ANAL YSIS OF POTASH SALTS 139 



the washings are colourless. The residue is dried at 

 100° C. and weighed as KgPtClg. 



{b) In Salts of Potash containing Sulphates. — A 

 weighed portion of the sample (5 grams in the case of 

 sulphate of potash, or 10 grams in the case of kainit or 

 other low-grade salts) is boiled with 20 c.c. of HCl and 

 3CXD c.c. of water. Barium chloride solution is cautiously 

 added, drop by drop, to the boiling solution until the 

 sulphuric acid is completely precipitated. Any slight 

 excess of barium is removed by the addition of the 

 least possible excess of dilute sulphuric acid. The 

 liquid, without filtration, is cooled and made up to 

 500 C.C. A portion is then filtered and 50 c.c. of the 

 solution are treated as above in 128 {a). 



The percentage of potash is returned as KgO. 



K2PtCl6XO.i938 = K20. 



129. Chloride. 



The chloride present in 10 c.c. of the solution is 

 determined by titration with iV/io silver nitrate solution, 

 using potassium chromate as indicator. The chloride 

 is calculated as sodium chloride. 



180. Sulphate. 



Twenty c.c. of the solution are precipitated with 

 barium chloride solution in the usual manner, and from 

 the weight of BaSO^ obtained is calculated the per- 

 centage of SO3 present. 



BaSO^X 0.343 = 503. 



181. Lime. 



One hundred c.c. of the solution are mixed with 50 

 c.c. of ammonium chloride solution, and to the liquid 

 is added a small quantity of ammonia and then 



