UBKMI8TBT. 



[iHOX LKAD. 



oxide enter* into the state of '.-. Green con- ' 



peras is a proto-iulphate of iron in an impure nt.tto. It 

 kl.-iin.iit in in iu y kind* of coal, *c., after exposure to 

 the air, by which mean* the sulphide is gradually con- 

 verted into the sulphate. In the We of Sheppy, at the 

 mouth of the Thames, the proem goes on at an enor- 

 mous rate; for the soil abounds in nodules of iron 

 . are continually undergoing decomposi- 

 tion. Sulphate of iron is also found in many mini-nil 

 spring* ; and frequently the oxygen it absorbs from the 

 atnwphcre, i* the cause of the reddish-brown powder 

 observed when such waters are allowed to remain still 

 for a time. A solution of proto-sulphato of iron, from 

 iu great attraction for oxygen, is often employed with 

 tho nitric oxide*, in the estimation of the presence of 

 oxygen in air, Ac. The proto and per-sulphates are 

 largely used a* fixing agent* in photographic processes. 

 The nitrate of iron U also umuarly employed, and i* 

 produced when iron is dissolved in nitric acid. 



Coppers* (the proto-sulphato) i* much employed as a 

 dyeing agent for producing, with logwood, gall-nuts, 

 sumach, *c., various shades of shite and block colours; 

 and, for the same reason, it U used by calico-printers : 

 but for these purposes the acetate U generally preferred, 

 a* it is more readily decomposed by the gallic acid found 

 in the vegetable substance* we have named. The acetate 

 may be prepared by decomposing the sulphate by means 

 of acetate of lead, when sulphate of lead U precipitated, 

 and acetate of iron held in solution. Acetic acid and com- 

 mon vinegar, or sour beer, Ac. , may be left to digest on old 

 ir.ui hoops or other articles ; which is, of course, a more 

 economical, although slower, process for forming the 

 aorta hi These, and many other salt* of iron, such a* 

 the citrate, succinite, Arc., to which we might direct 

 attention, are not, from their comparative rarity, of 

 general importance. The citrate is employed in medi- 

 cine, and the succinate a* a chemical test 



The combination of iron with cyanogen, however, de- 

 serves by no mean* a passing notice, as the prussiate 

 salt* are extensively used a* a dyeing agent, and are 

 constantly employed in the laboratory as tests, <tc. The 

 cyanide of iron is obtained by adding cyanide of potas- 

 sium to a solution of proto-sulphate of iron ; and is, at 

 first, a white powder. As, however, every salt of iron, 

 miles* in a peroxidised state, has a great attraction for 

 oxygen; the cyanide, if exposed freely to the air, be- 

 come* of a blue colour. The most important cyanide of 

 iron is that generally known by the term of yellow prus- 

 aiate of potau. It consult* of lemon-coloured crystals, 

 of a regular form. This substance is produced on a 

 large scale in this country for the use of dyes. Animal 

 matter, such as hoofs, horns, old leather, blood, &c., is 

 projected into a Urge iron pot heated red-hot, potash 

 and old iron being also added ; a general decomposition 

 ensue* ; and when perfect fusion is effected, the mass i* 

 raked out, and, after being cooled, is dissolved in water, 

 and, subsequently, crystallisation produces the yellow 

 prussiate. During the process, a combination is effected 

 between the carbon, nitrogen, iron, and potass. A new 

 substance U thereby generated, termed ferro-cyanogen, 

 which, with hydrogen, forms hydro-ferrocyanic acid ; 

 analogous, in some respects, to hydrocyanic acid. But 

 the actual composition of the yellow prussiate is that of 

 1 equivalent of ferro-cyanogen ; 2 equivalents of cyanide 

 of potassium ; and 3 of water : hence it is termed ferro- 

 cyanide of potassium. 



Many year* ago we had occasion to notice the acci- 

 dental production of Prussian blue which we shall pre- 

 sently describe whilat visiting some gas-works. Now 

 coal contains carbon, nitrogen, iron, A-c. ; and at the 

 present time, the pnusiato is produced by the union of 

 these element*, in a similar way to that which we named 

 a* accidentally occurring ; charcoal, air, oxide of iron, 

 and carbonate of potash being heated together in suit- 

 able arrangement*. 



The yellow prussiate of potass is converted into tho 

 red, or fern-cyanide so called in contnulistiic 

 th ferro-cyanide, which we have just described by pass- 

 lug chlorine ga* through an aquuou* solution of the 



latter salt, by which means one equivalent of chloride of 

 potassium is removed. It is chiefly used as a test !--r 

 iron, giving a distinctive character as to the oxidation of 

 the iron in the solution tested. The uses of the yellow 

 and red pmssiates, in this respect, will be considered 

 1111. 1. -r the head of Chemical Analysis. 



By adding solutions of the yellow prussiate of potass 

 to per-snlphate of iron, or to a solution of tho pi 

 sulphate, to which nitric acid has been added, a rich, 

 blue precipitate is produced, termed Prussian blue. It 

 is the formation of this substance in woollen and cotton 

 stuifa, by the successive use of the salts named, that such 

 are dyed of a blue colour for many purposes, instead of 

 by indigo. The colour is, however, turned green, and 

 eventually destroyed by alkalies, and is therefore not of 

 a permanent nature. Prussian blue is largely used as a 

 pigment. If a solution of sulpho-cyanide of potass, pro- 

 duced by heating sulphur, carbonate, and prussiate of 

 potash together to redness, and dissolving the fused 

 mass in water when cold, be added to those of the salts 

 of iron, a deep, blood-red colour is produced. It is 

 highly possible that some such combination as this is the 

 cause of the colour of our blood, as all the necessary ele- 

 ments are present in that fluid. 



We have hitherto confined our attention exclusively to 

 the chemical character of the metal iron and its salts. 

 We must now speak of others, which are of considerable 

 interest, before concluding these remarks. It is well- 

 known that iron has the power of becoming attractive 

 by the loadstone, and that steel is subject to the mag- 

 netic influence to such an extent, as to be able to retain 

 all the characteristics of the magnetic force. This fact 

 adds to the value of iron as a metal ; for by means of it 

 we are enabled to construct the mariner's compass, so 

 essential to navigation in the present day. This sub- 

 ject has already been fully discussed, however, in the 

 section on Magnetism ; to which wo must, therefore, refer 

 our readers for information on the matter. 



LEAD. 



THIS metal is one which has long been employed for 

 various uses by mankind, and, like those previously 

 described, it was well-known to the ancients. Its 

 specific gravity, on an average, is 11 '45; its symbol, 

 Pb ; and its equivalent = 103 7- 



Lead is almost always found in nature in combination 

 with sulphur ; in this state it is called galena ; and it is 

 very generally distributed over most parts of Great 

 Britain, especially in Derbyshire, Yorkshire, and Nor- 

 thumbeiruutd. It is obtained by roasting the ore with 

 coal, and subsequently smelting it : the metal is then run 

 into long bars called "pigs," in which state it is sent 

 into the market. 



It has a bluish colour, and may be polished ; but soon 

 tarnishes, owing to the formation of an oxide on its sur- 

 face ; its presence in solution may be detected by sul- 

 phuretted hydrogen gas. This gas, which in the cause of 

 the offensive smell of drains, immediately turns any so- 

 lution of lead to a dark-brown colour ; hence the reason 

 that white paint is so often discoloured, containing as it 

 does the carbonate of lead. 



Lead is easily molted, bent, and rolled, and is there- 

 fore valuable in forming piping, cisterns, and other 

 vessels. It, however, produces a deadly poison when in 

 a state of solution (as the carbonate iu water), which fre- 

 quently occurs from the use of lead cisterns, <Src., if the 

 water in them be nearly pure. This, at first sight, 

 would seem paradoxical, but is easily explained. At the 

 p.-irt whore the lead, water, and air are in contact, the 

 carbonate of lead is formed. The carbonic acid, gradu- 

 ally absorbed by the water, facilitates the solution of the 

 salt, and so impregnates the liquid with lead. Now this 

 does not happen if the water be hard, because the sul- 

 phate* contained therein form ,-ui insoluble coating of the 

 sulphate of lead, which prevents further action on tho 

 metal. Considerable opposition on this account was 

 made, a few years ago, to the introduction of the 

 of Loch Katrine into Glasgow, as it was considered that 



