1839.] On Chemical Tests, 289 



9. ACID hydriodic. This acid, or any of the hydriodates may be 

 detected by adding thereto sulphuric, or nitric acid, or chlorine, which 

 sets the iodine Jree ; the iodine may then be recognized by its blue colour. 

 The best way of testing is to add starch to the solution, and afterwards 

 a drop or two of strong sulphuric acid, which will produce the charac- 

 teristic blue colour, if iodine be present. If liquid chlorine be employ- 

 ed it must not be added in excess, for if it is, it destroys the blue colour, 

 and becomes a fallacious test. Chlorine gas may be thrown on the 

 surface of the liquid, and be thus used successfully, producing the same 

 blue appearance, see 63 and 113. 



a Hy.driodate of potass or iodine is acted on by several tests ; but 

 none are so distinctive as the foregoing. Corrosive sublimate forms a 

 fine carmine red precipitate of the bin-iodide of mercury. Acetate of 

 lead thrown down a fine yellow precipitate of the iodide of lead. Pro- 

 tonitrate of mercury precipitates protiodide of mercuty, which is a yel- 

 low pow T der that fades gradually into a dirty brown. Muriate of plati- 

 num produces a brown precipitate of iodide of platinum. 



10. ACID hydro-cyanic, or Prussic acid may be known in its free 

 state by the similarity of its smell to the odour of peach-blossoms. But 

 if the acid is strong, great care should be taken, not to smell it too hasti- 

 ly ; as it is deadly poisonous. To detect it in solution, add first proto- 

 sulphate of iron, and then pure potass slightly in excess, which will 

 precipitate the protoxide of iron. Let the whole be exposed to the air 

 for five or six minutes, and then add sufficient muriatic, or sulphuric acid 

 to re-dissolve the precipitate; and if hydro-cyanic acid be present, 

 there will be a formation of prussian blue. Nitrate of silver is also a 

 test for prussic acid, see 108, b. 



a To ascertain the strength of a solution of this acid, precipitate with 

 nitrate of silver, and dry the precipitate. 100 parts correspond with 

 20.33 of pure hydrocyanic acid. 



b. Both the bitter almond, and the cherry laurel, as well as the flowers 

 and kernels of some fruits, contain more or less of this violently poison- 

 ous acid. 



11. ACID muriatic, chloric or hydro-chloric. These three names 

 may be considered as synonymes for the same acid. Muriatic acid de- 

 tects (a) silver; (6) lead; (c) manganese; {d) ammonia ; (e) carbonic 

 acid. Muriatic acid is detected by sulphuric acid and olher tests, see 

 18, 47, and 108. 



a. Muriatic acid detects and is delected by solution of silver, by a 

 copious white precipitate of the muriate or chloride of silver ; which is. 



