For instance, from solutions containing certain metallic salts, sulphuretted hydrogen throws down the metals as sulphides, provided the solution has been previously made slightly acid. Copper, arsenic, tin, and cadmium, are some of the metals thrown down under these conditions.

The salts of iron, nickel, cobalt, and certain others, although they do not yield precipitates under like circumstances, are found to do so if their solutions are made alkaline instead of acid. Again, there are other salts, those of the alkalies and alkaline earths, which, when sulphuretted hydrogen is passed through these solutions, give no precipitates either in acid or alkaline solutions. The chemist, therefore, in the course of an analysis, frequently avails himself of a knowledge of these facts to separate certain metals from each other.

Hydrogen, Persulphide of. Syn. Hydric persulphide, Hydrogen disulphide. To procure this substance, calcium disulphide (CaS2) in solution is poured into hydrochloric acid diluted with twice its bulk of water. The solution being gently warmed, the persulphide

subsides at the bottom as an oily fluid. Hydric persulphide has a great resemblance to hydric peroxide in qualities. It bleaches, and is decomposed, with violence, when brought into contact with the oxides of manganese and silver. It easily decomposes into sulphur and sulphuretted hydrogen.

SULPHU′RIC ACID. H2SO4. Syn. Oil of vitriol, British o. of v., Vitriolic acid†; Acidum sulphuricum (B. P., Ph. L. & E.), Acidum sulphuricum venale (Ph. D.), Acidum vitriolicum†, L. This acid, in a concentrated form, was discovered by Basil Valentine towards the end of the 15th century. At first it was obtained by the distillation of green vitriol, but is now made by the oxidation of sulphurous anhydride, obtained by the combustion either of sulphur or of certain sulphides. In consequence of the growing demand for sulphur in the manufacture of gunpowder, ultramarine, and for the destruction of the vine parasites in the vineyards of France, Italy, and Spain, sulphuric acid is now seldom made by burning sulphur, but, with few exceptions, by roasting iron pyrites, or bisulphide of iron.

The following table will convey an idea of the enormous consumption of this mineral in vitriol making in England alone. The quantities given represent tons.

Date.Pyritesfrom[212]Sum Total.
Norway.Germany.Belgium.Portugal.Spain.Italy.Sundry Places.
18624,9756,8179,86053,29633,717...2,187110,852
18636,73615,40912,059109,18033,213...2,628179,225
186416,08712,7517,069118,48915,529...1,065170,990
186522,22914,7272,121137,78716,393...369193,626
186638,26221,5744,006165,99311,910...1,625244,596
186777,89534,5922,299105,55650,222...2,134272,698
186863,00741,559...75,88347,4587941,019229,720
186963,09113,983...140,80599,648...2,420319,947
187067,46414,914...174,459150,990...3,676411,512
187174,41612,809...120,573242,163...4,581454,542
187271,6655,682...180,329257,429...2,521517,626

[212] “Development of the Chemical Arts during the last Ten Years,” by Dr A. W. Hofman (‘Chemical News,’ vol. xxv, 1879).

Of the other sulphides employed in vitriol making may be mentioned galena, or native sulphide of lead, which, when roasted, is made to give up half its sulphur. The chief consumption of this mineral is in the Harz. Copper pyrites is also used in the Harz, as well as in Swansea and Glasgow. Blende, or native sulphide of zinc, is also occasionally had recourse to.

In addition to the above sulphides, the vitriol maker in England, France, and Germany has lately largely availed himself of a compound known as ‘Laming’s mixture,’ which is an impure oxide of iron that has been used in gas manufacture for the removal from the gas of the sulphur. Laming’s mixture is consequently rich in this last element.