OTHER GLUCOSIDES 185 



to the ferrous condition, and so giving rise to the formation 

 of Turnbull's blue. 



If boiled with, acetic anhydride, alone or in presence of 

 sodium acetate or zinc chloride, the saponins are converted 

 into acetyl derivatives which are no longer toxic. On boiling 

 the acetyl derivatives with alcoholic potash the acetyl groups 

 are removed, but the resulting compound is not identical with 

 the original saponin. 



When treated with a hot saturated solution of baryta a 

 saponin is precipitated in the form of a barium compound. If 

 this latter is treated with the requisite amount of sulphuric 

 acid the barium may be completely removed, but the resulting 

 substance, unlike the original saponin, is physiologically 

 inactive. 



Reactions. 



The following reactions are made use of in demonstrating 

 the presence of a saponin : 



1. Aqueous extracts readily form a froth when shaken up. 



2. Concentrated sulphuric acid gives with all saponins, 

 either in the cold or on warming, a violet or red colour. 



3. Concentrated sulphuric acid containing a little ferric 

 chloride gives with many saponins a blue or bluish-green 

 colour or fluorescence. 



4. The haemolytic action described on page 183 may be 

 tried. 



Although the above reactions are best carried out in the 

 test tube, numbers 2 and 3 may be made use of in micro- 

 chemical work. 



OTHER GLUCOSIDES. 



i 



In addition to the above, there occur in plants a large 

 number of other glucosides which do not readily lend them- 

 selves to reasonable classifications. The exigencies of space 

 will permit of reference only to the following, which are among 

 the more important and more interesting of them. 



SINIGRIN. 



Sinigrin, or myronate of potash, occurs in the seeds of 

 certain Cruciferae, notably Sinapis nigra. 



