Intelligence and Miscellafieous Articles, 79 



ON THE EMPLOYMENT OF INSOLUBLE SALTS IN ANALYSIS. BY 

 M. HORACE DEMAR^AY. 



One class of metallic oxides is characterized by its want of power 

 to saturate acids perfectly, and by the property of not dissolving in 

 these agents unless they are in excess. The oxides of iron, chro- 

 mium, tin, bismuth, and antimony, as well as the oxides of the 

 electro-negative metals, belong to this class. It is possible to 

 precipitate these oxides without the intervention of any powerful 

 affinity. The carbonates of lime, barytes, strontia, or magnesia, 

 when added to a cold solution of peroxide of iron, separate it so 

 completely that the most sensible reagents indicate no trace of it. 

 In this way the peroxide of iron may be separated from the prot- 

 oxide, and also from the oxides of manganese, cobalt, or nickel, with 

 more facility and accuracy than by any other method. The car- 

 bonates of barytes and strontia are to be preferred, on account of the 

 facility with which they are separated from the fluid in which they are 

 dissolved, or from the peroxide of iron with which they are mixed. 

 This process is excellent for procuring oxide of cerium entirely free 

 from peroxide of iron. Oxide of bismuth acts like peroxide of 

 iron ; carbonate of barytes separates it cold and perfectly from per- 

 oxide of copper; lead, manganese, and nickel may be separated in the 

 same manner. Carbonate of barytes precipitates in the same manner 

 the oxides of antimony and peroxide of tin from solution in muriatic 

 acid, and it may be employed to separate lead from copper, which 

 are united in many alloys. The protoxide of tin is not separated by 

 carbonate of barytes ; this process may, therefore, be used to sepa- 

 rate tin from antimony. Oxide of chromium acts like peroxide of 

 iron with carbonate of barytes ; this metal may, therefore, be se- 

 parated by it from the oxides of nickel, cobalt, manganese, and 

 those which have been mentioned when treating of peroxide of 

 iron. If the solution contains peroxide of iron, that will be preci- 

 pitated with the oxide of chromium, and they may be separated by 

 calcination with potash. 



In order to separate iron from chromium, when both are dis- 

 solved in an acid, it is sufficient to saturate the liquor with sulphu- 

 retted hydrogen in order to reduce the iron to the state of protoxide, 

 and then the carbonate of barytes precipitates the oxide of chromium 

 only. 



Both oxides of mercury, when dissolved in nitric acid, are preci- 

 pitated, like the oxide of bismuth, by carbonate of barytes. The 

 carbonates of the alkaline earths have been proposed to separate 

 different oxides ; but the proposal has not met with the attention 

 which it deserves, because the most important circumstance has 

 not been sufficiently observed, which is, the temperature at which 

 the precipitation ought to be effected. The action of these salts 

 varies at different temperatures. Thus, the muriates and nitrates of 

 cobalt, nickel, manganese, zinc, and copper are entirely decomposed 

 by the carbonates of lime and magnesia, but only at a certain tem- 

 perature. Copper and zinc are precipitated first, cobalt and nickel 

 afterwards, manganese the last; but these metals cannot be se- 

 parated from each other by this method. — Journal de Pharmacie, 

 October 1834. 



