334 METALS AND THEIR COMBINATIONS. 



A dark-brown, almost, black powder, but very sparingly soluble 

 in water, imparting to the solution a weak alkaline reaction. It is a 

 strong base, and easily decomposed into silver and oxygen. 



Antidotes. Sodium chloride, white of egg, or milk, followed by an emetic. 



Complex silver compounds. A great many combinations of silver 

 with organic substances have been introduced and a few are extensively em- 

 ployed in medicine. These compounds usually differ in properties from the 

 inorganic salts of silver. They are antiseptic and less irritating than silver 

 nitrate. 



Argonin, silver-casein, is a soluble casein compound containing 4.28 per cent. 

 of silver. It is a nearly white powder, soluble in water, from which the silver 

 is not precipitated by sodium chloride or hydrogen sulphide. It is also soluble 

 in alkalies, egg-albumin, blood-serum, etc. 



Argyrol, silver vitellin, is a compound of a derived proteid and silver oxide, 

 containing from 20 to 25 per cent, of silver. It occurs as black, glistening 

 hygroscopic scales, freely soluble in water and glycerin, insoluble in oils and 

 alcohol. It is said to be incompatible with acids and most of the neutral and 

 acid salts in strong solution. 



Protargol is a compound of albumin and silver, containing 8.3 per cent, of 

 silver. It is a yellow powder, soluble in 2 parts of cold water. The silver is 

 not precipitated by the usual reagents, such as alkalies, sulphides, chlorides, 

 bromides, iodides, nor by heat. It is compatible with picric acid and its salts 

 and with most metallic salts, but is precipitated by cocaine hydrochloride, 

 which, however, may be prevented by addition of boric acid. It is a non-irri- 

 tant bactericide and antiseptic, extensively used as a substitute for silver 

 nitrate. 



Tests for Silver. 

 (Use a 1 per cent, solution of silver nitrate in distilled water.) 



1. Add to the solution hydrogen sulphide or ammonium sulphide : 

 a dark-brown precipitate of silver sulphide is produced : 



2AgNO, + HaS = 2HNO 3 + Ag 2 S. 



2. Add hydrochloric acid, or solution of any soluble chloride : a 

 white, curdy precipitate of silver chloride is produced, which is in- 

 soluble in dilute acids, but soluble in ammonium hydroxide and in 

 potassium cyanide : 



AgN0 3 + NaCl = NaN0 3 + AgCl. 



3. Add potassium chromate or dichromate solution : a red precipi- 

 tate of silver chromate, Ag 2 CrO 4 , is formed (Plate II., 7). 



4. Add sodium phosphate solution : a pale-yellow precipitate of 

 silver phosphate, Ag 3 PO 4 , is formed, which is soluble in ammonia 

 and in nitric acid. Free phosphoric acid does not give a precipitate. 



