12 METHODS OP ANALYSIS. 



washing five or six times. Wash again thoroughly with 80 per cent alcohol 

 and dry the precipitate for thirty minutes at 100 C. The precipitate should 

 be perfectly soluble in water. 



(ft) Muriate of potash. Dilute 25 cc of the solution, prepared according to 

 (2) (a), with 25 cc of water, acidify with a few drops of hydrochloric acid, 

 add 10 cc of platinum solution and evaporate to a thick paste. Treat the 

 residue as under (3) (a). 



(c) Sulphate of potash; sulphate of potash and magnesia, and kainit. Dilute 

 25 cc of the solution, prepared according to (2) (a), with 25 cc of water, 

 acidify with a few drops of hydrochloric acid and add 15 cc of platinum solu- 

 tion. Evaporate the mixture and proceed as directed under (3) (a), except 

 that 25 cc portions of ammonium chlorid solution should be used. 



(d) Water-soluble potash in wood ashes and cotton hull ashes. Use above 

 method, making the solution according to (2) (a), and pay special attention to 

 the last sentence of (3) (a). 



(b) OPTIONAL METHOD. OFFICIAL.** 



(1) PREPARATION OF REAGENT. 



Platinum solution. The platinum solution used is the same as that described 

 under the Lindo-Gladding method. 



(2) METHOD OF MAKING SOLUTION. 



The solution is prepared as directed under the Lindo-Gladding method, omit- 

 ting in all cases the addition of ammonium hydroxid and ammonium oxalate. 



(3) DETERMINATION. 



Dilute 25 cc of the solution made as directed under (2) (50 cc if less than 

 10 per cent of potassium oxid be present) to 150 cc, heat to 100 C., and add, 

 drop by drop, with constant stirring, a slight excess of barium chlorid solution. 

 Without filtering, add in the same manner barium hydroxid in slight excess. 

 Filter while hot and wash until tfce precipitate is free from chlorids. Add to 

 the filtrate 1 cc of 'strong ammonium hydrate, and then a saturated solution 

 of ammonium carbonate until the excess of barium is precipitated. Heat and 

 add, in fine powder, 0.5 gram of pure oxalic acid or 0.75 gram of ammonium 

 oxalate. Filter and wash free from chlorids, evaporate the filtrate to dryness 

 in a platinum dish, and ignite carefully over the free flame, below a red heat, 

 until all volatile matter is driven off. Digest the residue with hot water, 

 filter through a small filter and dilute the filtrate, if necessary, so that for 

 each decigram of potassium oxid there will be at least 20 cc of liquid. Acidify 

 with a few drops of hydrochloric acid and add platinum solution in excess. 

 Evaporate on a water bath to a thick paste and treat the residue with 80 perj 

 cent alcohol, sp. gr. 0.8645, both by decantation and after collecting on a Gooch 

 or other form of filter. Dry for thirty minutes at 100 C. and weigh. 



It is desirable, if there be an appearance of foreign matter in the double salt,) 

 that it should be washed according to the previous method with several portions 

 of 10 cc each of ammonium chlorid solution. 



(c) FACTORS. 



For the conversion of potassium platinic chlorid to potassium chlorid use the 

 factor 0.3071 ; to potassium sulphate, 0.3589 ; and to potassium oxid, 0.1941. 



a The Lindo-Gladding method is preferable In the presence of soluble sulphates. 



