_Trisulphuret of silver._ This compound is formed whenever neutral nitrate of silver is dropped into a solution of quadrisulphuret of lime or alkali. Mutual saturation seems to take place when eight atoms of nitrate meet with seven of quadrisulphuret. Trisulphuret of silver is constituted of 90 silver, and 42 sulphur; or of 100 silver, and 46.5 sulphur. Its colour is not so dark as that of the protosulphuret. The residuary liquid contains sulphurous acid, which is easily converted into sulphuric by the addition of a portion of lime; and the quantity of acid may then be determined by muriate of barytes. 16. _Sulphurets of mercury._ Mercury combines readily with sulphur both in the dry and humid way, and that in several proportions, as under: namely, 1. _Protosulphuret of mercury._ This is most conveniently formed by passing sulphuretted hydrogen gas through a solution of the protonitrate of mercury, or by pouring hydrosulphuret of lime, &c. into the same solution. The protosulphuret falls down in the state of a black powder. It consists of 167 mercury, and 14 sulphur; or of 100 mercury, and 8.4 sulphur. The theory of its formation is the same as that of silver. 2. _Deutosulphuret of mercury._ This is formed in the humid way whenever sulphuretted hydrogen or a hydrosulphuret in excess is mixed with the deutonitrate or deutomuriate of mercury (corrosive sublimate); a brown powder is precipitated which is the deutosulphuret. If the sulphuretted hydrogen be only one half what is sufficient to form the deutosulphuret, then we obtain no sulphuret, but instead of it a protonitrate or protomuriate, as was first intimated by Proust; I find however, the atom of sulphur adheres to the atom of salt, and that it is therefore a sulphuretted protonitrate or muriate, whilst 1 atom of oxygen unites with the hydrogen. The brown precipitate does not change to yellow, orange, and red, when left undisturbed for a few days, in my experience; though this is stated to have been observed by Mr. Accum. Notwithstanding the difference in colour, this deutosulphuret must be the same nearly as the cinnabar and vermillion of commerce, if Proust and others are right in their analysis of these articles. The combination of the elements of sulphur and mercury when intended to form cinnabar is made in the dry way by trituration, and a moderate heat: the compound, at first black, is afterwards sublimed by a duly regulated heat and becomes red. This compound must consist of 100 mercury and 17 sulphur nearly.