358 METALS AND THEIR COMBINATIONS, 



filtered off, while antimonic oxide remains undissolved, and may be dissolved in 

 hydrochloric acid. Both solutions may now be used for making the respective 

 tests for arsenic or antimony. 



Comments. Tests 1, 6, and 3 are sufficient to identify arsenic compounds. 

 Test 3 will detect an arsenite in presence of an arsenate, and tests 4 and 5 an 

 arsenate in presence of an arsenite. Test 10, especially in the modified form, 

 and Test 12 are most often used to detect traces of arsenic. 



Alkali arsenites are soluble in water; all others are either insoluble or diffi- 

 cultly soluble in water. Alkali arsenates and acid arsenates of the alkaline 

 earths are soluble in water. All the salts are soluble in mineral acids. 



Arsenous acid dissociates very slightly, and is therefore a weak acid. Its 

 soluble salts are hydrolyzed to a considerable extent, and show an alkaline 

 reaction. Boiling a solution of arsenous acid or its salts in hydrochloric acid 

 results in a loss of arsenic by volatilization as arsenous chloride. Solutions 

 of arsenic acid or its salts suffer no loss of arsenic in this manner. 



Arsenic acid dissociates very much like phosphoric acid, but to a little less 

 extent than the latter in solutions of equal concentration. Even in high dilu- 

 tion the dissociation is mainly thus : 



H 3 AsO 4 ^ H- -f H 2 AsO 4 '. 

 Further dissociation into HAsO/' and AsO/" ions is very slight. 



Antidotes. Moist, recently prepared ferric hydroxide or dialyzed iron are 

 the best antidotes. Vomiting should be induced by tickling the fauces or by 

 administering zinc sulphate, but not tarter emetic. 



33. ANTIMONY TIN-GOLD PLATINUM MOLYBDENUM. 



Antimony, Sb : = 119.3 (Stibium). This metal is found in nature 

 chiefly as the trisulphide, Sb 2 S 3 , an ore which is known as black anti- 

 mony, crude antimony, or stibnite. 



The metal is obtained from the sulphide by roasting, when it is 

 converted into oxide, which is reduced by charcoal. Antimony is a 

 brittle, bluish-white metal, having a crystalline structure ; it fuses at 



QUESTIONS. Which metals belong to the arsenic group ; what are their 

 characteristics? Which non-metallic elements does arsenic resemble? Men- 

 tion some of the compounds showing this analogy. How is arsenic obtained 

 in the free state; what are its physical and chemical properties; how does 

 leat act upon it? What is white arsenic? State its composition, mode of 

 manufacture, appearance, solubility, and other properties. Which three solu- 

 ns, containing arsenic, are official, and what is their composition ? How is 

 3 acid obtained from arsenous oxide, and which arsenate is official? 

 composition and properties of arsenetted hydrogen, and explain its for- 

 mation. What use is made of it in testing for arsenic ? State the composition 

 realgar, orpiment, Scheele's green, and Schweinfurth green. Give a detailed 

 tion of the process by which arsenic can be detected in organic matter. 

 Describe in detail the principal tests for arsenic. 



