332 Analysis of Scientific Books. 



A bar of zinc is said to answer for distinguishing the ammoniuret 

 of copper from that of nickel. It precipitates the copper in the 

 metallic state, whilst it occasions no change in the solution of 

 pure nickel. 



For separating nickel and cobalt, thej adopt M. Laugier's pro- 

 cess ; who dissolves the oxalates of the two metals in water of 

 ammonia. On exposing the solution to the air, the nickel preci- 

 pitates, while the cobalt remains dissolved. Thus, it is said, a 

 perfect separation can be effected. The details of this process 

 were given some years ago in this Journal ; but we have since 

 found them practically exceptionable. 



The sixth chapter treats of the principal salts, employed as 

 re-agents. The application of acetate of lead, to estimate 

 sulphuretted hydrogen, is one of the best chemical tests. The 

 sulphates and carbonates should have been previously removed by 

 nitrate of barytes. From the weight of the sulphuret of lead, the 

 quantity of sulphur, amounting to -f^, may be computed ; to 

 which fraction, if we add -^g, the sum will denote the weight of 

 the sulphuretted hydrogen. Another very general use of acetate 

 of lead is, the separation of the acids from vegetable juices, or in- 

 fusions. On exposing the saturnine salt to a current of sul- 

 phuretted hydrogen gas, the lead is converted into a sulphuret, 

 and the vegetable acid remains free. By the same acetate, the 

 tartaric acid is distinguished from the pyro-tartaric, the former yield- 

 ing a precipitate of tartrate of lead ; while the latter acid remains 

 in solution. Acetate of lead is sometimes used as a test of sul- 

 phuric acid ; but it is not very delicate. It will not detect 

 ^^^.^^ a quantity sensible to litmus infusion, or even pale litmus 

 paper. Paper, imbued with acetate of lead, is a convenient test 

 of sulphuretted hydrogen. Sub-acetate of lead is incomparably 

 the nicest re-agent for detecting carbonic acid, or a carbonate, in 

 solution. The same salt serves to separate picromel from the 

 bile. For this purpose, we pour into that animal product, first, 

 acetate of lead in excess. The whole of the yellow matter and 

 the resin, fall down, in union with the oxide of lead. This oxide 

 carries with it also, the phosphoric and sulphuric acids, which 

 exist in the bile, in the state of phosphate and sulphate of soda. 

 The liquor being filtered, and the precipitate washed, we pour into 

 the clear solution sub-acetate of lead. The excess of oxide in 

 this salt combines with the picromel, and is deposited with this 

 substance, in the form of yellowish-white flocks. These being 

 thrown on a filter, and repeatedly washed with water, are to be 

 dissolved in dilute acetic acid, and the solution is to be exposed 

 to a current of sulphuretted hydrogen. The lead falls down in 

 the state of sulphuret. By evaporating the supernatant liquid, 

 pure picromel is obtained. 



MM. Payen and Chevallier mention a ready method of 



