A new system of chemical philosophy, Volume 2, Part 1

by John Dalton

Water impregnated with the gas was found to have like effects as the gas itself. Whence Oberkampf concludes that as long as an excess of gold remains in solution, the phosphuretted hydrogen precipitates the metal only; but when the gas is in excess, the phosphorus leaves the hydrogen and unites with the precipitated gold.

I should rather suppose that the precipitation of the gold may be, in part at least, owing to the free hydrogen which we now know accompanies the phosphuretted hydrogen largely, in the manner in which this gas was formerly procured; however that may be, I find that water, impregnated with the purest phosphuretted hydrogen, has the property of precipitating the black phosphuret of gold from the muriate of that metal, in such manner as to effect complete mutual saturation, leaving nothing in the liquid but the muriatic acid. Let a solution containing a known quantity of gold be gradually dropped into water, containing a known quantity of phosphuretted hydrogen, as long as any black precipitate is formed. The point of saturation will be found when 60 parts by weight of gold have united to 9 of phosphorus, nearly; or when one atom of gold has united to one of phosphorus. Hence it may be concluded that 100 grains of the phosphuret of gold contain 13 or 14 of phosphorus, which agrees very nearly with the results of Mr. Edmund Davy abovementioned.

8. Phosphuret of platina.

M. Pelletier succeeded in combining platina with phosphorus by the same methods as with gold. By projecting phosphorus on grains of platina heated to a strong red, the latter acquired an increase of weight of 18 on the hundred; but this was probably an excess, as some vitreous phosphoric acid was found mixed with the mass.

In the Philos. Magazine, Vol. 40, Mr. E. Davy has related some experiments made with a view to combine platina and phosphorus; he effected it by heating platina and phosphorus together in an exhausted tube; the union commenced below a red heat and was attended with vivid ignition and flame. The compound was of a blueish grey colour and consisted of 82½ platina and 17½ phosphorus according to his estimate. Also by heating the ammonia-muriate of platina with ⅔ of its weight of phosphorus in a retort over mercury, muriatic gas was liberated, and muriate of ammonia and phosphorus were sublimed, but there remained at dull red heat an iron black or dark grey mass at the bottom, of the sp. gr. 5.28. It was estimated to consist of 70 platina and 30 phosphorus; but I doubt whether it could consist of these two elements only.

Phosphuretted hydrogen water scarcely has any effect on muriate of platina. After some time a very light flocculent matter appears, as Dr. Thomson has observed; but this seems to me to be nothing but a slight precipitation of phosphorus alone; I apprehend the gas unites with the platina, but the compound remains in solution somewhat in the same manner as platina and sulphuretted hydrogen. The platina may be precipitated from the clear liquid by muriate of tin, much the same in appearance as if no phosphuretted hydrogen were present.

9. Phosphuret of silver.

When pieces of phosphorus are dropped amongst silver heated to red in a crucible, the two unite and enter into fusion, according to Pelletier; when the metal is saturated with phosphorus the whole continues in a state of tranquil fusion; but being withdrawn from the fire, at the moment of congelation, a quantity of phosphorus becomes suddenly volatile and burns vividly, and the surface of the metal becomes uneven. The metal on being cooled, is found to have gained from 12 to 15 per cent.; and he apprehends that when fluid it contains 10 per cent. more, making in all 25 phosphorus to 100 silver.

The phosphuret of silver is white and crystalline, brittle under the hammer, but capable of being cut with a knife. By a strong heat the phosphorus is dissipated and leaves the silver pure.

Both Raymond and Thomson observe that phosphuretted hydrogen water precipitates silver from its solutions of a black colour. I find that a solution of sulphate of silver containing one grain of the metal, requires water containing 90 grain measures of phosphuretted hydrogen to saturate it; the whole of the silver falls readily and leaves nothing but the acid in the water. Now the weight of 90 measures of this gas is nearly ⅑ of a grain; hence the proportions of metal and phosphorus are as 10 to 1, which shows that they combine atom to atom, or 90 silver to 9⅓ phosphorus. This is somewhat less of phosphorus than is determined above by Pelletier.