEMICAL PHILOSOPHY.CHAP. V.
NEW SYSTEM OFCHEMICAL PHILOSOPHY.
CHAP. V.
Allthe metals are disposed to combine with oxygen, but the combination is effected more easily with some than with others; the compound is usually called anoxide, but in some instances it is also called anacid. The same metal combines with one, two, or perhaps more atoms of oxygen, forming compounds which may be distinguished according to Dr. Thomson, by the termsprotoxide,deutoxide,tritoxide, &c.
Such however is the repulsion of oxygen to oxygen that we rarely find three atoms of it retained by a single atom of any kind; and there arenot many instances of metals capable of holding two atoms of oxygen. Various modifications of the proportions of metals and oxygen arise from the combinations of the oxides themselves one with another and with oxygen, so as to lead some to imagine that an atom of metal in some instances combines with 3, 4, or more of oxygen. This is altogether improbable: It is much more simple to suppose that one atom of oxygen connects two or more atoms of protoxide, 1 of protoxide unites to 1 or more of deutoxide, &c. These intermediate oxides are in few if any instances found to combine with acids like the other two oxides.
There is no reason that I am acquainted with for disbelieving that oxygen combined with a metal is still repulsive of oxygen, and that by the same law as particles of an elastic fluid; that is, the repulsion is inversely as the distance of the centres of the atoms. Hence it may be demonstrated that it requires twice the strength of affinity to form a deutoxide as a protoxide, three times the strength to form a tritoxide as a protoxide, &c. On this account it is, in all probability, that deutoxides are not numerous, and tritoxides are rarely if ever found.
The quantity of oxygen that combines with any metal to form an oxide may be investigated by several methods.
1st. By combustion; a given weight of the metal may be burned and the oxide produced may be collected and weighed; when the increase by combustion will appear.
2. By solution in an acid and precipitation by an earth or alkali; in this case a given weight of the metal is dissolved and precipitated; the precipitate collected and sufficiently dried shews the increase by oxygen.
3. By transferring the oxygen from an oxide to another metal; in this case the metal in question is usually immersed in a saline solution of the other metal; this latter metal gives up its oxygen to the former and is itself reformed orrevivedas it is termed.
4. By determining the proportion of hydrogen gas evolved during the solution of a given weight of metal; then allowing half of that volume for its equivalent of oxygenous gas, the weight of it shews the oxygen united to the metal; it being now well understood that water furnishes the two elements of hydrogen and oxygen in such case.
5. The higher oxides are conveniently determined by the application of the solution of oxymuriate of lime to the lower oxides in solution.
6. The quantity of oxygen in several oxides may be found from the quantity of nitrous gas evolved during the solution of a given weight of metal in nitric acid.
The first four methods have been used by chemists for several years past; the two last I have added from my own experience, having found them very useful assistants in various instances. The last method by nitrous gas, has indeed been proposed before, and labour bestowed on it both by others and myself, but without reducing the results to any certainty, till lately; the principal cause of this want of success has arisen from misunderstanding the nature and constitution of nitric acid. Most chemists seem with me to have mistakennitrousacid fornitric; the former is composed of 1 atom of azote and 2 of oxygen; or perhaps of 2 azote and 4 oxygen; the latter of 2 azote and 5 oxygen, or 2 nitrous gas and 3 oxygen; the weight of the former is 19, or its double 38, on my scale, and that of the latter 45. [My reasons for adopting the above conclusion respecting nitrous acid, which is at variance with that inVol. 1, p. 331, will be given hereafter.] When therefore a metal is oxidized by nitric acid, 3 atoms of oxygen (= 21) go to the metal, and 2 atoms of nitrousgas (= 24) are disengaged. Hence ⅞ of the weight of nitrous gas evolved is the weight of oxygen combined. It sometimes happens however that the nitrous gas is partly or wholly retained by the residue of nitric acid; but in this case the oxymuriate of lime can be applied to convert the nitrous gas into nitric acid, and from the oxygen imbibed the quantity of nitrous gas may be inferred.
Some difficulties have been found in ascertaining both the number and proportions of the oxides of gold; hence the differences in the results of authors.
Gold does not burn by exposure to heat, but gold leaf and gold wire may be deflagrated by electricity and galvanism; a purple powder is the product, which is considered by some as the protoxide of gold; but others, after Macquer and Proust, conceive with greater probability that this powder is nothing but gold reduced to its ultimate division. Solutions of gold which are of a fine yellow, give a purple stain; and gold deoxidized by green sulphate of iron is precipitated blue, which precipitate gradually assumes a yellow colour as the particles becomeunited. The very weak affinity of gold for oxygen is shewn by the difficulty with which it is oxidized and the ease with which the oxygen is expelled again by heat; these facts seem to preclude the idea of gold combining with oxygen in high temperatures.
Protoxide.Gold is scarcely affected by pure sulphuric, nitric or muriatic acid; but it is easily oxidized and dissolved by nitro-muriatic acid (that is, a mixture of nitric and muriatic acids) when assisted by a temperature of 150 or 200°. Caustic potash being put into the solution and heated, a brownish black precipitate is obtained; but a part of the oxide remains in solution combined with the muriate of potash, according to Vauquelin; and Proust has observed that the oxide cannot be washed and dried in a moderate heat without a portion of the gold being revived; hence the difficulty of ascertaining in this way the weight of oxygen combining with gold.
I have succeeded, as I apprehend, in determining the relative weights of gold and oxygen, by two methods, which mutually corroborate each other. The first is by means of the nitrous gas generated by the solution of gold; and the second is, by finding what quantity of greenoxide of iron is converted into red by precipitating a given weight of gold in solution.
Ten grains of guinea gold of the sp. gr. 17.3, were repeatedly dissolved in a small excess of nitro-muriatic acid; the quantity and purity of the nitrous gas generated were duly observed and allowance made for the loss occasioned by a small portion of common air originally in the gas bottle. The volume of nitrous gas corrected as above was always found between 1100 and 1200 grain measures, the weight of which may be estimated at 1.6 grains, corresponding to 1.4 grains of oxygen. The small portion of alloy (¹/₁₂) known to be in standard gold is chiefly copper with a small part silver; now it will be seen in the sequel that copper takes ¼ of its weight of oxygen; hence if we allow .8 of a grain for copper and .2 for the oxygen combining with it, we shall have 9.2 gold united to 1.2 oxygen, or 100 gold with 13 oxygen, which is nearly the same as Berzelius has determined by precipitating the gold by mercury.—Again, 10 grains of gold were dissolved as above (= 9.2 pure) and precipitated by a solution of pure green sulphate of iron of the sp. gr. 1.181 and which I had previously proved to contain 9 grains of green oxide in 100 measures. They converted 120 measures ofthis green sulphate into yellow, which was carefully precipitated afterwards by lime water, dried and weighed. The gold precipitated was found very nearly 9 grains; and the yellow oxide of iron mixed with oxide of copper was nearly 13 grains. Now 120 measures sulphate iron contain 10.8 grains green oxide, and these require ¹/₉ of their weight of oxygen (see the oxides of iron) to be changed into yellow oxide, or 1.2 oxygen. Hence it appears that the oxygen combined with the gold was transferred to the iron unchanged in quantity. It is to be observed however that green oxide of iron not only deoxidates the gold but it semideoxidates the copper also; so that .1 of the transferred oxygen above might be said to be derived from the copper, and the rest, or 1.1 from the 9 grains of gold; this would give 100 gold to 12.2 oxygen, which is still nearer to the determination of Berzelius. Upon the whole I am inclined to adopt the proportion of 8 to 1 or 100 to 12.5 as that which appears the most correct approximation and at the same time a ratio easily remembered and adapted to facilitate calculations.
We are now to consider whether the above is the protoxide. As no other oxide has been clearly shewn to exist, and as this combines withmuriatic acid, with ammonia, with the oxide of tin, &c. and is wholly deoxidated by green sulphate of iron and by a moderate heat, there seems every reason to conclude it is a combination of the most simple kind, or 1 atom of metal to 1 of oxygen. Hence the atom of oxygen being 7, that of gold must be 56, and not 140 or 200, as statedVol. 1, p. 250.
Berzelius seems to consider the above as the tritoxide, or three atoms of oxygen to one of gold; but it is extremely improbable that gold, which is allowed to have a weak affinity for oxygen, should be able to restrain the violent repulsion of three atoms of oxygen, and should on every occasion lose them all at once, and not by degrees, as is usual with other high oxides.
Subjoined are the results of various authors in regard to the oxide of gold, but generally given with diffidence as to their accuracy.
Since writing the above I have had an opportunity of repeating the experiments on the oxide of gold by an improved nitrous gas apparatus, calculated almost entirely to exclude atmospheric air; I find less nitrous gas produced during the solution than stated above, sometimes by ⅓, and that it is variable according to the excess of nitric acid; also that the solution requires a portion of oxymuriatic acid as an equivalent for the nitrous gas retained. I prefer, however, the method of oxidizing the green sulphate of iron; by putting a small excess of the green sulphate and precipitating, first the red oxide and then the green, I obtained very distinct results. On the whole I am inclined to think my results preceding these have rather overrated the oxygen, and that it would as nearly be stated at 11 on the hundred. This would be nearly a mean of those in the above table, and would require the atom of gold to be 63, and that of the oxide 70. Between the two extremes of 56 and 63 it is most probable the true weight of the atom of gold will be found.
It may be proper to add that I have found 100 grain measures of muriatic acid (1.16), and 25 of nitric (1.35), are sufficient todissolve 40 grains of standard gold; and I have reason to think the acids are in due proportion nearly, though different from what is usually recommended and employed.
Platina exhibits greater difficulties than gold in the investigation of its compounds with oxygen. It is not oxidized by heat; but by the explosion of an electric battery it is converted into a black powder, which is most probably the metal in extreme division, though it has been considered by some as the protoxide. Platina is capable of being oxidized and dissolved by nitro-muriatic acid, but less easily than gold; it requires more acid, as high or higher temperature and long continued digestion; nitrous gas is given out, during the solution, but sparingly. When lime or an alkali is added to the solution with a view to precipitate the oxide, a triple compound is usually formed of the acid, the oxide and the alkali, which is in most instances precipitated. This weighty compound renders the valuation of the oxygen in it very uncertain.
Chenevix has made some observations on the oxides of platina, (see Nichols. Journ. 7. p. 178.) He finds two oxides: the one consists of 93platina and 7 oxygen; the other of 87 platina and 13 oxygen; but the experiments on which these results rest are not quite satisfactory.
Mr. E. Davy in the 40th vol. of the Philos. Magazine, states his having reduced the oxide of platina in solution by means of hydrogen; and that he finds the oxide to consist of 84 platina and 16 oxygen nearly. I could not succeed at all in effecting the reduction of the metal in this way.
Berzelius has lately given us the results of his investigation on this subject. (An. de Chimie 87—126.) According to this distinguished chemist there are two oxides of platina; the first consists of 100 metal and 8¼ oxygen, and the second of 100 metal and 16½ oxygen, nearly. In order to understand his process it may be proper to premise that when nitro-muriatic acid has dissolved as much platina as it can, there is still a great excess of one or both of the acids, which is unnecessary for the existence of the solution, and which may, and in general ought to be expelled by evaporation; by exposing the solution to a heat of 100 or 150° the excess of both acids is in great part driven off and a dry red mass is obtained, without smell, but very deliquescent. It is equal to or rather more than twice the weight of theplatina. It consists of water, muriatic and nitric acids, oxygen and platina; it is still an acid salt. By exposing the dry mass again to a heat of 400 or 500°, it liquifies, exhales acid fumes having the odour of oxymuriatic acid, and becomes again a dry mass of an olive colour, exhaling fumes as the heat increases, and loses about ¼ of its weight. It is still soluble in water, except a few atoms of black powder, continues acid to the tests, and may be considered as a supermuriate of platina. If this olive powder be again heated almost to red, it exhales a visible smoke in the open air, which has the smell of oxymuriatic acid, and becomes a light brown powder, having lost a little weight. It is then neither deliquescent nor soluble in water except in a small degree so as to give the yellow colour. In this state it has been considered as a neutral muriate. By a moderately bright red heat this powder is decomposed and leaves a black spongy mass which is found to be pure platina.
The insoluble muriate of platina according to Mr. E. Davy, contains 72.5 per cent. of platina, and Berzelius finds 73.3; the loss is considered as oxymuriatic acid; hence from the known proportions of this acid Berzelius infers the constituents of 100 muriate = 73.3platina, 6.075 oxygen and 20.625 muriatic acid; or 100 platina take 8.3 oxygen. The near agreement of the above authors is favourable to the accuracy of their results; but I have found some difficulty in obtaining the insoluble muriate free from the soluble one, and at the same time from reduced platina because the precise degree of heat requisite to produce it is neither well known nor easily attained; and it is desirable that a certain weight of platina should be dissolved and the same weight reproduced as a confirmation of accuracy. From a train of experiments on the soluble and insoluble muriates of platina, the salts being obtained from the purified laminated metal, I am disposed to consider the above results as good approximations to the truth.
In order to obtain the other oxide, Berzelius digests mercury in a solution of the supermuriate of platina; a black powder is thrown down, which is found to be platina, and mercury is taken up, being oxidized at the expence of the platina. It was found that 16.7 grains of mercury had precipitated 8.5 of platina; and the mercury being calculated as in the state of deutoxide, contained, from the known proportions of this metal, 1.4 oxygen; hence 8.5 platina must have yielded 1.4 oxygen; andif 8.5 ∶ 1.4 ∷ 100 ∶ 16.4; so that 100 platina must have had 16.4 oxygen in the supermuriate, or twice the quantity it had in the insoluble muriate.
This conclusion appears to me premature; the mercurial oxide should at least have been precipitated and a corresponding quantity have been found and proved to be the red oxide. Even had this been the case, it is not easy to determine what quantity of it might be due to the residue of nitro-muriatic acid. But I have not found that the common yellow or red oxide of mercury is precipitated by lime water in such case; the precipitate is brown, and evidently contains both mercury and platina. Proust had found in his excellent essay on platina (Journ. de Physique 52—437, 1801) that mercury decomposes muriate of platina, that an amalgam of platina with a little calomel, and much mercury in powder, were precipitated; exposed to heat, a fine black powder was left which had the characters of platina. Into a solution of pure platina that had been evaporated to dryness in 150° and redissolved, I put 9¼ grs. of mercury, and boiled it for 10 minutes in a glass capsule, till there was apparently no further change; the liquor filtered was as yellow as at first; the mixture of black powder andrunning mercury remaining on the filter, when dried, weighed 6½ grains; this heated to a low red in an iron spoon, left 1 grain of fine black powder; the liquid saturated with lime water, yielded 2½ grains dry black powder insoluble in cold nitric acid; after this, protomuriate of tin threw down 5¾ grains of the compound oxides of platina and tin. The solution at first contained 3.3 grains of platina.
In another experiment 2 parts of calomel were put to 1 of platina in solution; when heated to boiling, the calomel was dissolved and a little black powder was precipitated, which did not amount to half the weight of the platina. Lime water threw down from the liquid, a yellowish olive or brown precipitate, partially soluble in cold nitro-muriatic acid; and after this, muriate of tin yielded a brown precipitate. These experiments shew that the action between muriate of platina and mercury or the mercurial salts, is of a complicated nature, and is not limited to the decomposition of the oxide of platina and the substitution of the deutoxide of mercury in its place.
The difficulties abovementioned have led me to investigate the oxygen combining with platina by means of the nitrous gas yielded upon itssolution in nitro-muriatic acid. By three distinct experiments I found that 10 grains of pure platina by solution yielded nearly 750 grain measures of nitrous gas, which may be considered as 1 grain in weight; ⅞ of which = .875 for oxygen; this would give 8.75 oxygen per cent. But from a subsequent experiment made under circumstances calculated to preclude as much as possible every source of fallacy, I obtained 790 measures of nitrous gas from 10 grains of platina; and the solution afterwards took 60 measures of oxymuriatic acid gas before a permanent smell of the gas was produced. These 790 measures = 1.05 grain, ⅞ of which = .92, to which add .04 for the oxygen acquired from the oxymuriatic acid, and we have .96 oxygen for 10 platina; or 100 platina take 9.6 oxygen. But if 9.6 ∶ 100 ∷ 7 ∶ 73, for the weight of an atom of platina, and 80 for that of the protoxide, as I apprehend it to be, and the only oxide of platina we can at present form. (The atom of platina in Vol. 1, page 248, was estimated at 100.)
When silver wire is exploded by electricity in oxygen gas, a black powder is produced, which is the oxide of silver. If silver bedissolved in nitric acid and precipitated by lime water, an olive brown powder falls which becomes black when exposed to the light. This black powder is the only oxide of silver with which we are acquainted. The proportion of silver and oxygen has been investigated by various chemists; the results are as under.
From the solution of 170 grains of standard silver I obtained nearly 30 oz. measures of nitrous gas = 18½ grains, corresponding to 16 oxygen. This would give 9.4 oxygen upon 100 silver. But as ⅒ of the metal or 17 grains was copper, and this takes ¼ of its weight of oxygen, we shall have 159 silver and 11¾ oxygen, or 100 silver and 7.7 oxygen nearly.
If we adopt 7.8 as the proper quantity of oxygen on 100 silver, we shall have 7.8 ∶ 100 ∷ 7 ∶ 90 nearly, which represents the weight of an atom of silver, and 97 that of the oxide.
Two oxides of mercury have been long known and are well distinguished from each other. They may be obtained by exposing mercury to a heat not exceeding 600°, in contact with oxygen gas or atmospheric air, and due agitation; but this method is rarely adopted in practice. A high degree of heat decomposes the oxides again.
Protoxide.To obtain the protoxide, mercury must be slowly dissolved in dilute nitric acid without heat, and an excess of mercury must be used. If to 1000 grain measures of nitric acid, 1.2 sp. gr. be put 500 grains of mercury, by occasional agitation the requisite solution will be obtained in 24 hours. A portion of this solution must be treated with a small excess of lime water or caustic alkali, when a black powder will be thrown down, which is the oxide containing a minimum of oxygen, and hence may be considered the protoxide.
Deutoxide.If to 1000 measures of nitric acid, 1.2 sp. gr. be put 350 grains of mercury, and the mixture be boiled till the mercury disappear, a solution will be obtained containing the deutoxide. A portion of this being treated as beforementioned with lime water, ayellowish red powder is precipitated, which is the oxide of mercury containing a maximum of oxygen; all the later authors agree that it contains just double the quantity of oxygen to a given portion of mercury that the former does, and may therefore be called the deutoxide.
These two oxides combine with most acids and form salts, some of which exhibit remarkable differences occasioned by the oxides; thus, muriatic acid with the protoxide forms protomuriate of mercury, commonly calledcalomel, an insoluble salt; with the deutoxide it forms deutomuriate of mercury, commonly calledcorrosive sublimate, a soluble salt.
The proportions of metal and oxygen in the two oxides may be found by precipitating a known weight of mercury reduced by solution to either of the oxides, then drying and weighing the oxides, when the increase of weight by the addition of oxygen may be observed. This method is less accurate with regard to mercury than to other metals, on account of the very great weight of the atom, by which a small error in the gross weight of the oxide will be a great one as it respects the oxygen. This circumstance will partly account for the differences of authors on this subject.
One fact has been for some time known which demonstrates the oxygen in the red oxide to be double that in the black. Corrosive sublimate may be reduced to calomel by adding to it as much mercury as the sublimate contains, and triturating the mixture well, the oxygen of the red oxide (as well as the acid) becomes equally divided amongst the mercury and forms the black oxide, which is a constituent of calomel. Hence it follows that if the oxygen in one oxide can be ascertained, that of the other becomes known. Or if we can find how much oxygen must be added to the black oxide to change it to the red, we shall know the oxygen in both. Conformably with this last idea I have found a very accurate and elegant method of ascertaining the oxygen required to convert the black to the red oxide by treating protomuriate of mercury, mixed with water and a little muriatic acid, with oxymuriate of lime in solution; this must be gradually added till the protomuriate is dissolved, or rather converted to the deutomuriate. The quantity of oxygen in a given solution of oxymuriate of lime is most conveniently found by a solution of green sulphate of iron, as will be shewn under the oxides of that metal.
The oxides of mercury may be investigated by the nitrous gas produced during solution. When mercury is dissolved without heat, as mentioned above, no nitrous gas is liberated. The solution has a strong nitrous smell and requires a great quantity of oxymuriate of lime to saturate both the oxide and the acid. When heat is employed to accelerate the solution, nitrous gas is liberated. I dissolved 154 grains of mercury in nitric acid, 1.2 sp. gr., by the application of a gentle heat from a lamp. About ⅒ excess of acid remained in the solution; the nitrous gas obtained was 12 oz. measures = 7.5 grains, corresponding to 6.5 oxygen, which gives nearly 4 oxygen or 100 mercury. This would have led me to suppose I had obtained theblackoxide in solution; it was however entirely thered, as it gave no precipitate by common salt, and exhibited the red oxide by lime water; but it required as much oxymuriate of lime as contained 6.5 oxygen to saturate thenitrous gasin the solution before any oxymuriatic acid was liberated. It was clear therefore that only ½ of the nitrous gas was evolved, and the other ½ was retained in the solution, though it had been exposed to boiling heat.
The following are the proportions assigned by the several authors for the oxides of mercury.
Though the relative weights of oxygen and mercury may be investigated as above, yet it is from the weight of mercury and the acids in the salts of mercury, some of which are of a very definite character, such as the muriate and the deutomuriate, that the relative weight of the atom of mercury is best investigated. From these I first deduced the weight of an atom of mercury to be 167 about 10 years ago, and subsequent experience has not induced me to change the number, though it probably may admit of some correction. If the atom of mercury bedenoted by 167, that of the protoxide will be 174, and that of the deutoxide 181; which makes 100 mercury take 4.2 and 8.4 oxygen for the oxides respectively, as in the above table.
The discoverer of this metal, Dr. Wollaston, has given us its distinguishing chemical properties; but we are indebted to Berzelius and Vauquelin for the proportions of oxygen and sulphur which combine with the metal (Vid. Annal. de Chimie, 77 and 78.) Few chemists have had an opportunity of making experiments on this metal, owing to its great scarcity and the consequent high price of it (1 shilling per grain). It does not seem desireable that any but those skilled in the more delicate chemical manipulations should operate upon articles such as the present.
Berzelius treated the muriate of palladium with mercury, which abstracted the oxygen and left an amalgam of palladium and mercury; from the quantity of mercury dissolved he calculates that 100 palladium combine with 14.2 oxygen. This conclusion was corroborated by the circumstance that 100 palladium were found to take 28 of sulphur, or double the quantity of oxygen, which frequently happens with the metals.
Vauquelin precipitates the oxide of palladium from the muriate by potash; it appears of a red brown colour, and is probably a hydrate; when washed and dried in a moderate heat, it becomes black, it loses 20 per cent. by a red heat and becomes metallic. This would give 25 oxygen on 100 metal; but as he finds the sulphuret to be 100 metal with 24 or 30 sulphur, nearly agreeing with Berzelius, it is very probable that a moderate heat does not free the oxide from water, and that consequently a part of the 20 per cent. loss is water.
I dissolved 3 grains of palladium in a small excess of nitro-muriatic acid and obtained 240 grain measures of nitrous gas; the same quantity was obtained a second time, and to the solution (slightly acid) were added by degrees 200 measures of oxymuriatic acid gas; after agitation no smell was perceived, but by increasing the quantity of gas a permanent smell of oxymuriatic acid was produced, and when 200 more had been added the smell was sensible for some days in an open jar, a presumption that no higher oxide is to be obtained. Now 240 nitrous gas = .32 of a grain, corresponding to .28 of oxygen, and 200 oxymuriaticacid = .64 of a grain, corresponding to .15 oxygen; the sum of the two portions of oxygen = .43, which must have combined with 3 grains of palladium; if .43 ∶ 4 ∷ 7 ∶ 50 nearly. Or 100 metal combine with 14 oxygen, as determined by Berzelius. I find the sulphuret to accord with this determination; and by carefully saturating the excess of acid in the nitro-muriate of palladium and then finding the quantity of lime water necessary to precipitate a certain weight of palladium, as well as the quantity of test muriatic acid necessary to dissolve the precipitated oxide, I am confirmed in the opinion that the atom of palladium must weigh 50 nearly, and its oxide 57, which there is every reason to believe is the protoxide.
Nothing certain has yet been determined respecting the oxygenation of these very rare metals.
There are two oxides of copper according to the results of Proust, Chenevix, Berzelius and others, the proportions of which are givennearly the same by all, and so as to leave no reasonable doubt concerning their accuracy.
1.Protoxide.This oxide isorange, and contains 12½ oxygen on 100 copper: it is obtained by precipitating a portion of copper from the solution of any cupreous salt, by means of iron, then mixing this copper with a rather greater portion of the deutoxide and triturating them well. This being done, the mixture is to be dissolved in muriatic acid, and the orange oxide may then be precipitated by an alkali.
2.Deutoxide.This oxide isblack; it contains 25 oxygen on 100 copper: theblackoxide is obtained by dissolving copper in nitric or sulphuric acid, then precipitating by lime water or an alkali, and heating the dried precipitate red hot. It may also be obtained by exposing copper to a red heat for some time in common air or oxygen gas, removing the scales and exposing them in like manner, till at length the black oxide is formed.
By dissolving 112 grains of copper turnings in 1000 grain measures of 1.16 nitric acid, I obtained 48 oz. measures of nitrous gas, = 30 grains; by oxymuriate of lime I found 2 grains of nitrous gas in thesolution, making in all 32 grains = 28 grains of oxygen. If 28 ∶ 112 ∷ 14 ∶ 56, for the weight of an atom of copper; hence the protoxide = 63 and the deutoxide = 70. These weights I adopted in 1806, and have not seen any reason to modify them since.
Two well known and well distinguished oxides of iron are now universally admitted; the one contains 28 oxygen on 100 iron, the other 42 on 100.
1.Protoxide.This is always formed when iron is dissolved in dilute sulphuric or muriatic acid; it may be precipitated from these solutions by the pure alkalies or earths; it appears at first of a dark green, being then a hydrate or combined with water; on a filtre it soon becomes yellow at the surface by attracting oxygen; when dried in a heat of 200° or upwards it becomes black. The quantity of oxygen in it is best ascertained from the hydrogen generated during the solution of the iron. All the authorities I have found nearly concur in their results as under.
100 grains of iron dissolved in dilute sulphuric or muriatic acids yield hydrogen, according to
By precipitating the oxide, and drying it, nearly the same result may be obtained, as 100 iron will yield 128 oxide. This oxide is magnetic.
2.Intermediate or red oxide.This oxide may be obtained in various ways. First by calcining the sulphate or nitrate of iron. Second by precipitation from old solutions of the salts of iron; the precipitate isyellowat first, being perhaps a hydrate; but when dried and heated it becomes brown-red. Third, by calcining iron or repeatedly exposing iron filings to a red heat, and trituration. Fourth, by treating a solution of the sulphate or other salt of the protoxide with oxymuriatic acid, or oxymuriate of lime till oxymuriatic acid is evolved; then precipitating the oxide which is thus convertedinto the red. Fifth, by agitating water containing the green oxide recently precipitated, with oxygen gas. The red oxide is not sensibly magnetic.
The quantity of oxygen in the red oxide may be investigated in various ways, and it is generally allowed that they all concur in giving 42 on 100 iron. The one which I have used peculiarly, and prefer both for ease and accuracy, is to find the quantity of oxymuriatic acid gas necessary to saturate a given portion of the green sulphate. I take for instance 100 measures of 1.149 green sulphate, which I know to contain 8 grains of black oxide; this I find absorbs nearly 13 hundred measures of oxymuriatic acid gas before the acid smell is developed; the oxygen corresponding to this quantity of acid is known to be near 660 measures, = .88 grain. (SeeVol. 1, p. 308.) Hence, if 8 ∶ .88 ∷ 128 ∶ 14; or 128 black oxide acquire 14 or become 142 when converted into the red oxide. This fact being established, I find it very convenient to make use of the oxymuriate of lime instead of the acid gas, adopting the solution of green sulphate of iron as a test of the quantity of oxymuriatic acid in a given volume of any solution of oxymuriate of lime.
The quantity of oxygen in the red oxide of iron may be inferred, but not so satisfactorily, from the nitrous gas obtained during the solution of iron in nitric acid. In order to obtain the most gas from a given quantity of the materials, they should be so proportioned as to produce saturation nearly. If an excess of acid be used, it absorbs the nitrous gas in part; and if an excess of iron, it is not all dissolved. I took 50 grains of iron filings and 600 measures of 1.15 nitric acid; these were put together in a gas bottle and by the assistance of a little heat a quantity of nitrous gas was obtained equal to 12 grains in weight, allowing the sp. gr. of the gas to be 1.04 (air being 1); all the iron was dissolved except a few atoms, and the solution was slightly acid; the whole of the oxide was red when precipitated by lime water. Now 50 grains of iron take 21 of oxygen to form the red oxide, and these correspond to 24 of nitrous gas, which is just twice the quantity obtained; one half of the gas generated then remains in combination with the iron, even when the constituents of the salt are proportioned so as to produce mutual saturation. I was in expectation that the quantity of nitrous gas retained might be converted into nitric acid by oxymuriate of lime, and hence might be determined; butin this I was disappointed. When oxymuriate of lime is added to the liquid, a pungent gas is liberated, the nature of which I have not determined. Thinking it might in part be owing to the iron, I transferred the acid to soda, by decomposing the nitrate of iron by the carbonate of soda; this nitrate of soda however, when treated with oxymuriate of lime, exhibited the same phenomenon as the nitrate of iron. When an acid is added the oxymuriatic acid itself is given out. These results will require further consideration. At present I am inclined to think the pungent gas is one atom of nitrous and one of oxygen or what I formerly considered as nitric acid. (SeeVol. 1, plate 4, fig. 27.)
Some authors have found as they conceive, other oxides of iron, containing less or more of oxygen than the above; thus Darso finds by calcination from 15 to 56 oxygen on 100, (Nicholson’s Journ.Vol.17); but there is great reason to believe that uncertainties must exist in his mode of experimenting sufficient to account for the anomalies observed. This author has suggested some doubt whether the oxygenous gas naturally contained in water has any effect on the salts with green oxide of iron. I have ascertained thatpoint by repeated experiments, and can assert that the oxygen in water immediately unites to the green oxide of iron to convert it into red, and that the green sulphate may be used as an accurate test of the quantity of oxygen in water. When pure green sulphate of iron is dropped into water and then the oxide precipitated by a gradual addition of lime water, it falls down yellow in proportion to the oxygen in the water, which may be increased 3 or 4 times by artificial impregnation. If the oxygen of the water be previously saturated with nitrous gas, then the oxide is wholly precipitated green.
Gay Lussac, in the 80thVol.of the Annal. de Chimie, asserts that an oxide of iron containing 37.8 oxygen upon 100 iron is always obtained when iron is burned in oxygenous gas, and still more effectually when iron is oxydized by water or steam. If this oxide exist in the proportions stated, it must be a compound of 1 atom of the protoxide and 2 of the red oxide, which would give 37.3 oxygen on 100 of iron.
From the above facts and observations it is evident the atom of ironmust be considered as weighing 25, (and not 50 as already given,Vol. 1, page 258); the protoxide is 32, and the intermediate or red oxide is 2 atoms protoxide and 1 of oxygen = 71.
1.Protoxide.It appears to be ascertained from the experiments of Proust (Journ. de Physiq. 63—442), Richter (Nichols. Jour. 12.), Tupputi (An. de Chimie 78.), and Rolhoff (An. of Philos. 3—335.), that the protoxide of nickel consists of 100 metal and from 25 to 28 oxygen. My experiments on the solution of nickel in nitric acid give me 14 grains nitrous gas, corresponding to 12 oxygen, in the solution of 44 grains of nickel; this gives 100 nickel to 27 oxygen, which I adopt as agreeing with the mean of the beforementioned results. This oxide may be obtained by precipitation from a solution of nitrate of nickel; it is at first white, being then a hydrate; when dried in a moderate temperature it becomes yellowish; after this, being heated to a cherry red, it loses from 20 to 24 per cent. of water and becomes of an ash grey colour: this is the only oxide of nickel soluble in acids, and must therefore be deemed the protoxide: hence we have 27 ∶ 100 ∷ 7 ∶ 26,nearly, for the weight of an atom of nickel; and not 25 or 50, as estimated at page 258.Vol. 1.
Intermediate oxide.Thenard discovered a second oxide of nickel by passing oxymuriatic acid through a solution of nickel and then precipitating; it is a black powder; when treated with sulphuric or nitric acid it gives out gas, being the excess of oxygen above the protoxide; but with muriatic acid it gives oxymuriatic acid gas. Rolhoff was induced to believe, but I do not know upon what evidence, that this oxide contained 1⅓ or 1½ times the oxygen of the protoxide. By means of oxymuriate of lime I find the protoxide recently precipitated, takes half as much oxygen as it had previously, to form the black oxide; and that it cannot be formed, like the red oxide of iron, by agitation with water mixed with common air. The white oxide treated with oxymuriate of lime becomes almost instantly blue, growing darker till it gradually passes into brown, and finally black in about half an hour. It contains 40 oxygen on 100 nickel, and is most probably constituted of 1 atom of oxygen holding 2 of protoxide together, more especially as it is not found in combination with acids. The method I prefer to procure the black oxide is to precipitate a known weight ofoxide by lime water; then pouring off the clear liquid, I put as much liquid oxymuriate of lime to the moist hydrate as contains ⅒ of the weight of the oxide of oxygen, and stir frequently for half an hour; the point of saturation is found when more oxide put to the clear liquid is not discoloured on one hand, and when more oxymuriate of lime does not affect the colour, but remains in the clear liquid on the other hand.
There are two oxides of tin, which have been carefully investigated by several chemists, and appear to be ascertained with great precision. The protoxide isgrey, and contains 13½ oxygen on 100 tin; thedeutoxideiswhite, and contains 27 oxygen on 100 tin.
1.Protoxide.There are two methods of obtaining the constitution of this oxide. The first is by dissolving a certain weight of tin filings in muriatic acid, precipitating by lime water or carbonated alkalies and drying the oxide in a moderate heat; this is liable to some uncertainty; the precipitate being ahydrate, requires to be exposed to heat to expel the water; but if the heat approaches to red, the oxide takes fire and is converted into thedeutoxide. The second method is to dissolve tin in muriatic acid and carefully collect the hydrogen gas evolved; this was first done by Mr. Cavendish, with his usual accuracy, and published in 1766; he found 1 oz. of tin yield 202 oz. measures of hydrogen gas. I have frequently tried this experiment and always found a proportional quantity, or very nearly 200 measures for each grain of tin. This mode of investigation appears to me unexceptionable. Now 200 hydrogen unite to 100 oxygen, and 100 grain measures of oxygen = .134 grain in weight; hence if .134 oxy. ∶ 1 tin ∷ 7 oxy. ∶ 52 nearly for the weight of an atom of tin, on the presumption this is the protoxide.
2.Deutoxide.This may be obtained by heating tin till it takes fire, and the produce of the combustion is the oxide required; but to ascertain the proportions of tin and oxygen two other methods are preferable; the one is to treat tin with nitric acid of the sp. gr. 1.2 to 1.4; a violent effervescence and great heat ensue and the tin is converted into a white powder. This being dried in 100° gives about 160 grains for 100 of tin. It consists of the deutoxide united to a little acid and water; these two may be driven off by a low red heat, and 127grains of the deutoxide remain in the state of a white powder. The other method is to treat a solution of the protoxide of tin with oxymuriate of lime till it is saturated; this will be found when 59 grains of the protoxide have acquired 7 grains of oxygen, or 113½ grains of the deutoxide have acquired 13½ grains of oxygen, which corroborates the result by the 1st method. This oxide containing just twice as much oxygen as the former, may justly be considered as the deutoxide. No higher oxide of tin has been obtained.
The two oxides, though both white when precipitated, may be distinguished from their different appearances; the first iscurdy, the second,gelatinous.
It may be proper to subjoin authorities for these oxides:
There are three oxides of lead now generally recognized, theyellow, thered, and thebrown, the proportion of oxygen in each of which has been investigated by several chemists whose results do not well accord with each other. I shall treat of them under the following names, namely theprotoxide, theintermediate oxides, and thedeutoxide, for reasons which will appear.
1.Protoxide.The yellow oxide of lead is the only one capable of forming salts with acids. Lavoisier found the oxygen of this oxide combined with 100 lead to be 4.47; Wenzel, 10; Proust, 9; Thomson, 10.5; Bucholz, 8; Berzelius, 7.7. This last accords best with my own experience; but it is chiefly from the other combinations of lead, that the weight of its atom as well as that of the protoxide are determined and confirmed, as lead forms several very definite compounds with acids, &c. The quantity of oxygen in the protoxide may be found by several methods, as under.
1st. By dissolving a given portion of the oxide in acetic acid, and precipitating the lead by another metal, as zinc; in this case theoxygen of the lead goes to the zinc which becomes dissolved, and from the loss of weight of the zinc and the proportion of oxygen in zinc oxide being previously known, and the weight of the precipitated lead being found, we have data for determining the oxide of lead. I took 200 measures of acetate of lead solution (1.142), which I knew contained 27 grains of oxide of lead; this being diluted with an equal volume of water, the lead was precipitated by a rod of zinc; in 6 hours anarbor saturniwas formed which was collected and well dried; it weighed 21¾ grains, and the zinc rod had lost 7 grains: care must be taken in performing this experiment that all the lead be not precipitated, otherwise the oxide of zinc begins to fall, and the result is uncertain. In the residuary liquid I got 4 grains of sulphate of lead by sulphuric acid. Here then we have the oxygen of 21¾ lead transferred to 7 zinc; but if 7 ∶ 21¾ ∷ 29 ∶ 90 nearly. Now it is known that 29 parts of zinc take 7 of oxygen, therefore 90 lead take 7 of oxygen, and the atom of lead = 90, and the protoxide 97.
I formerly stated the atom of lead 95.Vol. 1, page 260.
2. By dissolving 180 grains of lead in nitric acid in a small thincapsule, and heating it till the salt was quite dry, I got 288 grains of salt, weighed in the capsule; 36 grains of this salt yielded 24¼ yellow oxide by a low red heat = 22½ lead. This gives 90 lead to 7 oxygen.
3d. Again, 36 grains of the above salt, dissolved in water, precipitated by ammonia, and well washed on a filter, gave 23+ grains of oxide separated from the filter, and this had acquired 1 grain, making 24+ grains of oxide from the 22½ lead as before; the residue of liquid gave no signs of lead by hydrosulphuret of ammonia. The same quantity of salt precipitated by an excess of lime water gave only 22 grains of oxide; but hydrosulphuret of ammonia precipitated 2+ grains of sulphuret of lead from the clear liquid.
II.Intermediate oxide or oxides.Minium or red lead, &c. Minium is an article of commerce used as a pigment and for various other purposes. It is made by exposing the yellow or protoxide of lead finely pulverized to a low red heat in a current of air, and constantly stirring the oxide so as to expose fresh particles to the air. In two days the yellow oxide is converted into the red. Several authors observe that red lead usually contains 1, 2, or more grains per cent. of impurities insoluble in nitric and acetic acids; the specimen I usedhowever was so pure as not to leave more than ⅓ of a grain per cent. of insoluble matter after being heated red and treated with dilute nitric acid.
Some of the most remarkable properties of red lead are, 1st. It is never obtained in combination with any acid; 2d. It yields oxygen gas when exposed to a bright red heat or when treated with concentrated sulphuric acid, and is in both cases reduced to the protoxide; 3d. When treated with dilute nitric acid it is dissolved in part, but constantly leaves an insoluble brown residuum, which is the deutoxide, as will be shewn; the weight of the deutoxide obtained is by my experiments 20 per cent. and the part in solution is found to be the protoxide; 4th. When treated with muriatic acid, muriate of lead is formed and oxymuriatic acid given out; 5th. When treated with dilute acetic acid or cold concentrated acetic acid, ½ of the oxide is dissolved and the remainder is still red, its colour being rather improved; if concentrated acid be used and boiling heat applied, then ⅘ of the whole oxide is dissolved and ⅕ remains of brown oxide, the same as with nitric acid.
Some of the above facts are new, and may contribute to elucidate thismost curious oxide, which scarcely has a parallel. Proust is the only author I know who has given a plausible conjecture concerning the peculiar nature of this oxide. He supposes it a compound of the yellow and brown oxides. This I believe is the fact; but it will be found I apprehend to be a compound of 1 atom of oxygen with 6 of the yellow oxide, as will appear from what follows.
Respecting the quantity of oxygen in the red oxide, Lavoisier finds 9 oxygen to 100 lead, Thomson 13.6, and Berzelius 11.55. This last is partly from experience and partly from a supposed analogy, that the successive oxides of the same metal contain oxygen as 1, 1½ and 2 respectively; and having found (I believe) correctly, that the brown oxide contains just twice as much oxygen as the yellow, this ingenious and generally accurate author adopts the theoretic inference in this instance at least prematurely, and concludes the red oxide is the mean between the yellow and the brown. But we must appeal to experience.
It has already been stated that when red lead is exposed to heat, oxygen gas is given out, and it may be added, a small trace of water; and yellow oxide remains.
This experiment requires considerable skill. If too great a heat is used, a part of the lead is reduced or revived as it is termed; if too little heat, then a part of the red lead remains unaltered. In performing this experiment I use a small clean iron spoon to hold the red lead, and cover it by another iron spoon; the whole is then held by a pair of tongs in a red fire till the spoon exhibits a uniform moderate red, and some time after.
It is then withdrawn and cooled, and the oxide weighed. The average loss of weight is nearly 2 grains per cent. If only 1 grain or less, a considerable portion of red oxide remains mixed with the yellow; if 3 or more grains, then the margin of the oxide exhibits particles of lead amounting to ⅒, less or more, of the original weight; this can be easily separated from the oxide if necessary, but it is apt to adhere to the iron; when red oxide remains, it is so mixed with the yellow as not easily to be separated, but its quantity may be determined by nitric acid, which dissolves the yellow, and ⅘ of the red, leaving a residuum of brown oxide, from which the quantity of red is inferred. Now if the loss of weight of 100 red oxide be only 2 grains, and a partof that be water, it is impossible that 115.55 should lose 3.85 grains of oxygen, according to Berzelius. Another experiment, equally decisive of the question, is to determine the quantity of oxygenous gas to be obtained by heat or acids from a given weight of red lead. In one experiment made with great care, 500 grains of red oxide gave 6 grains of oxygenous gas by sulphuric acid; in another, 200 yielded 2½ grains. In order to vary the mode of determining the quantity of oxygen, into 210 measures of test green sulphate of iron solution, (1.156) = 16.8 green oxide, put 160 grains of minium; to this was added dilute muriatic acid more than sufficient for the minium: The oxymuriatic acid from the oxygen of the minium was instantly seized by the oxide of the iron, the whole of which was found by precipitation to be changed from green to red and an excess of oxymuriatic acid appeared. Now 16.8 oxide would require 1.86 oxygen to become red, which it must have acquired from 160 of red lead; or 100 red lead yielded 1.2 oxygen, the same proportion as by sulphuric acid. These experiments point out 1.2 oxygen in 100 red lead as the excess which converts the yellow to the red oxide. Were any doubt to remain on the subject, the experiment withnitric acid and red oxide will remove it. If the red oxide contained a mean of oxygen between the yellow and the brown, when it is treated with nitric acid more than 50 per cent. of brown oxide would be obtained instead of 20, which is contrary to all experience. It must be observed that Berzelius informs us he extracted the yellow oxide, mechanically mixed (as he conceives) with the red oxide, by digestion with dilute acetic acid; but he does not inform us how much per cent. his minium was reduced by this operation. From what is stated above, it appears that about ½ of the whole is thus dissolved. The remaining half would then contain double the quantity of oxygen and brown oxide per cent. that the original did. Still these quantities are inadequate to explain the phenomena. Besides it cannot be admitted that aredand ayellowpowder can be intimately mixed in equal quantities and the mixture not be distinguishable without difficulty from theredone, and be altogether different from theyellow. We must then conclude that the minium of commerce (such as I have used) is a true chemical compound.
Grounding our reasonings upon the preceding facts, there are but two suppositions that can be considered as plausible, respecting theconstitution of the red oxide. It may be 1 atom of oxygen and 5 of yellow oxide, or 1 atom of oxygen and 6 of yellow oxide. The former would give 1.4 per cent. extra oxygen in 100 red oxide, and 21 brown oxide; the latter would give 1.2 per cent. extra oxygen and 18 brown oxide. I adopt the latter supposition; because it agrees with experiment in regard to oxygen, and gives the brown oxide a littlelowerthan experiment, as may be expected on two accounts; first, the residue of brown oxide contains the insoluble dross of the red oxide (which was very small however, as stated above); and, second, unless a considerable excess of nitric acid be used, or long digestion, a small portion of the red oxide escapes decomposition. Another and still more important consideration, as to the question whether 5 or 6 atoms, is the equal division of the red oxide by the operation of cold acetic acid; it reduces the 1 oxygen and 6 yellow oxide to 1 and 3 atoms; whereas if we adopt the other, we must conclude it reduces the 1 and 5 to 1 and 2½, a position that cannot well be reconciled to the atomic theory.
According to this conclusion then the red oxide of lead or minium of commerce is constituted of 1 atom of oxygen holding 6 atoms of yellow oxide together; or it is composed of 100 lead and 9.07 oxygen. When itis digested in cold acetic acid the residuum constitutes another oxide consisting of 1 atom of oxygen and 3 of yellow oxide, or 100 lead and 10.4 oxygen, possessing the same colour as the former, but distinguishable by its not being acted on by cold acetic acid, and by its containing twice as much brown oxide and extra oxygen as minium. No doubt the other intermediate oxides of 1 to 4 and 1 to 5 exist, and are all alike red; but have not perhaps any remarkable distinctions besides their containing different proportions of oxygen and brown oxide. Whether an oxide consisting of 1 oxygen and 2 yellow oxide exists, I have not discovered; but that 1 oxygen and 1 yellow oxide are found united, appears below.
III.Deutoxide.This is the flea-brown oxide mentioned above. It may also be obtained by treating solutions of salts containing the yellow oxide by oxymuriate of lime, in which case the oxide is precipitated, leaving the acid in the liquor, a proof that it is insoluble in acids. Its more remarkable properties are: 1st. like the red oxide, when heated to a low red, or treated with sulphuric acid, it yields oxygenous gas, and more copiously; it is thus reduced to the yellow oxide: 2d. with muriatic acid it yields oxymuriatic acid in greatplenty and muriate of lead: 3d. it detonates when rubbed with sulphur in a mortar.
The quantity of oxygen in the brown oxide is stated by Thomson at 25 oxygen to 100 lead, by Berzelius at 15.6 to 100. This last is very nearly right by my experience, and being just double of the oxygen in the protoxide, it warrants us in denominating it the deutoxide. Berzelius finds 100 of the brown oxide lose 6.5 by a red heat so as to reduce it to the yellow; Dr. Thomson finds the loss 9 grains. This difference is easily accounted for; it loses, I find, from 7 to 10 grains per cent. according to the previous degree of dryness; when exposed to a moist atmosphere it attracts humidity; when dried in a temperature of 200° and exposed to red heat immediately after, it does not lose more than 6.5 or 7 per cent. This is corroborated too by the oxygen expelled by sulphuric acid. From 100 grains of brown oxide and sulphuric acid in a gas bottle, I obtained by the heat of a lamp 8.3 oz. of oxygenous gas = 5.3 grains; about 120 grains of grey sulphate of lead were left in the bottle. The oxygen is rather less than was expected; but it must be remembered that 100 grains of brown oxide,obtained in the ordinary way, have the insoluble dross of 500 red oxide in them, which must have some influence in diminishing the production of oxygen.
Though the above might be deemed sufficient to demonstrate the proportion of oxygen in the brown oxide, I was desirous to corroborate the results by oxymuriate of lime. I found repeatedly that 100 grain measures of acetate of lead (1.142) = 13.8 yellow oxide, required 400 measures of oxymuriate of lime = 1 oxygen, to precipitate the whole of the oxide in a brown state. Now if 13.8 ∶ 1 ∷ 97 ∶ 7. Again, into 240 measures of test green sulphate of iron (1.156) = 19 oxide, were put 40 grains of brown oxide of lead, together with a sufficient quantity of muriatic acid to saturate the lead, and discharge the oxygen; after due agitation sulphate of lead was precipitated, and the whole of the oxide of iron was found, when precipitated, to be yellow. But 19 grains oxide of iron require 2+ of oxygen to become yellow; hence the 40 grains brown oxide of lead must have furnished 2+ grains of oxygen to form oxymuriatic acid, which transferred it to the oxide of iron. If 40 ∶ 2+ ∷ 100 ∶ 5+ oxygen, for the excess or second dose of oxygen in 100brown oxide, such as is obtained by nitric acid along with its impurities; which agrees with the results obtained by the other methods.
When zinc is exposed to a strong heat it burns with a brilliant white flame, and a white powder sublimes, which is the oxide of the metal. When dilute sulphuric acid is poured on granulated zinc, hydrogen gas is produced in great abundance and purity; the metal is oxidized at the expence of the water and dissolved in the acid, the oxide may be precipitated by an alkali; it is white both when precipitated and dried, and when heated does not differ from that obtained by combustion. By a violent heat it runs into glass.
The quantity of oxygen in zinc oxide is, I think, best estimated by the hydrogen gas produced during the solution; it may also be obtained by direct combustion, or by solution in nitric acid and calcination. Dr. Thomson determines the oxygen by comparison of the weights of real sulphuric acid and metallic zinc in a solution of sulphate of zinc, along with the consideration that the proportion of sulphuric acid and oxygen in the metallic sulphates is known; Mr. Cavendish obtained 356oz. measures of hydrogen from 1 oz. of zinc by solution. I dissolved 49 grains of zinc in dilute sulphuric acid and obtained hydrogen, after the rate of 363 grain measures for 1 grain of zinc = 182 measures of oxygen = .24 grain of oxygen.
The following are the principal authorities for the quantity of oxygen in zinc oxide, in the order of time.
Now if 24 oxy. ∶ 100 zinc ∷ 7 oxy. ∶ 29 zinc, nearly, which is therefore the weight of an atom of this metal, on the supposition that the oxide is 1 oxygen and 1 metal; and the atom of oxide = 36.
I formerly estimated the atom of zinc at 56 (Vol. 1, page 260). This was occasioned by taking the above as thedeutoxideinstead of theprotoxide. By violently heating the oxide of zinc in a close vessel, Desorme and Clement reduced the oxygen nearly onehalf, so as to afford a presumption that an oxide with half the oxygen of the common one subsisted. Since that time some observations of Berzelius seem to shew that a suboxide of zinc exists. It does not appear however, that such oxide is ever found in combination with acids; and, granting the accuracy of the observations, it is rather to be presumed to be the semi-oxide, or 1 atom of oxygen and 2 of metal, than the protoxide. No higher oxidation of zinc than the above has yet been obtained, and probably does not exist.