Part 4
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 great plenty 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 100 brown oxide, such as is obtained by nitric acid along with its impurities; which agrees with the results obtained by the other methods.
14. _Oxide of zinc._
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 356 oz. 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.
Zinc. Oxygen. 1766. Cavendish 100 + 23.3 1785. Lavoisier -- + 19.6 1790-1800. Wenzel and Proust -- + 25 1801. Desorme and Clement -- + 21.7 Davy -- + 21.95 Berzelius -- + 24.4 Gay Lussac -- + 24.4 Thomson -- + 24.42 My own -- + 24
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 the _deutoxide_ instead of the _protoxide_. By violently heating the oxide of zinc in a close vessel, Desorme and Clement reduced the oxygen nearly one half, 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.
15. _Oxides of potassium._
Since writing the articles “potassium and sodium,” in the former volume, a very important essay relating chiefly to these subjects has been written by Gay Lussac and Thenard (a copy of which they were so good as to send me), entitled “Recherches Physico-chimiques, &c.” in 2 VOL.--Many of the most interesting experiments of Davy have been repeated on a larger scale, and a great number of original ones added; these ingenious authors endeavour to sum up the evidences for and against the two hypotheses concerning potassium and sodium, namely, as to their being metals or hydrurets, and upon the whole incline to the former, allowing however, that the facts afford great plausibility to both. One thing they seem to have discovered and established, that the new bodies or metals admit of various degrees of oxidation, and of course these products have a claim to be classed amongst oxides in general though the nature of their bases may still be an object of dispute.
They find three oxides of potassium; the lowest degree is obtained by exposing potassium to atmospheric air in a small bottle, with a common cork; a gradual oxidation takes place; a blueish grey brittle product is obtained; there does not appear however, to be any proper limit to this oxidation besides that which they admit as characterizing the second degree or potash, which degree of oxidation may always be immediately obtained by placing potassium in contact with water. This I think should be called the protoxide and considered as 1 atom of potassium, and 1 of oxygen; before this point it is potassium and potash mixed or perhaps combined.
Besides these there is another obtained by burning potassium in oxygen gas at an elevated temperature; this oxide is yellow, fusible by heat, and crystallizes in lamina on cooling; it contains three times as much oxygen as potash; put into water it is suddenly decomposed, giving out ⅔ of the oxygen in gas and becoming potash. Very probably an oxide containing twice as much oxygen as potash might be formed with some mark of discrimination, by uniting 18 parts potassium with 56 of yellow oxide, but this has not yet been done.
According to these conclusions the weights of the oxides of potassium may be stated as under.--Potassium 35, protoxide or potash 42, deutoxide (supposed to exist) 49, and the yellow or tritoxide 56. Hence we have
Potassium. Oxygen. Protoxide (potash) 100 + 20 } Gay Lussac & Thenard 19 } Davy Deutoxide 100 + 40 (unknown) Tritoxide 100 + 60 Gay Lussac & Thenard
One feels unwilling to admit of a _tritoxide_, (and that perhaps the only one existing,) when the deutoxide is unknown, were it not upon good authority. The obscurity on this subject may be removed by future experiments.
It may be proper to add that Gay Lussac and Thenard concur with Davy in assigning a much greater saturating power to potassium and sodium than to the fused hydrates of potash and soda of equal weights. From the table, Recherches, Tom. 2, p. 214, it may be deduced that 35 potassium require as much sulphuric acid to saturate them as 50 or more of the hydrate of potash; and that 21 sodium are equivalent to 36 or 37 hydrate of sodium. If these results are accurate, the weights of potassium and sodium, considered as hydrurets, cannot be as we have deduced them at pages 486 and 503, VOL. 1, namely, 43 and 29 respectively, but 35 and 21, as at page 262.
16. _Oxides of sodium._
Gay Lussac and Thenard find a suboxide of sodium in the same way as that of potassium, and it is probably a compound of soda and sodium: the remarkable oxidation which produces soda is, I should imagine, the protoxide or one atom to one, as obtained by placing sodium in contact with water. A higher oxide is obtained as with potassium, by burning sodium in oxygen gas with a vivid heat. It resembles the yellow oxide of potassium in its appearance and properties. The degree of oxidation varies in the different experiments from 1¼ to 1¾ times the oxygen of soda. It is probably a combination of the protoxide and deutoxide. Hence the oxides of sodium may be as under; reckoning the atom of sodium 21, and soda 28.
Sodium. Oxygen. Protoxide (Soda) 100 + 33⅓ Intermediate oxide 100 + 50
17. _Oxide of bismuth._
Only one oxide of bismuth is known, and the proportion of its parts has been gradually approximated by Bergman, Lavoisier, Klaproth, Proust, and others. Berzelius mentions a purple oxide obtained by exposing bismuth to the action of the atmosphere; but as no experiments have been made upon it, we cannot adopt it at present. According to Klaproth and Proust, 100 bismuth unite with 12 oxygen; but by the more recent experiments of Mr. J. Davy and Lagerhjelm 100 bismuth take 11.1 or 11.3 oxygen. If we adopt this last, which is doubtless near the truth; we shall have 11.3 ∶ 100 ∷ 7 ∶ 62 for the weight of the atom of bismuth, on the supposition that the compound is the protoxide or 1 atom of metal to 1 of oxygen. My former weight of bismuth was 68 (page 263), which is clearly too high.
Bismuth is best oxidized by nitric acid. Part of the oxide combines with the acid and part precipitates in the state of a white powder; if the whole be gradually heated, the acid is driven off, and at a low red the oxide remains pure; it is fused into glass and of a red or yellow colour, according to the heat employed. Bismuth may also be oxidized by heat in open vessels; yellow fumes arise which may be condensed and are found to be the oxide.
18. _Oxides of antimony._
Considerable difference of opinions exists with regard to the oxides of antimony. Proust finds two oxides which he determines to consist, the first, of 100 metal + 22 or 23 oxygen; the second of 100 metal + 30 oxygen. Thenard finds 6 oxides: J. Davy two oxides, namely, 100 metal + 17.7 oxygen, and 100 + 30 oxygen. Berzelius infers from his experiments that there are 4 oxides of antimony, the first containing 4.65 oxygen, the second 18.6, the third 27.9, and the fourth 37.2 of oxygen on 100 metal. He admits however that the oxide obtained by boiling nitric acid on antimony and expelling the superfluous acid by a low red heat, consists of 100 metal + 29 to 31 oxygen, as determined by Proust and others. This is certainly the most definite of the oxides, next to that which is obtained from the solution of antimony in muriatic acid. This last may be had by pouring water into a solution of muriate of antimony; a white powder precipitates, which is the oxide with a little muriatic acid; the acid may be abstracted by boiling the precipitate in a solution of carbonate of potash. This oxide is a grey powder, and fusible at a low red heat. It enters exclusively into various well known compounds, as the _golden sulphur of antimony_, _antimoniated tartrate of potash_, &c. Its constitution, according to Proust, is 100 metal + 23 oxygen; but J. Davy finds only 17.7 oxygen, and Berzelius 18.6. As this oxide possesses the most distinct features, and besides is the most important, it is desirable its constitution should be ascertained without doubt. From several experiments I made on the precipitation of antimony by zinc, I conclude the oxide contains about 18 oxygen on 100 metal. I took the common muriate of antimony with excess of acid, and immersed a rod of zinc into it, covering the whole with a graduated bell glass. Hydrogen gas was produced by the excess of acid, and its quantity was ascertained; the antimony was in due time precipitated, and when the operation ceased, the loss of zinc and the weight of antimony were found. For instance, to 50 measures of 1.69 mur. ant. 60 water were added, no precipitation was observed; a zinc rod was put in and the whole covered by a bell glass, over water; in a few hours the operation had ceased, and there appeared 3480 grain measures of hydrogen gas generated; the dried antimony weighed 25½ grains, and the zinc had lost 29 grains. Now 3480 hydrogen require 1740 of oxygen = 2.3 grains in weight. But 29 zinc require 7 oxygen; therefore the zinc must have got 4.7 oxygen from the antimony; that is, 25.5 antimony were found united to 4.7 oxygen; this gives 100 antimony + 18.4 oxygen. I conclude then that the error is with Proust; and this appears to be confirmed by the consideration that Proust himself obtains only 86 oxide of antimony from 100 sulphuret, which he allows to contain 74 antimony; now if 74 ∶ 12 ∷ 100 ∶ 17 nearly. I am therefore inclined to adopt 18 for the oxygen which combines with 100 antimony to form the grey oxide. Whether this is the protoxide or deutoxide may be disputed; and the facts known concerning the other oxide or oxides will scarcely determine the case: but the proportions of the muriate and sulphuret of antimony accord much better with the former supposition. Now if 18 ∶ 100 ∷ 7 ∶ 39, for the weight of the atom of antimony; I prefer the weight 40, deduced from the sulphuret, as announced in VOL. 1, page 264.
The oxide which contains 30 on 100 must be 2 atoms of the deutoxide and 1 of the protoxide united. What Berzelius calls the white oxide or antimonious acid, may be 1 atom of each oxide united, containing 27 oxygen on the 100. The oxide supposed to contain 36 or 37 oxygen on 100, and which must be considered as the deutoxide, has not been proved to exist separately. My efforts to procure it have failed as well as those before mine: by treating muriate of antimony with oxymuriate of lime I have obtained oxides of 30 on the 100, but never much higher. Whenever a greater proportion of oxymuriate of lime is added, the smell of the gas becomes permanent.
Antimony exposed to a red heat in a current of common air or oxygenous gas takes fire, and white fumes arise formerly called _flowers of antimony_; this oxide contains 27 or 30 oxygen on 100 metal.
Antimony thrown into red hot nitre is oxidized rapidly; the remaining powder, washed in water, is found to be a compound of oxide of antimony and potash. Berzelius calls the oxide the antimonic acid, and the salt the _antimoniate of potash_. It consists, according to his experience, of 100 acid and 26.5 potash. A similar salt formed between the antimonious acid and potash is constituted of 100 acid and 30.5 potash.
19. _Oxide of tellurium._
We are chiefly indebted to Berzelius for the proportions in which tellurium combines. He finds 100 tellurium unite to 24.8 oxygen. Also that 201.5 tellurate of lead gave 157 sulphate of lead. This last contains 116 oxide of lead, which must therefore have combined with 85.5 of the oxide of tellurium. Hence 97 oxide of lead would combine with 71.5 oxide of tellurium = 57½ tellurium + 14 oxygen. Whether this oxide of tellurium is the protoxide or deutoxide, is somewhat uncertain. The atom of tellurium will weigh 57½ in the latter case, but only 28 or 29 in the former. The analogy of the oxide to acids favours the notion of a deutoxide; but the facility with which the tellurium is volatilized by hydrogen is in favour of the lighter atom. The oxide is a white powder; it is produced by dissolving the metal in nitro-muriatic acid and precipitating by an alkali.
20. _Oxides of arsenic._
There are two distinct combinations of arsenic and oxygen; the one has been long known as an article of commerce under the name of arsenic. It is a white, brittle, glassy substance, obtained during the extraction of certain metals from their ores. Its specific gravity is about 3.7. According to Klaproth boiling water dissolves from 7 to 8 per cent. of the oxide of arsenic; but on cooling it retains only about 3 per cent.; and this I find is gradually deposited on the sides of the vessel till it is reduced to 2 per cent. or less in cold weather, and by some months standing. Water of 60° or under dissolves no more than ¼ per cent. of the oxide. At the temperature of about 400° the oxide sublimes. This oxide combines with the alkalies, earths, and metallic oxides somewhat as the acids do, but does not neutralize them, and in other respects it is destitute of acid properties; as for instance, it does not affect the colour tests. It is extremely poisonous.
The other oxide is obtained by treating either the white oxide or pure metallic arsenic with nitric acid and heat. One hundred grains of white oxide require two or three times their weight of nitric acid, of 1.3, to oxidize them. The new oxide is produced in a liquid form; from which the excess of nitric acid may be driven by a low red heat, and the oxide is obtained pure in the form of a white opake glass, which soon becomes liquid by attracting moisture from the atmosphere. This oxide, discovered by Scheele, has all the properties of acids in general, and is therefore denominated arsenic acid. When just fluid by attracting moisture it has the sp. gravity 1.65 nearly. It is represented as equally poisonous with the white oxide.
The proportions of the elements in these two oxides have been investigated with considerable success. Proust finds the white oxide constituted of 100 metal and 33 or 34 oxygen, and the second of 100 metal with 53 or 54 oxygen: with these results those of Rose and Bucholz nearly agree. Thenard finds 100 + 34.6 for the white oxide, and 100 + 56.25 for the acid: and Thomson 100 + 52.4 for the acid. Berzelius however, infers from his recent experiments that the oxide consists of 100 metal + 43.6 oxygen, and the acid of 100 + 71.3; these last results I have little doubt are incorrect from my own experience.
It appears that when arsenic is oxidized by nitric acid, 100 parts yield from 152 to 156 of acid, dried in a low red heat. The differences may in part be owing to the metal being partly oxidized at the commencement of the operation. On this account I should suppose 55 or 56 to be the proper quantity of oxygen united to 100 metal to form the acid. Proust and Thenard both found that 100 white oxide, when converted into acid by nitric acid, gave 115 or 116. I have found the same. Now if 116 ∶ 100 ∷ 156 ∶ 134; hence the white oxide of arsenic must contain 100 metal to 34 oxygen, if the data be correct; or the metal and oxygen are as 3 to 1 nearly. It is highly improbable that any inferior oxide subsists, as no traces of such have been found, if we disallow a conjecture of Berzelius on the subject. The white oxide of arsenic must then be considered as the _protoxide_, and the atom of arsenic must weigh 21 nearly, and that of the protoxide 28.
It is plain the other is not the _deutoxide_, as it does not contain twice the oxygen of the protoxide; but as the proportion of oxygen in it is to that of the protoxide, as 5 ∶ 3, it may be a compound of 2 atoms of deutoxide, and 1 of protoxide; that is, it may be the _superarseniate of arsenic_, if we consider the deutoxide as the acid, and the protoxide as the base. According to this view, the compound oxide, or _arsenic acid_ of Scheele, is constituted of two atoms of the deutoxide, weighing 70, and 1 atom of the protoxide weighing 28, together making 98, for the weight of an atom of arsenic acid, = 63 arsenic + 35 oxygen: and 100 arsenic take 55.5 oxygen to form the acid, agreeably to the above recited experiments. Singular as this conclusion may appear, the truth of it is put beyond doubt, I think, by the following experiments.
I have repeatedly found that 28 parts of white oxide in solution are sufficient to throw down 24 parts of lime, from lime water, so as to produce 52 parts of arsenite of lime, and leave the water free from both elements. This confirms the notion of the atom of protoxide weighing 28.