238 CRYSTALLIZATION. 



ruby red by transmitted common light, and the two broad 

 surfaces are emerald green by reflected light. 



HYDROCHLORATE OR MURIATE OF AMMONIA. 



This salt crystallizes in cubes, octohedra, and trapezohedra. 

 A very little of the powdered salt dissolved upon a slide 

 and heated gives a beautiful exhibition of feathery crystals 

 darting across the field of sight, and breaking into stars and 

 crosses. They do not polarize. 



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 polar- 

 ized light. 



SALT OF BRUCIA. 



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 



