ELISHA MITCHELL SCIENTIFIC SOCIETY. 37 



ON THE DETERMINATION OF POTASH, 



F. B. DANCY. 



Very discordant results seem to be reached by the agricultural 

 analytical chemists all over the country in the determination of 

 potash in commercial manures and commercial potash salts. Even 

 determinations in chemically pure salts seem to give trouble. The 

 "Potash Committee," of the Association of Official Agricultural 

 Chemists, last year sent out specially prepared samples to various 

 chemists all over the country to get their determinations of potash 

 in identical samples for purposes of comparison. These results were 

 so discordant that they were sent around to the different chemists 

 confidentially, and are still preserved as one of the trade secrets ! We 

 did not find time at the Station to have a hand in those determina- 

 tions (1885), but I have just completed determinations in the ''Pot- 

 ash Committee's " samples of this year (1886), the results of which 

 are very satisfactory and may prove of interest. 



There is a well recognized tendency, oftentimes pointed out, to- 

 wards high results in potash determinations. But I see no reason 

 why, with reasonable care, a determination of potash may not be 

 made as accurately and be as reliable as any other. 



The Committee's samples were six in number: 1 was chemically 

 pure sulphate of potash; 2 was kainit; 3, 4 and 6, so far as could 

 be judged, were acid phosphates with potash; and 5 was a complete 

 manure, ammoniated with an abundance of cotton seed meal. 



It was decided first to make three parallel determinations of KoO 

 in the chemically pure sulphate (No. 1), in slightly different ways. 

 The per cent, of K^O in K0SO4 Fresenius gives as 54.092; more re- 

 cent atomic weights (Clarke in ''Constant* of Nature") make it 

 54.062. 



One gram of the K0SO4 was very carefully weighed out and dis- 

 solved up to 1.000 c. c. in distilled water. Three aliquot portions of 

 100 c. c. each (containing 0.1 gram K2SP4) were measured out into 

 beakers and the volume brought to about 150 c. c. The three de- 

 terminations will be designated by a. b. and c. 



a. Heated to boiling; added Bad-, drop by drop, with constant 

 stirring, in slight excess; filtered\ to filtrate added 1 c. c, strong am- 

 monia (NH4HO) and then, drop by drop with constant stirring, a 

 saturated solution of carbonate of ammonia ((NH4)oC0a) as long 



