Part 2

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 the platina. 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 = 73.3 platina, 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; and if 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 and running 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 its solution 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.)

3. _Oxide of Silver._

When silver wire is exploded by electricity in oxygen gas, a black powder is produced, which is the oxide of silver. If silver be dissolved 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.

silver oxygen Wenzel 100 + 8.5 Proust + 9.5 Bucholz and Rose + 9.5[2] Gay Lussac + 7.6[3] Berzelius + 7.925

[Footnote 2: 7.9 when duly corrected. Annal. de Chimie, 78--114.]

[Footnote 3: Memoirs d’Arcueil 2--168.]

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.

4. _Oxides of Mercury._

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, a yellowish 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 called _calomel_, an insoluble salt; with the deutoxide it forms deutomuriate of mercury, commonly called _corrosive 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 the _black_ oxide in solution; it was however entirely the _red_, 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 the _nitrous gas_ in 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.

Mercury. Oxygen. +------------------+ black. red. Bergman[4] 100 + 4 + -- Lavoisier[5] -- + -- + 7.75 to 8 Chenevix[6] -- + 12 + 18.5 Taboada[7] -- + 5.2 + 11 Fourcroy & Thenard[8] -- + 4.16 + 8.21 Sefstrom[9] -- + 3.99 + 7.99 My results give -- + 4.2 + 8.4

[Footnote 4: Kirwan’s Mineralogy.]

[Footnote 5: Annals of Philosophy, Vol. 3, p. 333.]

[Footnote 6: Philos. Trans. 1802.]

[Footnote 7: Jour. de Physique. 1805.]

[Footnote 8: Mem. d’Arcueil, Vol. 2. p. 168. 1809.]

[Footnote 9: Annals of Philosophy, Vol. 2. p. 48.]

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 be denoted 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.

5. _Oxide of Palladium._

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 oxymuriatic acid = .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.

6, 7, _and_ 8. _Oxides of Rhodium, Iridium, and Osmium._

Nothing certain has yet been determined respecting the oxygenation of these very rare metals.

9. _Oxides of Copper._

There are two oxides of copper according to the results of Proust, Chenevix, Berzelius and others, the proportions of which are given nearly the same by all, and so as to leave no reasonable doubt concerning their accuracy.

1. _Protoxide._ This oxide is _orange_, 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 is _black_; it contains 25 oxygen on 100 copper: the _black_ oxide 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 the solution, 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.

10. _Oxides of Iron._

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

Cavendish (1766) 155 cubic inches. Priestley, from 147 to 162 Lavoisier 163 Vandermonde, Berthollet, } max. 176 and Monge } Vauquelin 160 to 179 Dr. Thomson 163 My own Experiments give 160 ---- Mean 164 = 82 oxygen = 27.9 grains.

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 is _yellow_ at 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 converted into 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. (See VOL. 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.