_Deutosulphuret of iron._ This is a natural production frequently met with, and in various forms; it is called pyrites, or iron pyrites; it is a yellowish mineral and often appears when broken, of a radiated texture, but sometimes it is crystallized in cubes or dodecahedrons. Acids have little effect upon it, except the nitric, which when diluted attacks both the sulphur and iron; much nitrous gas is produced, the iron is dissolved, and the sulphur chiefly converted into sulphuric acid. This sulphuret consists, according to Proust, of 100 iron, and 90 sulphur, and with this Bucholz recently agrees (Nichols. 27--356); but Hatchett makes it 100 iron, and 112 sulphur. From an experiment of my own on the radiated pyrites, I found nearly equal parts of iron and sulphur. One atom of iron (25,) and two of sulphur (28,) would give 100 to 112; but if the atom of sulphur be only 13, it gives 100 iron to 104 sulphur. Mr. Hatchett unfortunately calculating the proportions of the ingredients _in_ 100 sulphuret, instead of _on_ 100 iron, did not notice that the sulphur in the common pyrites is just double of that in the magnetic pyrites. _Quinsulphuret of iron._ This combination consisting of 5 atoms of sulphur with 1 of iron, is formed by mixing a solution of green sulphate of iron with quadrisulphuret of lime in due proportion. I found 50 measures sulphate 1.168 saturate 310 of 1.05 sulphuret diluted so as to become 6 oz.; this yielded 14 grs. dried sulphuret of iron = 3.6 iron, known to be in the sulphate, and 10.4 sulphur; the liquid contained 2+ sulphur combined with the lime and oxygen of the oxide; for it took 2.3 oxygen by means of oxymuriate of lime to convert the sulphur into sulphuric acid together with 1+ from the oxide, making 3+ oxygen, which unites to 2+ sulphur to constitute 5+ sulphuric acid; and this quantity of acid was found to exist by muriate of barytes together with five more brought in by the sulphate of iron. This sulphuret is a yellowish brown powder; it readily exhales sulphur by heat and is reduced to the protosulphuret; but in the open air it burns with a blue flame and leaves the protosulphuret partially, as I apprehend, oxidized. The theory of the formation of quinsulphuret seems to be this: 3 atoms of quadrisulphuret of lime are requisite to saturate 2 of sulphate of iron; the 2 atoms of sulphuric acid seize 2 of lime, three fourths of the sulphur unite to the iron, and one fourth to its oxygen, forming 2 atoms of oxide of sulphur, which attack the 3d atom of sulphuret and decompose it, giving its sulphur to the iron, and neutralizing the lime (for the liquid is found neutral). In this way 10 atoms of sulphur are united to 2 of iron, and 2 of sulphur to 2 of oxygen, with one of lime, which last compound remains in solution, and the oxide of sulphur may be converted into sulphuric acid immediately by the application of oxymuriate of lime.