METHODS USED AT THE HALLE STATION 547 



for excess of barium. The operation is continued with the sul- 

 furic acid until it no longer gives a precipitate of barium sulfate. 

 By the alternate use of the barium chlorid and sulfuric acid the 

 exact neutral point can soon be secured. When this point is 

 reached the liquid is allowed to cool, the flask is filled to the 

 mark, its contents filtered, and of the filtrate 50 cubic centimeters, 

 equal to half a gram of the substance, removed for further esti- 

 mation. 



This quantity is evaporated on a water bath to a sirupy con- 

 sistence in a porcelain dish with 10 cubic centimeters of platinic 

 chlorid. The platinic chlorid solution should contain one gram 

 of platinum in each 10 cubic centimeters. The residue is treated 

 with 80 per cent, alcohol and, with stirring, allowed to stand 

 for an hour. The precipitate is then collected on a gooch, either 

 of platinum or porcelain, washed about eight times with 80 per 

 cent, alcohol, and the potassium platinochlorid dried for two hours 

 at 100. After weighing, the precipitate is dissolved in hot 

 water and the residue washed, first with hot water and then with 

 alcohol. The crucible with the asbestos felt is dried at 100 and 

 weighed. Any impurities which the double salt may. have carried 

 down with it are left on the filter and the weight of the original 

 precipitate can thus be corrected. The weight of potassium pla- 

 tinochlorid is multiplied by 0.1927 and the product corresponds 

 to the weight of K 2 O in the sample. 



(2) Estimation of Potash in Guanos and Other Fertilisers con- 

 taining Organic Substances. Ten grams of the substances are 

 carefully incinerated at a low temperature in a platinum dish. 

 After ignition the contents of the dish are placed in a half liter 

 flask and boiled for an hour with hydrochloric acid and a few 

 drops of nitric acid. The sulfuric acid can then be precipitated 

 directly with barium chlorid, or better, allow the flask to cool, 

 fill to the mark, filter and treat an aliquot part of the filtrate with 

 barium chlorid as described above. The filtrate from the sep- 

 arated sulfate of barium is neutralized with ammonia and all the 

 bases, with the exception of magnesia and the alkalies, precipi- 

 tated with ammonium carbonate, and the mixture boiled, filled to 

 the mark and filtered. From 100 to 200 cubic centimeters of this 



