MICROCHEMISTRY. 5'I 



It is more important to note that the reaction may 

 entirely fail, even with large quantities of nitrates, in pres- 

 ence of various substances, as, for example, lignified cell- 

 membranes (cf. Schimper II, 217). It follows, therefore, 

 that the absence of nitrates can never be deduced from ( a 

 negative result of this test. 



74. Brucin gives a bright red or reddish-yellow color with 

 nitrates and nitrites, but this gradually disappears. Molisch 

 (VI, 152) uses for microchemical purposes a solution con- 

 taining .2 gram of brucin in 10 ccm. of concentrated sul- 

 phuric acid, but remarks that this reaction is inferior in 

 clearness to the diphenylamine-reaction. 



75. According to Arnaud and Fade (I), the alkaloid 

 .cincJwnamin (C 19 H 24 N 2 O), obtained from the bark of Remijia 

 purdieana, may be used for the microchemical recognition 

 of nitrates. Its nitrate is almost absolutely insoluble in 

 acidified water and forms beautiful, readily recognizable 

 crystals whose form is, unfortunately, not described by 

 these authors. They immerse fresh sections of the parts to 

 be tested directly in a .4$ solution of the chloride of cin- 

 chonamin which is slightly acidified with hydrochloric acid. 

 The crystals of nitrate of cinchonamin will then be formed 

 within the cells containing nitrates. 



76. Potassium nitrate (KNO 3 ) may also be recognized by 

 covering the sections with a cover-glass, adding alcohol, 

 and then allowing them to dry. The saltpeter then usually 

 crystallizes, chiefly in the form of rhombic plates (cf. Fig. 

 27, 130), which stand out sharply, especially in polarized 

 light. Asparagin also forms similar crystals, but these may 

 be easily distinguished from saltpeter crystals by measuring 

 their angles (cf. 130). Besides, the latter are, of course, 

 easily soluble in a concentrated aqueous solution of aspar- 

 agin, and are not destroyed by heating. They can also be 

 readily tested with a solution of diphenylamine. Borodin's 

 method (cf. 71, note) is inapplicable, on the other hand, 

 on account of the ready solubility of potassium nitrate. 



