ADULTERANTS. 45 



oration, the ether leaves, almost pure, the benzoic acid 

 which may be recognized by its odor and \'olatility. 



Boric Acid. — When boric acid or borates are not 

 present in quantities sufficient to appreciably increase 

 the ash of the sample, the quantitive determination 

 is difficult. The qualitative test is very delicate. 

 lOO c. c. of the sample are rendered alkaline with cal- 

 cium hydroxid, evaporated and ashed. Calcium hy- 

 droxid is preferred for this purpose because the ashing 

 takes place more rapidly. The ash is dissolved in the 

 smallest possible quantity of strong hydrochloric acid, 

 the . solution filtered and evaporated to dryness. An 

 appreciable loss of boric acid will not occur. The res- 

 idue is moistened with very dilute hydrochloric acid, 

 mixed with tincture of turmeric and dried on the water 

 bath. The smallest trace of boric acid gives to the 

 residue a vermilion or cherry-red tint. 



Concentrated hydrochloric acid gives with tincture 

 of turmeric, a cherry-red color, which, however, disap- 

 pears on addition of water and also becomes bro^\'n on 

 drying, while the boric acid color appears only on dry- 

 ing and is not destroyed unless much water be added, 

 or at the boiling point. The red color adheres strongly 

 to the vessel and may be removed by alcohol. The 

 flame test may be applied to the residue, but it is not 

 delicate. 



Quantitive determinations of boric acid may be 

 made by Gooch's method as described in analytical 

 manuals. Hehner has shown that sodium phosphate 



