63. HTDEOCIILORIC ACID. 95 



water-bath, ignite tlie residue until it begins to fuse, and 

 weigh it. 



When this precipitate of argentic chloride is produced 

 in the presence of much organic matter, it, together with 

 the ash of the filter, must be fused with 3 or 4 parts of 

 pure sodic carbonate, and the fused mass exhausted with 

 w^ater, the insoluble residue w^ell washed, and the solu- 

 tions and washings re-precipitated with argentic nitrate, 

 and the precipitate treated as directed above for washing 

 and ignition. 



The precipitate contains 24.74" \^ of chlorine. 



b. Volumetric Process. — To prepare the standard solu- 

 tion of argentic nitrate, dissolve 18.75-18.8 grms. of 

 the pure fused salt in 1100 c.c. of distilled water, filter 

 the solution if necessary, and mix all parts of it well 

 together. 



Weigh out accurately four portions of pure sodic chloride 

 of 0.1-0.18 grms. each; the salt should have been pre- 

 viously gently ignited, pulverized while warm, and kept 

 in a well stoppered bottle until wanted for use. 



Dissolve each j)ortion of the salt in 20-30 c.c. of 

 water, and add 2 or 3 drops of a cold saturated solution 

 of potassic chromate. IS'ow, allow the solution of argen- 

 tic nitrate to flow from a burette, graduated into ^\^^ c.c, 

 into one of these solutions, slowly and with constant stir- 

 ring ; each drop as it comes in contact with the liquid 

 produces a red precipitate, which, at first, disappears when 

 mixed with the. rest of the solution, but finally the addi- 

 tion of a single drop causes the red color to remain per- 

 manent ; all the chlorine has united with the silver. 



A solution of argentic nitrate is to be made, one litre 

 of which will exactly precipitate the chlorine in 'L of 

 an equivalent of sodic chloride expressed in grammes, or 

 5.85 grms. If the amount of sodic chloride in the solu- 

 tion tested in this first experiment was 0.11 grm., and 



