^328 Mr. Keates on the Anali/sis of Brass. [May, 



analysis ; and it is probable that even that quantity would be 

 lessened by care in conducting the operations. In performing 

 this analysis, it is necessary to drive off the whole of the nitric 

 acid from the solution (A), and to have sufficient excess of sul- 

 phuric acid to prevent the copper from attaching itself too 

 closely to the iron ; in other respects, the excess of acid is not 

 material. The boiling must be continued until such time as the 

 solution becomes colourless, or till it ceases to give any indica- 

 tion of copper by any tests which may be applied. The solution 

 .should be Altered while hot, and the precipitate washed with very 

 dilute sulphuric acid. If the copper can be sufficiently dried 

 without the risk of oxidizing, the fusion of it may be dispensed 

 with ; but if it is thought necessary to melt it, the charcoal 

 powder, after the fusion, should be carefully washed, as minute 

 grains of copper are generally dispersed through it. The iron 

 used for precipitating the copper should be as pure as possible, 

 as frequently an insoluble black substance, which is probably a 

 carburet of that metal, separates during the action of the acid : 

 should that be the case to any considerable degree, so as to 

 interfere with the results, it is highly probable that it would be 

 got rid of by fusing the precipitate. 



Boihng the solution during the precipitation of the copper has 

 many advantages over simple immersion of the iron in a cold 

 solution. By the former method, a complete precipitation is 

 generally obtained in an hour ; while, by the latter, the solution 

 has held copper at the end of four days, and even when a com- 

 plete precipitation has been obtained (which is not often the case), 

 fi portion of the iron deposits in the state both of protoxide and 

 peroxide, which can only be got rid of, at the risk of dissolving a 

 portion of copper with them ; besides which, the copper frequently 

 adheres with such obstinacy to the iron as to render the estima- 

 tion of it impracticable. 



As a menstruum from which to precipitate the copper, sul- 

 phuric acid possesses decided advantages over any which I have 

 tried ; if the alloy contains lead, it is left insoluble in the first 

 instance; also the copper is not reacted upon when precipitated, 

 as is the case when the nitric acid is employed ; the progress of 

 the operation too may be judged of from the colour of the solu- 

 tion. It is probable that the acetic acid might be employed, but 

 I have not made trial of it. 



