INFLUENCE OF CARBONATES 591 



potash by perchloric acid Schenke calls attention to the influence 

 of large quantities of carbonate of lime in requiring that larger 

 quantities of perchloric acid be used in order to secure complete 

 transformation of the lime salts into perchlorate. In each case 

 it is necessary that such a quantity be used that the addition of 

 additional quantities of perchloric acid to the hot concentrated 

 filtrate no longer gives the odor of hydrochloric acid. 70 



Further, it is recommended to add 15 cubic centimeters of 

 alcohol to the warm pasty residue obtained upon evaporation, 

 since the solid cooled residue is very incompletely, or at least dif- 

 ficultly, soluble in alcohol. If the material under investigation 

 contains large amounts of lime as for instance marl, residues 

 from filter presses, etc., it is advisable to separate as much as 

 possible of this lime from the solution before precipitating the 

 potash. In the estimation of potash, according to the perchlo- 

 rate method, in strongly acid, especially sulfuric acid, solutions 

 the long time required is the chief objection. In such cases it 

 is quite important that there shall be two evaporations and in- 

 cinerations in a platinum dish. In order to save as much time 

 as possible, the process is carried on as follows : 



Either sulfuric acid or fuming nitric acid may be used for the 

 solution. The solutions are evaporated carefully to dryness over 

 a small free flame, and thus the ammonium salts driven off. The 

 residue is at first gently, and afterwards gradually more strong- 

 ly heated until a distinct red heat is reached. This incineration 

 does not need to be carried on so carefully as in the case of 

 heating of the alkaline chlorids, since the alkaline sulfates, even 

 when kept for a short time at a low red heat, do not lose any 

 alkali. The ignited sulfates in order to avoid any loss in con- 

 sequence of any shrinking on cooling, are carefully covered and 

 after cooling are digested with hot water with continued rubbing 

 and with a little hydrochloric acid. In all two or three cubic 

 centimeters, of a five per cent, solution will dissolve all soluble 

 material. The contents of the dish are then washed into a meas- 

 uring flask and after heating, treated with a slight excess of a 

 10 per cent, barium chlorid solution. If there is only a slight 

 precipitate of barium sulfate the separation of it by filtration 

 70 Die landwirtschaftlichen Versuchs-Statiouen, 1908, 68 : 61. 



