CHLORINE.

141

Estimation of Hypochlorites.

The hypochlorites are seldom pure, but contain, from the method of theirpreparation, constituents which more or less direCtly bear upon the correctnessof the observation. Hypochlorite of lime contains besides, as we haveseen, chloride of calcium and hydrate of lime. The hypochlorites of potashand soda contain carbonates and chlorides of the respective bases.

Two equivalents of chlorine correspond to 1 equivalent of hypochlorousacid, or (2 equivalents of chlorine being equal to 71 parts of chlorine) to 71-5parts of hypochlorite of lime, 74 - 5 parts of hypochlorite of soda, or go-y partsof hypochlorite of potash.

In order to estimate the value of a hypochlorite of lime, 10 grms. of thesample to be tested should be rubbed down with a small quantity of water, toform a smooth milky fluid: this milk should be poured into a mixing beaker,and the residue remaining in the mortar should be washed with water, and thewash-water added to the contents of the beaker. The milky liquid should thenbe diluted to 500 c.c. 50 c.c. of this solution should then be brought under theburette containing the normal arsenious acid solution, which must be addeduntil the iodide test-paper is no longer tinged blue. Then the solution shouldbe titrated back with the normal iodine solution, until the blue colour isre-established. The number of c.c. of iodine solution employed divided by 10,subtracted from the number of c.c. of normal arsenious acid employed, willgive a difference which, multipled by 0*00355, produces the required weight ingrammes. For example, suppose 50 c.c. = 1 grm. of hypochlorite of lime, torequire 92 c.c. of the normal arsenious acid solution for the titration, and18 c.c. of the iodine solution for the second titration; then g2 — i*8 = go*2 c.c.,and 90*2x0*00355=0*32021 grm. of chlorine, or of hypochlorite of lime con-taining 32*021 per cent of chlorine.

The applications of the salts not described in this section will be foundrecorded during the subsequent pages of the work.