

IRON. 



iron wire, the iron becomes converted 

 'into an oxide, while hydrogen gas passes 

 out at the other end of the barrel. The 

 action of air, assisted by heat, converts 

 iron into a black oxide, containing twen- 

 ty-five of oxygen. By the action of strong- 

 er heat this becomes a reddish brown ox- 

 ide, containingforty-eight of oxygen. The 

 yellow rust, formed when iron is long ex- 

 posed to damp air, is not a simple oxide, 

 as it contains a portion of carbonic acid. 

 According to M. Chenevix, there are four 

 stages of oxydation of iron: the first, or 

 minimum, white ; the second, green ; 

 the third, black; the fourth, or maxi- 

 mum, red. Thenard admits only three, 

 the white, green, and red. 



The concentrated sulphuric acid scarce- 

 ly acts on iron, unless it is boiling. If the 

 sulphuric acid be diluted with two or 

 three parts of water, it dissolves iron 

 readily, without the assistance of any 

 other heat than what is produced by the 

 act of combination. During this solution, 

 hydrogen gas escapes in large quantities. 



Sulphate of iron is not made in the di- 

 rect way, because it can be obtained at 

 less charge from the decomposition of 

 martial pyrites. It exists in two states, 

 one containing oxide of iron, with .27 of 

 oxygen, which is of a pale green, not al- 

 tered by gallic acid, and giving a white 

 precipitate with prussiate of potash. The 

 other, in which the iron is combined with 

 .48 of oxygen, is red, not crystallizable, 

 and gives a black precipitate with gallic 

 acid, and a blue with prussiate of potash. 

 In the common sulphate these two are 

 mixed in various proportions. 



Distillation separates the acid from sul- 

 phate of iron, and leaves the brown ox- 

 ide ot iron, called colcothar. 



Vegetable astringent matters, such as 

 nut galls, the husks of nuts, logwood tea, 

 &c. which contain the gallic acid, preci- 

 pitate a fine black feculafrom sulphate of 

 iron, which remain suspended for a con- 

 siderable time in the fluid, by the addi- 

 tion of gum arabic. This fluid is well 

 known by the name of ink. See INK. 



The beautiful pigment well known in 

 the arts by the name of Prussian blue, is 

 likewise a precipitate afforded by sul- 

 phate of iron. 



If two parts of alum, and one of sul- 

 phate of iron, be dissolved in eight or 

 ten parts of boiling water, and a solution 

 of prussiate of potash be added as long 

 as any effervescence and precipitation are 

 produced, the precipitate, thoroughly 

 washed by effusion of boiling water, will 

 have a green colour. This is owing to 

 the yellow oxide of iron thrown down 



with the prussiate, which must be dis- 

 solved by adding muriatic acid. The 

 deep blue powder, insoluble in this acid, 

 is then to be washed and dried for use. 

 According to Professor Proust, the iron 

 in Prussian blue contains .48 of oxygen, 

 and is obtained only from a super-ox)ge- 

 nated sulphate; the precipitate from a 

 pure alkaline prussiate and sulphate of 

 iron with a minimum of oxygen being 

 white, and containing only .27 of oxygen. 

 This may explain a fact, observed by a 

 French colourman, who, having mixed 

 some Prussian blue and white lead with 

 nut oil, and set it by for some time cover- 

 ed with water, found the surface only 

 blue, and all the rest white. On pouring 

 it out on his stone, and beginning to grind 

 it afresh, with intention to add more Prus- 

 sian blue, he found the colour gradually 

 returning of itself. Here it might be 

 supposed that the oxide of the prussiate 

 had parted with oxygen to the oil, or the 

 oxide of lead, or both, thus becoming . 

 white, except that on the surface, which 

 was supplied with oxygen from the su- 

 perincumbent water ; and that it recover- 

 ed its colour by attracting oxygen from 

 the air. But on this supposition it would 

 seem, that light must contain oxygen, 

 since the colour of this paint, spread on 

 wood or paper, returned by exposure to 

 light in vacuo, as well as in the open air. 

 The colour of Prussian blue is affected 

 by the contact of iron. Mr. Gill, finding 

 a knife with which he was mixing some 

 Chinese blue acquire a green tinge, ^ 

 spread a little of it, and afterwards a lit- 

 tle Prussian blue, sufficiently diluted, on I 

 the blade of a knife, and with a camel 

 hair pencil took off enough to form a tint 

 on paper, and thus continued till he had 

 taken off', in the first instance, thirty-six, 

 and in the second eighty -six, without add- 

 ing any fresh colour. These tints dif- 

 fered in regular gradation from greenish 

 blue to green, olive-green, yellowish 

 green, yellow, and so on to a buff. 



Concentrated nitric acid acts veiy 

 strongly upon iron filings, much nitrous 

 gas being disengaged at the same time. 

 The solution is of a reddish brown, and 

 deposits the oxide of iron after a certain 

 time, more especially if the vessel be 

 left exposed to the air. A diluted nitric 

 acid affords a more permanent solution 

 of iron, of a greenish colour, or some- 

 times of a yellow colour. Neither of the 

 solutions afford crystals ; but both depo- 

 sit the oxide of iron by boiling, at the 

 same time tha the fluid assumes a gelati- 

 nous appearance. 



Diluted muriatic acid rapidly dissolves 



