334 



On Chemical Tests, 



[Oct. 



102. QUININE, sulphate of, if a solution containing this salt is aci- 

 dulated with sulphuric acid, and solution of hydriodate of potash be 

 added, a yellow precipitate will take place, which will gradually be- 

 come of a greenish colour, and finally change to reddish brown. 



a. Pure sulphate of quinine when deprived of its water of crystalliza- 

 tion by a heat of 212° should lose only from 8 to 10 per cent of water. 

 This salt is often adulterated by sugar, gum, starch, ammoniacal salts, 

 and earthy salts as the sulphates of lime, and magnesia, and the acetate 

 of lime. Gum and starch are left undissolved when the impure sulphate 

 of quinine is digested in strong alcohol. 



103. RESIN is detected by nitric acid. When concentrated nitric acid 

 is repeatedly digested with gum, gluten, jelly, or other immediate vege- 

 table products, it converts them partly into oxalic acid ; but true resin 

 suffers no such change, it merely becomes a pale, porous, orange colour- 

 ed mass, see 1 : 13 a. 



104. RHODIUM. Pure metallic rhodium is not soluble in any of the 

 acids, but in alloys it dissolves with other metals. With ammonia, 

 potassa, soda, or muriate of platina it gives a yellow precipitate : and 

 a brown precipitate with sulphuretted hydrogen and hydrosulphuret of 

 ammonia. There are two oxides : the protoxide black, and the perox- 

 ide yellow. Henry says it is not precipitated by ferrocyanate of potassa, 

 muriate of ammonia, hydrosulphuret of ammonia, nor by carbonated 

 alkalies. 



a. The salts of rhodium have as yet been but imperfectly examined : 

 those containing the peroxide are mostly of a red, or orange colour ; 

 they are precipitated by cyanuret of mercury, by ferrocyanuret of potas- 

 sium and by muriate of ammonia. The action of the pure alkalies on 

 them is very indefinite. The perchloride of rhodium yields a difficultly 

 soluble, dingy, yellow precipitate with excess of ammonia : muriatic 

 acid redissolves it, and forms a red solution. 



105. SILICA, is soluble in hydrofluoric acid, and forms silicated fluo- 

 ric acid gas ; it dissolves in no other acid after the silicate has been ig- 

 nited. Before the blow-pipe silicic acid is best distinguished by its 

 fusing into a perfectly clear bead with soda on charcoal ; carbonic acid 

 gas being at the same time disengaged with effervescence. 



a. Of siliceous mineral 20 or 30 grains may be conveniently decom- 

 posed in the following manner. Prepare a leaden vessel of about 6 in- 



