MICROCHEMISTR Y. 83 



glass and then the preparation is allowed to dry slowly. 

 The asparagin then separates out in crystals, among which 

 rhombic plates with an obtuse angle of 129 18' are espe- 

 cially characteristic. This angle measures in the otherwise 

 similar crystals of potassium nitrate 99 44'.* A positive 



O " 



FIG. 26. Crystals of asparagin. FIG. 27. Crystals of saltpeter. 



decision between asparagin and saltpeter is therefore usually 

 possible without the actual measurement of angles, after 

 some practice (cf. Figs. 26 and 27). The observation of the 

 crystals is much aided by polarized light. 



According to the method already employed by C. O. 

 M tiller (I), a solution of diphenylamine may be used to dis- 

 tinguish between asparagin and saltpeter, since the former 

 is dissolved without color, while saltpeter crystals produce a 

 deep blue color with it (cf. 73). The behavior of asparagin 

 crystals on heating is also characteristic. At about 100 C. 

 they are dissolved by their water of crystallization, while at 

 about 200 C. transformation into brown drops of froth takes 

 place. Finally, doubtful crystals may be tested, after Boro- 

 din's method (cf. 71, note), with a saturated aqueous solu- 

 tion of asparagin. 



According to Leitgeb (II, 222), the crystallization of 

 asparagin is hindered by the presence of inulin, as well as 

 of gum, sugar, glycerine, and other viscous fluids. -This 

 author was, however, able to recognize asparagin in D'ahlia 

 roots, which are rich in inulin, after placing transverse slices 

 of them a centimeter thick in 90$ alcohol. After a few days 

 he saw on the cut surfaces well formed crystals, which, after 

 being as completely freed from inulin as possible, showed 

 the above described asparagin reactions. 



* But angles of 109 56' and 118 50' are also possible (cf. C. O. Miiller 

 I, 15); I have, however, never observed these angles, even after a very 

 slow crystallization of pure potassium nitrate. 



