_Trisulphuret of gold._ This compound is obtained whenever quadrisulphuret of lime is gradually dropped into a solution of muriate of gold; it is a black powder, not quite so deep as the former. Care must be taken to saturate the excess of acid previously by lime water, to prevent any uncombined sulphur precipitating. Trisulphuret of gold being heated, burns with a blue flame, and leaves the gold nearly pure; it loses from 10 to 45 per cent. by the process. It is constituted of 1 atom gold and 3 sulphur, or 60 gold and 42 sulphur, nearly; or 100 gold combine with 70 sulphur. From several experiments I am led to conclude that each atom of oxide of gold takes 3 of sulphur, and parts with 1 of oxygen to the remaining sulphur; thus a trisulphuret of gold is formed, and an oxide of sulphur; the liquid, being afterwards treated with oxymuriate of lime, is found to require twice the oxygen of the gold for its saturation, when a corresponding portion of sulphuric acid may be precipitated by muriate of barytes. 14. _Sulphuret of platina._ Sulphur may be combined with platina in several ways, and probably in different proportions; but the combination is not so easily and elegantly effected as with many other metals, and hence some uncertainty still remains on the subject. When a salt of platina is treated with sulphuret or hydrosulphuret of lime, or sulphuretted hydrogen water, the liquid slowly and gradually grows dark brown and finally black; after agitation and standing a few hours, the liquid is semitransparent, and a black flocculent precipitate appears at the bottom. Sometimes after violent agitation, the liquid on standing a few minutes becomes a transparent brown, but soon grows turbid again. In the course of a few days, and by occasional agitation, the liquid finally becomes clear and nearly free from platina, and the precipitate may be collected on a filter and dried. This circumstance of slow and indolent precipitation cannot be prevented by any means I have found, such as saturating the excess of acid, &c. Mr. Edmund Davy, in the 40th VOL. of the Philos. Magazine, has given us the results of his experiments and observations on the sulphurets of platina, containing some useful and original information. He combines platina with sulphur by heating the ammonia-muriate of platina with sulphur; also by heating platina and sulphur in an exhausted tube; and by sending sulphuretted hydrogen gas or water into a solution of muriate of platina; this precipitate he calls hydrosulphuret of platina. He has just noticed the precipitate formed by sulphuret of potash with muriate of platina, but gives no opinion as to the compound obtained this way. He determines three sulphurets, namely, Subsulphuret, 100 platina + 19 sulphur Sulphuret, 100 ---- + 28.2 ---- Supersulphuret, 100 ---- + 38.8 ----