110 THE MICROSCOPIST. 



nio-phosphate of magnesia. A slower crystallization gives 

 prisms. 



METALLIC OXIDES. 



These may usually be determined by treating a small 

 portion of solution, acidulated with hydrochloric acid, by 

 sulphuretted hydrogen ; another, and neutral portion with 

 sulphuret of ammonium ; and a third with carbonate of 

 soda. 



Antim.ony. Sulphuretted hydrogen throws down or- 

 ange-red precipitate from tartar-emetic solutions, etc. 



Arsenic yields white octahedral crystals of arsenious 

 acid when sublimed. Arsenious acid may be reduced to 

 metallic arsenic by heating to redness in a tube with 

 charcoal and carbonate of soda. A solution of arsenious 

 acid yields octahedral crystals by evaporation, so as to 

 determine with the microscope 1000th to 10,000th of a 

 grain. 



Ammonio-nitrate of silver throws down from an aque- 

 ous solution of arsenious acid a bright yellow precipitate, 

 arnmonio-sulphate of copper a green precipitate, and sul- 

 phuretted hydrogen a bright yellow. 



Mercury. Bichloride of mercury, moistened with a drop 

 of solution of iodide of potassium, assumes the bright 

 scarlet color of biniodide of mercury. A strong solution 

 of caustic potash or soda turns bichloride of mercury yel- 

 low from the formation of protoxide ; but calomel or chlo- 

 ride of mercury is blackened from formation of suboxide. 

 Heated in a reduction-tube with dry carbonate of soda, 

 the sublimate shows under the microscope small, opaque, 

 spherical globules of mercury. Dr. Wormley states that 

 a globule of mercury or "artificial star" may be discrim- 

 inated by the one-eighth objective if it be but the 

 25,000th of an inch in diameter, weighing about the 

 9,000,000,000th of a grain ; globules of 5 ^th of an inch 

 diameter weigh about 70,000,000th of a grain. 



