1 84 GLUCOSIDES 



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 182 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. 



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 Crucifera^, notably Sinapis nigra. 



Preparation. 



Green gives the following method for its extraction : One 

 kilogram of the seeds of the black mustard is ground to a 

 fine powder, and then extracted with one and a half litres of 

 82 per cent alcohol. The mixture is heated on a water bath 

 until the volume of the alcohol is reduced by about one-sixth, 

 the alcoholic extract is then filtered off, and the residue pressed 



