776 A TEXT-BOOK OF BOTANY. 



having been made from Lumiere autochrome plates, using direct 

 sunlight. 



The method of obtaining the crystals was rather simple. The 

 solvents used were distilled water, alcohol, ether, chloroform 

 and a mixture of chloroform and alcohol. To a weighed amount 

 of the substance was added a sufficient quantity of solvent to 

 give a saturated solution. A drop of this was added to a slide 

 which was covered either with a bell-jar or the cover of a Petri 

 dish. If the crystals formed too rapidly, giving rise to crystal 

 aggregates, more dilute solutions were made from the original 

 solution until single crystals were obtained therefrom. In some 

 instances, as with physostigmine salicylate, where the edges of 

 the crystal are likely to be re-dissolved, the slides were finally 

 dried in a desiccator over sulphuric acid. With caffeine gold 

 chloride, the best crystals were obtained when the solutions were 

 relatively weak. Again, it was found that after crystals were 

 mounted in balsam, as cocaine hydrochloride, caffeine gold chlo- 

 ride, etc., the isolated crystals grew considerably in size at 

 the expense of amorphous material. A rather unique instance 

 of growth of large crystals was with menthol when the slide con- 

 taining the silky aggregates was covered with another slide. 

 Finally it should be stated that some patience and experience are 

 necessary to obtain satisfactory crystals. 



WORKS OF REFERENCE. 



Principles of Microscopy. By A. E. Wright. 



Das Mikroskop. By Leopold Dippel. 



Anleitung zur Mikrochemischen Analyse. By H. Behrens. 



Die Botanische Mikrotechnik. By A. Zimmermann. 



Methods in Plant Histology. By Charles J. Chamberlain, 



Elements of Drawing. By John Ruskin. 



For Drawing of Crystals, consult " Crystallography and Practical Crystal 



Measurement," by A. E. H. Tutton. 

 Physical Optics By Robert W. Wood. 



