Chapter 76

HYDROGEN SULPHIDE.

Examine ferrous sulphide, natural and artificial.

191. Preparation.

Experiment 108.--Put a gram of ferrous sulphide (FeS) into a t.t. fitted with a d.t., as in Figure 32. Add 10cc. H2O and 5cc. H2SO4. H2S is formed. Write the equation, omitting H2O. What is left in solution?

192. Tests.

Experiment 109.-(1) Take the odor of the escaping gas. (2) Pour into a t.t. 5cc.solution AgNO3, and place the end of the d.t. from a H2S generator into the solution and note the color of the ppt. What is the ppt.? Write the equation. (3) Experiment in the same way with Pb(NO3)2 solution. Write the equation. (4) Let some H2S bubble into a t.t. of clean water. To see whether H2S is soluble in H2O, put a few drops of the water on a silver coin. Ag2S is formed. Describe, and write the equation. Do the same with a copper coin. (5) Put a drop of lead acetate solution, Pb(C2H3O2)2, on a piece of unglazed paper, and hold this before the d.t. from which H2S is escap- ing. PbS is formed. Write the equation. This is the characteristic test of H2S.

193. Combustion of H2S

Experiment 110.--Attach a philosopher's lamp tube to the H2S generator, and, observing the same precautions as with H, light the gas. What two products must be formed? State the reaction. The color of the flame. Compute the molecular weight and the vapor density of H2S. 194. Uses. -Hydrogen sulphide or sulphuretted hydrogen, H2S, is employed chiefly as a reagent in the chemical laboratory. It forms sulphides with many of the metals, as shown in the last experiment. These are precipitated from solution, and may be separated from other metals which are not so precipitated, as was found in the case of HCl and NH4OH. The subjoined experiment will illustrate this. Suppose we wished to separate Pb from Ba, having salts of the two mixed together, as Pb(NO3)2 and Ba(NO3)2.

195. H2S an Analyzer of Metals.

Experiment 111.--Pass Some H2S gas in to 5cc.solution Ba(NO3)2. No ppt. is formed. Do the same with Pb(NO3)2 solution. A ppt. appears. Now mix 5cc.of each of these solutions in a t.t. and pass the gas from a H2S generator into the liquid. What is precipitated, and what is unchanged? When fully saturated with the gas, as indicated by the smell, filter. Which metal is on the filter and which is in the filtrate? Other reagents, as Na2CO3 solution, would precipitate the latter.

196. Occurrence and Properties. -- H2S is an ill-smell- ing, poisonous gas, formed in sewers, rotten eggs, and other decaying albuminous matter. It is formed in the earth, probably from the action of water on sulphides, and issues with water from sulphur springs.

A characteristic property is the formation of metallic sulphides, as above. A skipper one night anchored his newly painted vessel near the Boston gas-house, where the refuse was deposited, with its escaping H2S. In the morning, to his consternation, the craft was found to be black. H2S had come in contact with the lead in the white paint, forming black PbS. This gradually oxidized after reaching the open sea, and the white color reappeared.