Conjiieralkns refpeBlng the Oxides af Iron and other Metals. 457 



This obfervation points out a method of retloring the copperas of the (hops to the (late of 

 green fulphate. When. brown depoGtions are formed, it contains copper. 



The folution of fulphurated hydrogcne is not the only practicable means to reduce the 

 blue prufTiate to the (late of white pruffiate. The requifite abftradion of oxygene !« 

 made by keeping PruiTian blue with water and plates of iron or tin in a well clofed veflcl. 

 By this treatment it acquires all the properties of the white pru(riate. 



The diftribution of oxygene between a metal and its oxide is not an uncommon fail in 

 chcmiftry. By keeping a red fulphate or muriate with iron, they are enabled to recover 

 their firft (late. Mercury kept in a folution of corroGve fuhlimate becomes changed, as does 

 likewife the metallic fait itfclf, into the mild muriate of calomel. Mercury undergoes the 

 fame change in a folution of the red muriate of iron, but is not altered in a folution of the 

 green muriate of the fame metal. In the red fulphate, the mercury is converted into that 

 kind of fulphate which does not become yellow by the afFuGon of water, that is to fay, in 

 which the oxide is at its minimum. Many other fads of the fame kind might be 

 mentioned. 



It has been aflerteu in this paper, that the oxygenated muriatic acid does not a£l upon 

 the oxide of PruiTian blue. The following affords a proof of the truth of this affertion : 

 All the known red oxides, whether natural or artificial, colcothar, the iron ore of 

 Elba*, undergo no alteration in this acid ; but the native brown oxides, which for the moft 

 part are mixtures of the black and red oxides, are affedl:ed by fuch treatment. 



It is found by means of tlie oxygenated muriatic acid, that the oxides of the nitrate, 

 the acetite and the muriate of lead are not at their maximum of oxidation. All thefe faks, 

 when kept beneath this acid, are decompofed. A brown or puce-coloured oxide is foon de- 

 pofited, and even cryftallized round the fides of the veflels : and the nitric acid no longer 

 afls upon the new oxide. In procefs of time, however, that acid alTumes a fine rofe colour, 

 bubbles of air rife from the mixture at the bottom, and at length the nitrate is produced, as 

 foon as the oxide, continually folicited to union by the nitric acid, has parted with the dofc 

 of oxygene which oppofed that union. 



The muriatic acid does not diflfolve fuper-oxygenated lead without producing at the fame 

 time abundance of the oxygenated acid ; but in order to procure this oxide in greater quan- 

 tity, it is only neceiTary to treat the minium of commerce with a weak nitric acid, which 

 feparates 13 or 14 per cent, of brown oxide, difcovered, as is well known, by Scheele. The 

 red lead of Siberia is nothing elfe, as Mr. Macquart has (hewn, but a natural fuper-oxida- 

 tion of this metal. It would be intereding to know, whether by carrying the calcination 

 beyond the point which affords minium, it might not be pofhble to render the oxide 

 brown. Such a procefs might perhaps fupply the want of mangancfc, for preparing the 

 oxygenated muriatic acid. 



Mr. Proud defers to a future communication an account of the pature of lead, oxided in 

 a lefs degree than conftitutes the bafis of the nitrate of this metal, . 



From, the foregoing fails Mr. Proud draws the following conclufions ; 



The oxide which alkalis feparate from Prulfian blue is red, though it originally was 

 black in the green fulphate which afforded this blue. 



• The ore of Elba often contains fulphate of iron. It may be e»traftcJ by yeatment with nitric aclj, and 

 fulifcqucnt prccipit.<tion with ammoniac or cauftic pot-afh. 



Vol". I. — January 1798. 3N The 



