PREPARATION OF SOLUTIONS 559 



case one milligram of the potassium platinochlorid corresponds to 

 one-tenth per cent, of the desired salt. 



By Perchloric Acid. Dissolve 15.7225 grams of the sample 

 in 100 cubic centimeters of boiling water, containing 30 cubic 

 centimeters of concentrated hydrochloric acid, in a liter flask. 

 The rest of the process is identical with that described above for 

 muriate of potash, with the exception that a smaller excess of 

 barium chlorid is required and that instead of 20 cubic centimeters 

 of filtrate, 40 cubic centimeters are evaporated. One milligram 

 of potassium perchlorate equals o.i per cent, of potassium sulfate. 

 The addition of 0.3 per cent, should be made under the same con- 

 ditions as are specified under muriate of potash. 



Estimation of Magnesium Sulfate in Kieserit. Ten grams 

 of the finely powdered kieserit are boiled for one hour in a half 

 liter flask two-thirds full of water. After cooling, from 50 to 

 60 cubic centimeters of double normal potash-lye and 20 cubic 

 centimeters of a 10 per cent, neutral potassium oxalate solution 

 are added, the flask filled to the mark, and after being well 

 shaken and standing for a quarter of an hour, filtered. The re- 

 action is represented by the formula MgSO 4 -(-2KOH=MgO 2 H., 

 -I-K 2 SO 4 . Fifty cubic centimeters of the filtrate are then titrated 

 with one-tenth normal sulfuric acid. To the percentage of mag- 

 nesium sulfate found by this process two-tenths per cent, are to 

 be added as a correction. 



472. Preparation of Solutions. i. Preparation of the Platinic 

 Chlorid Solution. The platinum scrap or recovered waste is 

 dissolved in a porcelain basin on the water bath. Four 

 times its weight of pure concentrated hydrochloric acid 

 is added, and while warm nitric acid is gradually introduced. 

 Use one part of nitric to four parts of hydrochloric acid. When 

 the platinum has been dissolved, the solution is concentrated by 

 evaporation until a drop taken upon a glass stirring rod quickly 

 deposits crystals. On cooling the mass assumes a crystalline con- 

 dition ; it is then taken up with water and filtered. The solution of 

 platinic chlorid is now diluted so that 10 cubic centimeters contain 

 one gram of metallic platinum. Special care is necessary that the 

 solution does not contain platinous chlorid or nitrous compounds. 



