When quadrisulphuret of lime is treated with as much sulphuric acid as is sufficient for the lime, the sulphur is in part precipitated, but it is in union with the sulphate of lime, or at least they are not separable by mechanical means. This compound is sold in the shops under the name of precipitated sulphur. It is about one half sulphate of lime, and the other half sulphur. The nitric and muriatic acids precipitate the sulphur partially from quadrisulphuret, but the sulphur assumes a viscid form and exhales sulphuretted hydrogen, and the proportion of the elements of quadrisulphuret are not easily obtained by any of these acids.
The mutual action of quadrisulphuret of lime, and the metallic salts is curious and interesting; for instance, with nitrate of lead. Let a solution of nitrate of lead, containing 97 oxide, be treated with a solution of quadrisulphuret of lime by degrees, as long as a black precipitate appears, marking the exact point of saturation; this will be found when 36 parts of lime have entered, and 84 of sulphur; the sulphuret of lead will fall, and when dried will weigh 145 parts, and contain 90 lead, and 55 sulphur; that is, 1 atom of lead, and 4 of sulphur, and is consequently a quadrisulphuret of lead. The liquid remains clear and colourless, and contains the nitric acid, lime, oxygen of the lead, and ⅓ of the sulphur; each atom of nitric acid combines with one of lime, which retains one of the 4 atoms of sulphur, forming a sulphuretted nitrate of lime, consisting of 45 acid, 24 lime, and 14 sulphur; the 7 parts of oxygen unite with 7 of sulphur to form sulphurous acid, which require 12 parts of lime to saturate them and 7 of sulphur, forming a sulphuretted sulphite of lime: hence we see that 28 parts of sulphur remain in the liquor, and the rest (56) unite with the lead. If now we add gradually more nitrate of lead, a silvery white precipitate appears, increasing till half the original quantity is added, and then the liquid is saturated. This white precipitate is sulphuretted sulphite of lead; when heated it soon grows black and loses 15 or 20 per cent., being then a protosulphuret of lead. The liquid now contains sulphuretted nitrate and simple nitrate of lime; nitrate of lead has no effect, but nitrate of mercury precipitates a black sulphuret.
Quadrisulphuret of lime saturated with oxygen, as has been observed, contains sulphuretted sulphite of lime in solution, and deposits sulphur: the liquid treated with nitrate of lead, gives as above the white, silvery sulphuretted sulphite of lead as a precipitate, and holds nitrate of lime in solution.
Hydrosulphuret of lime. This compound may be formed by passing sulphuretted hydrogen into lime water; the water assumes a brownish colour, but the point of saturation is not easily found, as the lime water is not neutralized so as to shew by the colour test, and water of itself absorbs above twice its volume of the gas. By means of a neutral solution of nitrate of lead it may be found that 1000 lime water in volume, require about 600 sulphuretted hydrogen, because then a mutual saturation is observed by double affinity; that is, sulphuret of lead and neutral nitrate of lime are formed; but otherwise the liquid remaining is either acid or alkaline. Hydrosulphuret of lime, as well as the other hydrosulphurets, has a peculiar bitter taste. It forms a useful reagent in regard to metals, but is apt to be spoiled by keeping, owing to the acquisition of oxygen.
2. Sulphuret of magnesia.
I have not succeeded in endeavouring to combine sulphur and magnesia in the dry way; but a liquid sulphuret is easily formed by the action of double affinity.
Let a quantity of the liquid quadrisulphuret of lime be treated with a solution of sulphate of magnesia, so that the sulphuric acid may be sufficient for the lime; by digesting in a moderate heat, the sulphate of lime is precipitated, carrying with it one fourth of the sulphur, and a trisulphuret of magnesia remains in solution. I have not observed any remarkable feature of distinction between this sulphuret and that of lime, except as above noticed in the proportions of their compounds.
Hydrosulphuret of magnesia. This compound may be formed by pouring sulphuretted hydrogen water into recently precipitated magnesia; it does not differ much from that of lime. One atom of sulphuretted hydrogen (15), combines with one of magnesia (17), and the compound is soluble in water.
3. Sulphuret of barytes.
Protosulphuret. The protosulphuret of barytes may be procured the same way as that of lime, by heating hydrate of barytes and sulphur till the mixture becomes red. It is very little soluble in water, and accords in other respects with the like compound of lime. It consists of 68 barytes and 14 sulphur, or 100 barytes and 20½ sulphur.