318 



On Chemical Tests. 



[Oct, 



be clipped into a solution of protosulphate of iron, a deposit of the pro- 

 toxide of iron takes place on that part which is not combined with car- 

 bonic acid, and turns it of a dark green colour, changing eventually to 

 an orange yellow. Many other metallic solutions, such as the bichlo- 

 ride, and the p r oto and per nitrates of mercury and the nitrate of silver, 

 do the same thing, but the colours' produced by them are different from 

 the foregoing. 



63. JESiI.'SJ, or gelatine, is detected by tan, or tanning, which pro- 

 duces an adhesive m^-ss. An immediate precipitate with tan maybe 

 considered as a pretty certain indication of gelatine. The test acts on 

 albumen also, but not immediately, ?ee 118. Corrosive sublimate does 

 not act on gelatine, but it acts powerfully on albumen. 



69. EsEA!> is detected by sulphuric acid, and by muriatic acid. The 

 sulphuric acid may be free, or in combination as sulphate of soda, or 

 potash. The precipitate by muriatic acid is soluble in twenty-two parts 

 of water at C0° Faht. and in weak nitric acid. It is also soluble in 

 boiling water ana crystallizes on cooling. Alkaline sulphates are good 

 tests for lead See the tables of re-agents. 



«. — The solutions of protoxide of le?>d may be distinguished by their 

 action wilh sulphuric acid which produces a white precipitate; and 

 from alkaline earths by hydrosulphur,et of ammonia* which produces a 

 black precipitate wi h lead, but not with (he earths. 



b. — Sulphate of lead is soluble in pure potash, but very sparingly 

 soluble in dilute acids. Tfcafed with soda on charcoal before the bloiv- 

 jiipe all the salis of lead oive but 'tow ■ or globules of metallic lead. 



c. Carbonate of lime, or of baryta added to a cold solution of nitrate 

 of lead, and nitrate of bismuth, precipitates the bismuth; but if the 

 mixture be boiled both metals are completely precipitated. Lead may 

 be thus separated from the bismuth of commerce, and also from alloys 

 of copper, see 41 a. 



d. Pure protoxide of ler.d is yellow, but its powder has a reddish 

 hue. The best solvent for it is nitric, or acetic acid. When it does 

 not wholly (dissolve in these acids it is impure. The red oxide of lead, 

 is, by a strong heat converted into protoxide of lead : when put into 

 nitric, or acetic acid it becomes brown being partly converted into pro- 

 toxide which dissolves in the acid, and partly into the brown oxide of 

 lead, which if heated gives out oxygen gas, and is changed into the 

 protoxide without going into the intermediate state^of the red oxide. 



e. The following tests act on protoxide of lead in solution as follows. 

 Potash. A white precipitate soluble in excess of precipitate. 



