CELL-CONTENTS AND FORMS OF CELLS. 163 



edge of the residue branching groups of needles of caffeine gold 

 chloride separate. Cocaine is another alkaloid which forms char- 

 acteristic crystals, and the double salt of the chloride with palladous 

 chloride is very characteristic (Fig. 97). The crystals of the 

 latter may be prepared in the same manner as caffeine, except 

 that to the sections of coca leaves or the powdered material a 

 smaller quantity of hydrochloric acid is added. 



FIG. 96. Caffeine gold chloride; crystals formed on the addition of a solution of gold 

 chloride to a dilute aqueous solution of caffeine. 



PROPERTIES OF ALKALOIDS. In the microchemical study of 

 the cell-contents it is important to bear in mind that the alkaloids 

 possess certain characteristic properties and give definite reactions 

 with the so-called " alkaloidal reagents." The alkaloids occur in 

 combinations with acids forming salts which are mostly soluble in 

 water or in alcohol, and consequently may be extracted by means 

 of these solvents. From the latter well-characterized crystals 

 may be easily formed. The free alkaloid may be separated from 

 solutions of their salts in water by the addition of alkalies, but it 

 is usually important that the solutions of the latter be not in 

 excess, as otherwise the separated alkaloids may dissolve. With 



