AGRICULTURAL ANALYSIS 



Considerable difficulty, however, was experienced in obtaining 

 satisfactory determinations of potassium associated with sulfuric 

 and phosphoric acids. As Caspari has pointed out, the sulfuric 

 acid must be removed by precipitation as barium sulfate before 

 the treatment with perchloric acid is attempted, and unless the 

 precipitation is made in a strongly acid solution, some potassium 

 is carried down with the barium. Phosphoric acid need not be 

 previously removed, but to secure a nearly complete separation 

 of this acid from the potassium, a considerable excess of per- 

 chloric acid should be left upon the potassium perchlorate before 

 it is treated with the alcohol. When these conditions are care- 

 fully complied with, fairly good results may justly be expected. 

 Below is given a number of the results obtained : 



Compounds used. 



Gram 



Potassium chlorid=o. 10 

 Calcium carbonate=o. 13 

 Magnesium sulfate=o. 13 

 Ferric chlorid =0.05 

 Magnesium sulfate=o.o5 

 Manganese dioxid=o.o5 

 Sodium phosphate=o.4o 



1 The residue showed phosphoric acid plainly when tested. 



2 Only traces of phosphoric acid found in the residue. 



In the last three experiments of the above table the amount of 

 perchloric acid was about three times that required to unite with 

 the bases present, and the phosphoric acid subsequently found 

 with the potassium was hardly enough to appreciably affect the 

 weight, although its absolute removal was found impossible. 



That the magnesia does not produce any disturbing effect, as 

 is supposed by the French chemists, Kreider has proved by the 

 following test : One hundred and fifty milligrams of magnesium 

 carbonate were treated with perchloric acid, evaporated till 

 fumes of perchloric acid appeared, and cooled, when the mag- 

 nesium perchlorate crystallized: But on treating it with about 

 15 cubic centimeters of 97 per cent, alcohol containing 0.2 per 

 cent, of perchloric acid, a perfectly clear solution was obtained. If 

 therefore, a sufficient excess of acid be used, no interference will 

 be caused by the presence of magnesium. 



While it is true that the potassium perchlorate obtained may 



