Part 6

The green oxide being the most prominent compound next to the chromic acid, being commonly produced from it by any deoxidizing process, being the lowest oxide known, and combining with acids, is on these accounts entitled to the consideration of the protoxide; indeed there does not seem an instance where the protoxide of a metal is unknown, whilst the deutoxide and compound oxides are known. There is however, another oxide observed by Vauquelin and by Berzelius, which is obtained by heating the nitrate, or combination of nitric acid and the green oxide, to dryness and expelling the acid; this oxide is brown, and gives oxymuriatic acid when treated with muriatic acid; on this account it would seem to be intermediate between the green oxide and the chromic acid; it is probably a combination of the two, or the _chromate of chromium_. On the other view however, it must be considered as the deutoxide. What corroborates the notion of the green oxide being 39, is the fact which I have observed, of 46 parts of chromic acid combining with 64 of the green oxide of iron to form 110 of chromate of iron; in this combination the oxide of iron may be said to borrow 1 atom of oxygen from the chromic acid, and the compound may then be considered as the union of the green oxide of chrome, and the red oxide of iron. When this precipitate is subjected to the action of muriatic acid, a green solution is obtained containing the oxide of chrome, and red oxide of iron is precipitated, as Vauquelin has observed. To form the above chromate (or rather subchromate) of iron, let a given portion of neutral chromate of potash be treated with green sulphate of iron, and lime water be added, sufficient to saturate the sulphuric acid, a brown red precipitate is obtained; more sulphate and lime water must be gradually added to the clear liquid till the precipitate become green, when the proportions will be found as above stated. This artificial compound seems a subchromate; whereas the native compound seems to be a chromate. That there is some uncertainty in decomposing a chromate by heat with a view to obtain the green oxide, I have reason to suspect from having decomposed 5⅓ grains of chromate of mercury by a moderate red heat; this compound contained 1.1 chromic acid, and it yielded only .6 of green oxide, whereas it should have been .9 or .8 at least.

Upon the whole I think the evidence is in favour of the opinion that the atom of chrome is 32, the green or protoxide 39, and the deutoxide or chromic acid is 46.

24. _Oxides of uranium._

There appear to be two oxides of uranium from the experiments of Klaproth, Bucholz, and Vauquelin; but the proportions of metal and oxygen have not been very nearly ascertained, from the great scarcity of the minerals containing this metal. (Vid. Bucholz, An. de Chimie, 56--142. Vauquelin, ibid. 68--277; or Nicholson’s Journ. 25--69). The oxides are obtained by precipitation from solutions of the minerals in the nitric or muriatic acid, the foreign substances being first separated.

The protoxide of uranium precipitates dark bottle green by caustic alkalies, and forms crystallizable salts with acids; the other, probably the deutoxide, precipitates orange yellow, and forms uncrystallizable salts with acids; in these respects the oxides bear a near resemblance to those of iron.

Bucholz estimates the yellow oxide at 100 metal + from 25 to 32 oxygen; as it yields oxymuriatic acid when treated with muriatic, it is most likely to be the deutoxide; now if we take 28 for the oxygen combined with 100 metal, the protoxide must consist of 100 metal + 14 oxygen, or of 50 metal + 7 oxygen, and the atom of uranium = 50. From his account of the sulphate and nitrate of uranium the weight of the atom might be inferred to be double of the above or 100. These different conclusions can only be elucidated by future experiments.

25. _Oxides of molybdenum._

The latest and as it should seem most accurate experiments on the oxides of molybdenum were made by Bucholz. (Vid. Nicholson’s Journal, 20, p. 121). There appear to be 3 oxides or combinations of molybdenum and oxygen, namely, the _brown_, the _blue_, and the _white_ or _yellow_. The two last have the character of acids, and none of them seem to form salts with acids, like oxides in general. Bucholz ascertained the above gradation, and that the white oxide or molybdic acid contains ⅓ of its weight of oxygen; (which has since been corroborated by Berzelius); he also found that the blue was best formed by mixing, triturating, and boiling in water 3 parts of brown oxide, and 4 of white, or one of metal, and two of acid; and that it has acid qualities as well as the white. Bucholz also found 3 parts of liquid ammonia of the sp. gr. .97 dissolve 1 of molybdic acid; now 3 parts of ammonia = .186 real (VOL. 1, p. 422); and 1 ∶ .186 ∷ 64 ∶ 12, the quantity of ammonia usually saturated by one atom of acid; and Berzelius found 100 molybdic acid saturate 155 oxide of lead, or 63 acid to 97 oxide. The native sulphuret of molybdenum (the state in which this metal is usually found) was analyzed by Bucholz and found to consist of 60 metal and 40 sulphur.

The molybdic acid may be obtained by roasting the sulphuret in a crucible and stirring it frequently; the sulphur in great part escapes in the form of sulphurous acid and the metal becomes oxidated: carbonate of soda in solution may be added to the residuum as long as any effervescence is observed; molybdate of soda remains in solution and the acid may be precipitated by nitric acid. The brown oxide is best obtained by heating molybdate of ammonia to red; the ammonia and part of the oxygen are expelled, and the brown oxide remains.

There are two views with which the preceding results may be reconciled; namely, 1st. supposing the atom of molybdenum to weigh 21; and 2d, by supposing it to weigh 42 or twice that number. In the first case the brown oxide will weigh 24½ (49) being supposed 2 atoms of metal and 1 of oxygen, the blue or protoxide will weigh 28, and the white oxide or molybdic acid will weigh 63, being a compound of the protoxide and deutoxide, molybdena or native sulphuret will then be as usual, the protosulphuret, consisting of 21 metal and 14 sulphur, or 60 metal and 40 sulphur. In the 2d. case the brown or protoxide will weigh 49, the blue or deutoxide 56, and the acid or tritoxide 63. The native sulphuret, molybdena, must in this view be the deutosulphuret, or 42 metal and 28 sulphur.

The former of these views exhibits the oxides somewhat complicated, but agrees well with the sulphuret; the latter shews the oxides in a more regular train, but does not appear so probable from the sulphuret; besides, the notion of a metallic tritoxide is rather singular, especially in a metal that is rarely if ever found in combination with oxygen. Upon the whole I prefer the former view; but it must be considered as problematical only. The atom of 60 (see page 267 VOL. 1) must doubtless be erroneous.

26. _Oxides of tungsten._

From the experiments of D’Elhuiarts, Bucholz[13] and Berzelius[14] it seems very probable that the tungstic acid is composed of about 100 metal + 25 oxygen. It is a _yellow_ powder of the sp. gr. 6.12, and is best obtained from the native tungstate of lime (a scarce mineral). One part tungstate of lime and four of carbonate of potash are fused together, dissolved in water, and then the tungstic acid may be precipitated by nitric acid. There is an inferior oxide that is black or dark brown; Berzelius reduced the yellow oxide to a flea-brown colour, by sending a current of hydrogen gas through it in a glass tube heated red hot. 100 parts of this oxide burnt be 107 yellow oxide. Hence 100 metal must combine with about 16½ or 17 oxygen to form this oxide, which is ⅔ of that in the yellow or tungstic acid.--Upon the whole it does not seem improbable, considering the great sp. gravity of this metal, that it forms three oxides and that the acid or yellow oxide is the 3d. Hence the atom of tungsten must be 84, that of the protoxide 91, the deutoxide 98, and the tritoxide or tungstic acid 105. The native tungstate of lime, if pure, according to this would be 81.4 acid + 18.6 lime, which is not far from Klaproth’s analysis; he having found 18.7 lime in one specimen; nor from that of Berzelius, he having found 80.4 tungstic acid and 19.4 lime in 99.8 tungstate of lime.[15]

[Footnote 13: An. of Philos. 6--198]

[Footnote 14: An. of Philos. 3-244]

[Footnote 15: An. of Philos. 8--237]

There is another view however, which would accord with the experiments and perhaps will be found preferable in other respects; that is, to suppose the tungstic acid to be composed of 1 atom deutoxide and 1 atom protoxide united; in this case the atom of tungsten = 42, that of the protoxide = 49, that of the deutoxide = 56, and the tungstic acid = 105 as before.

27. _Oxides of titanium._

Nothing certain is known respecting the oxides of titanium. An observation of Richter, quoted by Berzelius (An. of Philos. 3--251), if it could be relied upon, furnishes an important fact, namely, that a solution of muriate of titanium containing 84.4 oxide, gave 150 muriate of silver. Now 150 muriate of silver contain 28 acid; hence 28 acid must have combined with 84.4 oxide; but if 28 ∶ 84.4 ∷ 22 ∶ 66 nearly for the weight of an atom of the oxide. This would indicate 59 for an atom of the metal.

28. _Oxides of columbium._

The white oxide or acid of columbium is found in combination with the oxides of iron and manganese in proportion nearly as 4 of the acid to 1 of the aggregate oxides. The two minerals, columbite and tantalite, though yielding these substances nearly in the same proportions, are found to differ remarkably in specific gravity, the former being about 5.9 and the latter about 7.9. Dr. Wollaston concludes however, from the agreement of the white oxides extracted, that they must be the same. The white oxide of columbium is insoluble in the mineral acids; it unites with potash by fusion, and may be precipitated by most acids. Some of the vegetable acids, the oxalic, the tartaric, and the citric dissolve the white oxide. When the alkaline solution of columbium previously neutralized by an acid is treated with infusion of galls, an orange precipitate is produced which is characteristic of columbium. Nothing certain has been determined respecting the proportions of metal and oxygen; but from the great proportion of the columbic acid found with the oxides of iron and manganese, together with the great sp. gravity of the compound, one may pretty clearly infer the great weight of the atom of columbium. Supposing the white oxide or acid to consist of 1 atom metal + 3 oxygen and that the columbite is formed by 1 atom of acid to 1 of oxide, we should have 128 acid + 32 oxide. This would give 107 for the weight of an atom of metal, and 128 for that of the tritoxide or columbic acid; but it is unnecessary to dwell upon such conjectures.

In a recent memoir of Messrs. Gahn, Berzelius, and Eggertz (An. de Chimie, Octo. 1816), it is maintained as probable that there is only one oxide of columbium or tantalum, and that 100 metal take 5.485 oxygen, or 121 metal take 7 oxygen. If this be correct, the atom of columbium must be 121 and the protoxide 128.

(See also An. de Chimie, 43--271; Philos. Trans. 1802; Nichols. Journ. 2--129; ibid. 3--251; ibid. 25--23).

29. _Oxides of cerium._

The mineral cerite is of the sp. gr. 4.53, and constituted of 50 or 60 per cent. of oxide of cerium, with silex, lime, and iron. This mineral being calcined and dissolved in nitro-muriatic acid, the solution is to be neutralized by caustic potash, and then treated with tartrate of potash. The precipitate, well washed and afterwards calcined, is pure oxide of cerium. This oxide, which is white, when calcined in the open air becomes red and acquires more oxygen. These oxides, particularly the white, are soluble in most acids; the red oxide with muriatic acid gives oxymuriatic acid.

The experiments hitherto made on this subject scarcely enable us to decide respecting the proportions of metal and oxygen, nor the relative weights of these oxides.

Both Vauquelin[16] and Hisinger[17] agree that the protocarbonate of cerium, when exposed to a red heat, yields 57 or 58 oxide, which the former says is the red oxide, being changed by the calcination. Hisinger finds the percarbonate to consist of 36.2 acid and 63.8 oxide: also that the muriate of cerium consists of 100 acid and 197.5 oxide; but Vauquelin remarks that the sulphate, nitrate, and muriate of cerium are always more or less acid, however dried; and he found the protoxalate of cerium to yield 45.6 red oxide by calcination, on a mean of 3 experiments not much differing from each other. Supposing all these facts accurate, they may be reconciled by a few suppositions by no means improbable. Let the atom of cerium be 22, the protoxide 29, and the red oxide 32½ (that is, 1 oxy. + 2 protox. = 65); and let the protocarbonate be 1 atom of acid, 1 of oxide, and 1 of water; the percarbonate, 1 acid 1 oxide; the oxalate, 1 acid (40) and 1 oxide; and the muriate, saturated with base, 3 oxide and 2 acid. Then it will be found that,

[Footnote 16: An. de Chimie, 54--28]

[Footnote 17: An. of Philos.--4--356]

The decomposed protocarbonate will yield 57.5 red oxide; The decomposed percarbonate will yield, 36.7 acid, 63.3 oxide; The decomposed oxalate will yield 47 red oxide; and The muriate will yield 100 acid (22), and 197.7 oxide.

All of which agree very nearly with the results above obtained.

Hence it appears to me very probable that the several atoms of the metal and the oxides are as stated above; and that,

100 cerium + 31.8 oxygen = 131.8 protoxide, white. ---------- + 47.7 ------ = 147.7 intermediate, red.

Hisinsger, from some of the same data united to other hypothetical facts than those assumed above, deduces the two oxides very different; viz. 100 metal + 17.4 oxygen for the protoxide, and 100 + 26.1 for the peroxide.

SECTION 14.

EARTHY, ALKALINE AND METALLIC SULPHURETS.

The sulphurets exhibit a very important class of combinations of two elements. Many of the metals are found chiefly in the state of native sulphurets, and are extracted by particular processes. Artificial combinations of sulphur and the metals, and of sulphur and the earths and alkalies are commonly practised, and are found useful in chemical investigations. The alkaline and earthy sulphurets will scarcely be allowed perhaps to be combinations of _two elements_ only; but their analogy with the other compounds is such as to induce us to treat of them under this head, especially as they are agents occasionally in the formation of metallic sulphurets, and these cannot be so well understood without some knowledge of the other. For like reasons the compounds of three elements, sulphur, metal, and oxygen, called sulphuretted oxides, and sulphuretted sulphites, and those of four elements, sulphur, metal, oxygen and hydrogen, called hydrosulphurets, may be considered at the same time, having an intimate relation with the sulphurets strictly so called, or the compounds formed with sulphur and the undecompounded bodies.

Sulphur may be combined with the earths, alkalies and metals, by heat, of various degrees according to the nature of the subjects. The union is attended in many cases with a glowing ignition, indicating the evolution of heat. The metallic oxides and sulphur when heated together commonly produce a sulphuret of the metal, whilst the oxygen escapes with part of the redundant sulphur in the form of sulphurous acid, and the rest of the sulphur sublimes.

In the humid way sulphur may be combined with earths, alkalies, and metals, by means of sulphuretted hydrogen, hydrosulphurets (that is, sulphuretted hydrogen united to other alkaline or earthy bases), and hydroguretted sulphurets (a name given to certain earthy and alkaline sulphurets formed mostly by boiling mixtures of the respective bases and sulphur in water.) The sulphuretted hydrogen may be used in this state of gas or combined with water; the hydrosulphurets and hydroguretted sulphurets are best applied in their watery solutions. The metals are to be used in this case in the state of salts, that is, oxides united to acids, and in solution; or their oxides may in some instances be precipitated previously to the addition of the sulphur compound; the alkalies and earths are sometimes directly sulphurized in the state of hydrates, and at other times by double affinity, in the state of salts or combined with acids. The phenomena in the case of sulphurets formed in the humid way, are various and often complicated, and the true results are not always to be obtained without considerable difficulty and uncertainty.

1. _Sulphurets of lime._

When pounded lime and sulphur are mixed together, and heated in a crucible scarcely any union takes place; the sulphur sublimes or burns away and leaves the lime unaltered. If for lime we substitute carbonate of lime, it also remains unaltered. But if hydrate of lime and sulphur are heated together in equal weights, the hydrate is decomposed, and the lime unites to a portion of the sulphur, whilst the excess of sulphur sublimes or burns and escapes at a low red heat. The residue, about 60 per cent. of the original weight, is a yellowish white powder, composed of sulphur and lime. If this be again treated with sulphur and heated, it undergoes no material change; the last sulphur entirely escaping, leaves the sulphuret unaltered, and hence shews that it must be a true chemical compound.

Now if 32 parts hydrate of lime, which consist of 24 lime and 8 water, be mixed with 32 sulphur and heated as above, they will yield 38 parts sulphuret, which must be composed of 24 lime and 14 sulphur, or sulphur and water; but it appears from the analysis hereafter to be given, that the whole of this last part is sulphur; therefore the compound is formed of 1 atom of lime, and 1 of sulphur, and is the _protosulphuret_ of lime.

When 32 parts of common hydrate of lime and 56 sulphur, are boiled together in 1000 parts water for half an hour, or more, occasionally adding water to supply the waste, a fine yellow liquid is obtained, with a few grains of residuum containing both lime and sulphur nearly in the original proportion with a few grains of alumine. This liquid of course contains in solution, a combination of 1 atom of lime, or perhaps hydrate of lime, and 4 atoms of sulphur; and may therefore be called a _quadrisulphuret_ of lime. If more sulphur or lime than the above proportion be used, the surplus will remain in the residuum uncombined, shewing that by this process no other than a quadrisulphuret can be formed. A similar solution may be obtained in cold water by frequent agitation; but it is much slower in producing the effect. The strength of liquid quadrisulphuret depends upon the relative quantity of the ingredients. I have boiled it down till the water was only 5 times the other materials, which appears to be its maximum strength in the common temperature; its specific gravity was 1.146; but in general I have used it of less than 1.07 density. It may be proper to remark here that I find the decimals multiplied by 4 express very nearly the number of grains of lime in 1000 grains measures of the solution, and multiplied by 9 those of the sulphur; on this account a solution of the sp. gravity 1.06 facilitates the calculations, as 100 measures of it contain 2.4 grains of lime, and 5.4 or 5.6 of sulphur nearly.

It is rather surprising that no bisulphuret nor trisulphuret of lime should be formed this way. One would suppose that the sulphuret of lime in its progressive changes would have passed through the forms of bisulphuret, &c. till it had obtained its maximum of sulphur when that was in excess; but, as has been observed, the quadrisulphuret is the only one formed, whatever may be the proportions of the ingredients. I imagine the reason to be, that the sulphur has to decompose the hydrate of lime, and that no fewer than 4 atoms of sulphur are adequate to that effect; it is known that water adheres so strongly to lime as to require a red heat to separate it. When therefore we mix lime water with quadrisulphuret of lime, it must be considered as a mere mixture of the two, and that the lime does not divide the sulphur equally. Consistently with this reasoning, whenever the lime is in excess in forming quadrisulphuret of lime, we ought to consider the liquid solution as _lime water_ holding quadrisulphuret of lime. This distinction will be of some importance when the solution is weak, because then the lime in the lime water will be considerable, compared with the lime combined with sulphur.

1. _Protosulphuret._ The properties of this compound are;--about 1 grain is soluble in 1000 water; this water, as well as the powder itself, tastes like the white of an egg; salts of lead are thrown down black by the solution; weak nitric and muriatic acids dissolve the lime, and leave the sulphur; 100 parts of test acid require 19 of the powder, and yield 7 of sulphur; indicating the compound to be 12 lime and 7 sulphur. The same conclusion may be obtained by means of a solution of lead; if water containing 1.9 grains of the powder be precipitated by nitrate of lead, it will require 7 grains of the salt = 2.2 acid and 4.8 oxide, or 4.5 lead, and about 5 or 5½ grains of sulphuret of lead will be formed, and the liquid will contain 3.4 grains of neutral nitrate of lime.

2. _Quadrisulphuret._ This combination has been long known, and some of its properties observed; but I have not found in authors any determination of its proportions. It is of a beautiful yellow or orange colour, and 1 grain imparts very sensible colour to 1000 of water; it has a disagreeable bitter taste; when evaporated down, it crystallizes or rather perhaps solidifies into a yellowish mass; but its properties are affected by the process from the acquisition of oxygen. This mass when dried, burns with a blue flame and loses 40 per cent.; the remainder is a white powder, a mixture of sulphite and protosulphuret of lime. Liquid quadrisulphuret exposed to the atmosphere soon becomes covered with a white film which arises from the sulphur displaced by oxygen gas; this film being broken subsides, and another is formed, and so on successively till at length the acquisition of oxygen ceases with the deposition of sulphur, and the liquid remains quite colourless. It is intensely bitter, and contains lime, sulphur and oxygen in proportions to be presently determined. This colourless liquor undergoes a gradual change by being kept for years in a bottle with a common cork; a deposition of some sulphur and sulphate of lime takes place, but whether from a further acquisition of oxygen gas or from some internal chemical action, I have not had an opportunity of observing.