Origin. - Prepared by heating to redness arsenous acid, sodium nitrate, and sodium carbonate. Dissolve the fused mass in water and crystallize. Dissolve crystals in water and recrystallize. It should contain not less than 98 per cent. of pure di-sodium-orthoarsenate.

Description and Properties. - Colorless, transparent, monoclinic prisms, odorless, and having a mild, alkaline taste (the salt is very poisonous). Efflorescent in dry air, and somewhat deliquescent in moist air. Soluble in 1.2 parts of water, very soluble in boiling water, and slightly soluble in cold water. Soluble in 60 parts of boiling alcohol. Sodium arsenate should be kept in well-stoppered bottles.

Dose. - 1/60-1/10 grain (0.001-0.006 Gm.) [5/10 grain (0.005 Gm.), U. S. P.].