Objects jor the Microscope. 227 



OXALATE OF AMMONIA. 



This is obtained by neutralizing a solution of oxalic acid 

 with ammonia or its carbonate, and evaporating, which 

 gives long, slender needles belonging to the right rhombic 

 prismatic system, and very brilliant crystals under polarized 

 light. 



SALT OF BRUCTA. 



Using a solution of ammonia with certain salts will give 

 an infinite variety of beautiful crystals ; for instance, a 

 little salt of brucia, diluted and mixed with ammonia, will 

 produce delicate star-like groups of crystals ; and if a 

 solution of sulphocyanide of potassium is used instead of 

 ammonia, the crystals are more feathery, and resemble 

 sheaves of brilliant little lances. 



Solution of hydrochlorate of strychnine with ammonia 

 gives an immediate precipitate of minute prismatic crystals, 

 well defined. 



A solution of quinine with ammonia gives a perfectly 

 amorphous precipitate ; with sulphocyanide of potassium it 

 gives very pretty, irregular groups of circular crystals ; but 

 it is well to allow twenty-four hours for the formation of 

 these, as if hurried they are extremely minute, and not so 

 perfect. 



IODO-DISULPHATE OF QUININE. 



This is sold prepared for examination ; the crystals 

 possess a more intense polarizing power than any other 

 known substance. They are difficult to mount, though the 

 formation is an interesting process, and may be attempted. 

 The salt is prepared by dissolving disulphate of quinine in 

 strong acetic acid, warming the solution, and dropping into 

 it an alcoholic solution of iodine in small quantities at a 

 time, and placing the mixture aside for crystallization. 

 They dissolve in hot alcohol, but are not soluble in cold 

 alcohol or ether. 



To prepare for mounting, a little of the liquid containing 

 the crystals should be placed on the slide, and the liquid 



