ARSENIC. 207 



When heated to about 218 C. (424 F.) arsenous oxide is volatil- 

 ized without melting ; the vapors, when condensed, form small, 

 shining, eight-sided crystals ; when heated on charcoal, it is deoxi- 

 dized, giving off, at the same time, an odor resembling that of garlic. 



Arsenous oxide is frequently used in the arts and for manufacturing 

 purposes, as, for instance, in the manufacture of green colors, of 

 opaque white glass, in calico-printing, as a powerful antiseptic for 

 the preservation of organic objects of natural history, and, finally, as 

 the substance from which all arsenic compounds are obtained. 



The official solution of arsenous acid, Liquor acidi arsenosi, is a 1 

 per cent, solution of arsenous oxide in water to which 5 per cent, of 

 diluted hydrochloric acid has been added. 



The official solution of arsenite of potassium, Liquor potassii arse- 

 nitis, or Fowler's solution, is made by dissolving 1 part of arsenous 

 oxide and 2 parts of potassium bicarbonate in 94 parts of water and 

 adding 3 parts of compound tincture of lavender ; the solution con- 

 tains the arsenic as potassium met-arsenite. 



Arsenic oxide, As 2 O 5 (Arsenic pentoxide, Anhydrous arsenic acid). 

 When arsenous oxide is heated Avith nitric acid, it becomes oxidized 

 and is converted into arsenic acid, H 3 AsO 4 , from which the water 

 may be expelled by further heating, when arsenic oxide is left : 

 2H 3 AsO 4 = As 2 O 5 -f 3H 2 O. 



Arsenic oxide is a heavy, white, solid substance which, in contact 

 with water, is converted into arsenic acid. This acid resembles phos- 

 phoric acid not only in composition, but also in forming metarsenic 

 and pyroarsenic acid under the same conditions under which the cor- 

 responding phosphoric acids are formed. The salts of arsenic acid, 

 the arsenates, also resemble in their constitution the corresponding 

 phosphates. 



Arsenic oxide and arsenic acid are used largely as oxidizing agents 

 in the manufacture of aniline colors. 



Disodium hydrogen arsenate, Sodii arsenas, Na 2 HAsO 4 .7H 2 O 

 = 311.9 (Sodium arsenate). This salt is made by fusing arsenous 

 oxide with carbonate and nitrate of sodium. 



As 2 3 + 2NaN0 3 + Na 2 CO 3 = Na 4 As 2 O 7 + N 2 O 3 + CO 2 . 



Sodium pyroarsenate is formed, nitrogen trioxide and carbon 

 dioxide escaping. By dissolving in water and crystallizing, the 

 official salt is obtained in colorless, transparent crystals : 



15H 2 = 2(Na 2 HAsO 4 .7H 2 O). 



