276 



On Chemical Tests, 



[Oct. 



ent ammonia will re-dissolve the precipitate ; but if it be mercury, the 

 ammonia will turn it black, or grey, but not dissolve it. 



xxix. e. Add caustic potash in excess : if a yellow precipitate cccurs, 

 the base is peroxide of mercury. 



xxx. /. Add sulphate of iron : should a brown precipitate be formed 

 it may consist of metallic gold.* ' 



xxxi. g. Add sulphuric acid, or the solution of a sulphate, if a white 

 precipitate takes place the base is oxide of lead. 



xxxn.If the precipitate formed by the liquid sulphuretted hydrogen is 



Milk white ... .the base is .... Peroxide of iron. 



Dark brown... . do Protoxide of tin. 



Orange red do Protoxide of antimony. 



Yellow.. ...... do Peroxide of tin, or oxide 



of cadmium, but to distinguish which of these last two bases is 

 indicated, proceed as follows : 



xxxni. h. Neutralize the solution with ammonia, then add hydrosul- 

 phuret of ammonia, and if a yellow precipitate falls, which is not solu- 

 ble in an excess of the hydrosulphuret of ammonia, the base is oxide of 

 cadmium; but if the precipitate is easily dissolved in excess of hydro- 

 sulphuret of ammonia, then, the base is peroxide of tin. 



xxxiv. This completes the examination of Nosr 14 to 25 for the base, 

 or metal : but if peroxide of tin ; protoxide of antimony, and arsenic 

 acid, be all of them present in solution, it is difficult to discriminate 

 these three substances with certainty, and to demonstrate their co-exis- 

 tence. Other tests must then be employed to corroborate and confirm 

 the foregoing indications. See the several articles, antimony: arsenic : 

 tin. 



Second.— Examination with Hydrosulphuret of Ammonia. 



xxxv. If the acid solution of the substance under examination gives no 

 precipitate with liquid sulphuretted hydrogen, the base is not one of 

 those just examined, viz. 14 to 25. Another portion of the solution 

 should then be neutralized with ammonia, put into several other test 

 tubes, and be proceeded with as follows: 



xxxvi. J. If on adding hydrosulphuret of ammonia a precipitate is pro- 



8. Alumina. duced, the base is contained in from No. 8 



10 o r x 0 !°?inc manganese ' t0 I3 ' and if the P reci P ita te is black, the 



li! Ox'-, cobalt base is No. 11, 12, or 13. These three 



12. Ox : nickell. 



13. Protox-.iron. may be distinguished, one from the other, by 



the following experiment. 



* 



• Gold is dissolved only by nitro-muriatic acid. 



