248 Transactions of the Society. 



effect with even approximate certainty the conversion of crystalloid 

 quinidine into colloid quinidine, an exposure to a temperature of about 

 180° C. for a period of not much less than one hour is required. 

 Whether even then the tendency to revert to the crystalloid form is 

 entirely overcome, time alone can show ; but at any rate it seems 

 proved that the stability of quinidine as a mounting material is very 

 considerably increased by the above process. 



Enough quinidine for a large number of preparations may be thus 

 treated and poured out on a slab ; when cool, it may be broken up 

 and kept in a bottle for use. 



I may just add that I have treated piperine in a similar way with 

 precisely similar results ; and I have a hollow prism filled with 

 piperine, and also a detached lump of it, made in October 1898, 

 which have remained quite unaltered up to the present time, though 

 the surface has been scratched to promote crystallisation if possible. 

 But piperine, though interesting to physicists on account of its very 

 high refractivity and its quite extraordinary dispersive power, is, 

 owing to the latter property, not very suitable for mounting objects 

 for the Microscope, requiring, as it would do, specially corrected 

 objectives. 



