SULPHATE OF MAGNESIA. 239 



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 

 removed with blotting paper. When the crystals are dry 

 the Canada balsam, previously made thin with ether, may 

 be applied without heat. 



BORAX, OR BI-BORATE OF SODA, 



is soluble in twelve times its weight of cold and twice its 

 weight of boiling water, and crystallizes in very perfect 

 forms of oblique octohedral prisms. Dissolved in alcohol, 

 and dropped on a slide, it crystallizes immediately. 



BORACIC ACID 



is the acid of the salt borax, and is prepared by mixing 

 three parts of borax dissolved in twelve parts of boiling 

 water with one part of sulphuric acid. 



When a little phosphoric acid is added to the boracic 

 acid, and the solution dropped upon a slide, then laid upon 

 a warm iron plate, most beautiful discs are obtained, which 

 exhibit the cross and coloured rings under polarized light. 



Prom the simple solution of boracic acid we obtain 

 crystals belonging to the doubly oblique prismatic system, 

 having two optic axes. Sometimes, when rapidly crystal- 

 lized, the boracic acid forms arborescent crystals on the 

 slide. 



SULPHATE OF MAGNESIA. 

 (Epsom Salts.) 



The solution will deposit crystals belonging to the 

 rhombic system, and varying in form according to the 

 treatment in crystallizing. They polarize brilliantly with 

 the seienite stage. 



