DEFINITION OF TERMS. 



171 



The protoxide of iron may be obtained 

 by four different processes. 1. By keep- 

 ins: iron filings a sufficient time in water 

 at the temperature of 70°. The oxide 

 thus formed is a black powder, formerly 

 much used in medicine under the name 

 of martial ethiops, and seems to have been 

 first examined by Lemeri; but a better 

 process is that of De Roover. He ex- 

 poses a paste formed of iron filings and 

 water to the open air, in a stone-ware 

 vessel; the paste becomes hot, and the 

 water disappears. It is then moistened 

 again, and the process repeated till the 

 whole is oxydized. The mass is then 

 pounded, and the powder is heated in an 

 iron vessel till it is perfectly dry, stirring 

 it constantly. — 2. By making steam pass 

 through a red-hot iron tube, the iron is 

 changed into a brilliant black brittle sub- 

 stance, which, when pounded, assumes 

 the appearance of martial ethiops. This 

 experiment was first made by Lavoisier. 

 3. By burning iron wire in oxygen 

 gas. The wire as it burns is melted, and 

 falls in drops to the bottom of the vessel, 

 which ought to be covered with water, 

 and to be of copper. These metallic 

 drops are brittle, very hard, and black- 

 ish, but retain the metallic lustre. They 

 were examined by Lavoisier, and found 

 precisely the same with martial ethiops. 

 They owe their lustre to the fusion which 

 they underwent. — 4. By dissolving iron 

 in sulphuric acid, and pouring potass into 

 the solution. A green powder falls to 

 the bottom, which assumes the appear- 

 ance of martial ethiops, when dried quick- 

 ly in close vessels. This first oxide of 

 iron, however formed, is always com- 

 posed of 73 parts iron and 27 of oxygen, 

 as Lavoisier and Proust have demon- 

 strated. It is attracted by the magnet, 

 and is often itself magnetic. It is capa- 

 ble of crystallizing, and is often found 

 native in that state. 



The peroxide or red oxide of iron may 

 be formed by keeping iron filings red- 

 hot in an open vessel, and agitating them 

 constantly till they are converted into a 

 dark red powder. This oxide was for- 

 merly called saffron of Mars. Common 

 rust of iron is merely this oxide combin- 

 ed with carbonic acid gas. The red 

 oxide may be obtained also by exposing 



for a long time a diluted solution of iron 

 in sulphuric acid to the atmosphere, and 

 then dropping into it an alkali, by which 

 the oxide is precipitated. This oxide is 

 also found native in great abundance. 

 Proust proved it to be composed of 48 

 parts of oxygen, 52 of iron. Consequent- 

 ly the peroxide, wiien converted into red 

 oxide, absorbs 0.40 of oxygen; or which 

 is the same thing, the red oxide is com- 

 posed of 66.5 parts of black oxide and 

 33.5 parts of oxygen. One hundred parts 

 of iron, when converted into protoxide, 

 absorb 37 parts of oxygen, and the oxide 

 weighs 137 ; when converted into per- 

 oxide it absorbs 52 additional parts of 

 oxygen, and the oxide weighs 189. The 

 peroxide cannot be decomposed by heat; 

 but when heated along with its own 

 weight of iron filings, the whole, as 

 Vauquelin first observed, is converted 

 into black oxide. The reason of this 

 conversion is evident. This 100 parts 

 of peroxide are composed of 52 parts of 

 iron, combined with two different doses 

 of oxygen : 1, with 14 parts, which, with 

 the iron, makes 66 of protoxide ; 2, with 

 32 parts, 'vhich, with the protoxide, make 

 up the 100 parts of peroxide. Now, the 

 first of these doses has a much greater 

 affinity for the iron than the second has. 

 Consequently the 34 parts of oxygen, 

 which constitute the second dose, being 

 retained by a weak affinity, are easily 

 abstracted by the 100 parts of pure iron, 

 and combining with the iron, the whole 

 almost is converted into black oxide : for 

 100 parts of iron, to be converted into 

 black oxide, require only 27 parts of 

 oxygen. The peroxide of iron is not 

 magnetic. It is converted into black 

 oxide by sulphuretted hydrogen and 

 many other substances, which deprive it 

 of the second dose of oxygen for which 

 they have a stronger affinity, though they 

 are incapable of decomposing the pro- 

 toxide. Iron is capable of combining 

 with all the simple combustible bodies. 

 A small mixture of it constitutes that par- 

 ticular kind of iron, known by the name 

 of cold short iron, because it is brittle 

 when cold, though it is malleable when 

 hot. Rinman has shown that the brittle- 

 ness and bad qualities of cold short iron 

 may be removed by heating it strongly 



