OF ARTS AND SCIENCES. 305 



examined with the microscope, the prisms are found to be arranged in 

 globular radiating groups, and are terminated usually by a single 

 rhombic plane at a not very oblique angle to the long sides of the 

 prism ; sometimes a number of other modifying planes are observed, 

 giving a sharp end to the prism. From alcohol it crystallizes in 

 branching needles set at a very acute angle to each other. It melts 

 only at a very high temperature, probably above the range of the 

 mercury thermometer. It is slightly soluble in cold water, freely in 

 hot ; soluble in alcohol ; slightly soluble in cold benzol, chloroform, or 

 glacial acetic acid, freely soluble in tliese solvents, when hot ; almost 

 insoluble in ether ; very soluble in carbonic disulphide. The best sol- 

 vent for the substance is boiling water. An excess of amnionic hy- 

 drate throws down from a concentrated solution a heavy precipitate 

 of the free base, which is white, but the liquid turns dark green ; 

 potassic carbonate gives a similar precipitate, not soluble in an excess ; 

 sodic hydrate in small quantity gives a similar precipitate, but dis- 

 solves it when added in larger quantity, giving a reddish solution. 

 It gives a dull orange-x'ed indol reaction with pine wood. 



VOL. XXIV. (n. S. XVI.) 20 



