about 1 c. c. of the ordinary platinic chloride solution and evaporate 

 on the steam or water bath according to the usual method for 

 determination of K 2 O, being careful to trail the liquid around the 

 side of the dish as it becomes concentrated and to remove just before 

 dryness, so as to have the evaporation completed during the cooling 

 of the dish. This procedure insures a very perfect formation of 

 crystals of the double salt. To the dish is now added about 20 or 

 30 c. c of acidulated alcohol. The preparation of this reagent will 

 be described later. The dish is allowed to stand 3 or 4 minutes 

 with an occasional stirring, then decanted into a 7 cm. filter. The 

 salt is now washed into the filter with 90 per cent alcohol, as usual, 

 until free of platinic chloride. Now wash with the ordinary Lindo 

 solution of ammonium chloride (200 grams per liter of water), using 

 about 20 c. c., and allow these washings to mix with the previous 

 filtrate. The filtrate is stirred and set aside overnight to allow the 

 ammonium platinum chloride to settle. The salt in the filter is then 

 washed with 90 per cent alcohol until free of ammonium chloride. 

 The filter is then dried and the contents washed through with 

 boiling water into a previously weighed small platinum dish, which, 

 after evaporation and drying in a bath for thirty minutes at 100 C., 

 is weighed. The calculated weight of the K 2 O is to be divided by 

 160 grams. This is to be expressed in parts per million, a part per 

 million being the equivalent of the fourth .decimal place in percentage. 



The acidulated alcohol is prepared by conducting HC1 gas into cool 

 90 per cent alcohol until 1 c. c. of the alcohol neutralizes about 

 2^ c. c. of normal alkali, using phenolphthalein as an indicator. 



The method of acidifying is as follows : 



Put 200 or 300 c. c. of strong HC1 into a rather large flask, con- 

 nect by means of a glass tube with a flask holding about one-half 

 liter of 90 per cent alcohol, this flask being kept cool by surrounding 

 with ice or running cold water. The tube containing the gas extends 

 to the bottom of the alcohol. A trap is interposed between the flasks 

 to prevent the alcohol running back into the acid in case the pressure 

 is varied. The flask containing the acid is heated moderately until 

 water begins to pass over, when the process is discontinued, to be 

 renewed with a fresh portion of acid if the alcohol is found to be not 

 sufficiently acidulated. The apparatus as used in this laboratory is 

 illustrated in fig. 3. 



After the filtrate from the potash determination above referred 

 to has stood over night, nearly all of the liquid can be decanted 

 into a porcelain dish of 5 or G inches diameter. Then with ordinary 

 alcohol wash directly into a filter, washing two or three times, and 

 adding the washings to the decanted liquid in the dish. Any sedi- 

 ment that may have gone over in the decantation can do no harm. 

 The evaporation should be carried on very slowly on a steam < >r 



