IRON. 



tlif quantity Increafing with the temperature. If the 

 fiirface be defended by a coatinjj of chalk and a folution 

 oFglue, no change of colour takes place when the heat is 

 applied. In the art of blueing fteel, advantage is taken of 

 this method to make tiic blue ornamenrnl. 



In a liigher ten^.peratui-e the furfacc becomes covered with 

 a fcaly cruft, which is compofed of oxygen and iron ; and in 

 the heat of a fmith's forge, it combines with oxygen fo 

 rapiJIy as to burn, throwing off fparks in bright corrufca- 

 tions. If fmall iron wire be expofed in pure oxygen gas, 

 the end being ignited with a bit of greafed cotton, the metal 

 etiters into briliiant combuftion, and a globule of melted 

 matter is formed at the end of it. The iron fo burnt lofes 

 all its rnetallic properties, by combining with the oxygen ; 

 snd diu-ing this change the phenomena of burning take place. 

 The globule is fo brittle as to be capable of being reduced 

 to powder, and is called the black or vitreous oxyd of iron. 

 Iron has fo great an attraftion for oxygen, that it decom- 

 pofes water even in the cold. When filings of that metal 

 are mixed with water in a veflel connefted with a pneumatic 

 apparatus, an el.iilic fluid is evolved, which is found to be 

 hydrogen. The iron lofes its metallic luftre, and ultimately 

 is converted into the black oxyd before fpoken of. 



If this mixture be in a retort, and the boiling heat ap- 

 plied, tbe iron combines with tlie oxygea of the water with 

 much greater rapidity ; and, of courfe, a much greater 

 quantity of hydrogen is eliminated. This method has been 

 employed to obtain the black oxyd of iron, which was 

 formerly called Marital EtUops. Iron dccompofcs water with 

 very great rapidity, when the fulphurie or muriatic acid is 

 prefent. The acid takes up the oxyd as it is formed by 

 the agency of the water, and a new furface is conRantly 

 prefented. A large quantity of hydrogen is in this procefs 

 difengaged, and it is by the prefent method tliat this gas is 

 procured for filling aeVoilatic machines, and for other pur- 

 pofes. If the oxyd which is taken up by the acid be pre- 

 cipitated by an alkali, and dried inflantly, it will exhibit a 

 fimilar appearance to that obtained by the aftion of water 

 alone. When firft feparated it has a green appearance, which 

 it owes to the prefence of water ; "and this being difTipated 

 by heat, it is left of a dark-grey colour. This oxVd, formed 

 by either of the above procefTes, is c.nlled the prot-oxvd of 

 iron, becaufe it is combined with the firf, or fmalleft dofe of 

 oxygen. According to Prouft and Lavoifier, it confills of 

 73 of iron, and 27 '>f oxygen. 



If the prot-oxyd of iron be expofed to the air in a red 

 heat for a !eng»h of tin.e, it affumes a red colour, and con- 

 ftitutes t':.- fubil-nce known in the arts by the names crocus 

 and cokothar. This change of colour is found to have been 

 caufed by its combinirg with an additional dofe of oy.ygen, 

 and the product is denominated the peroxyd, confili-.g, ac- 

 cording to P.-ouft, of J 2 iron, and 48 oxygen. From the 

 beil chemical authorities, it ajipt-ars that iron tmites with 

 oxygen only In two fixed proportions, conftituting the prot- 

 oxyd and the peroxyd ; although it has been held by fome 

 that there are more varieties. 



■If a bar of iron be heated red-hot, and a flick of fulphur 

 applied to it, a fluid fubllance will drop from its end, which 

 is found to he compounded of fulphur and iron, and in che- 

 miftry is called fulphuret of iron. The fufion of fulphur and 

 iron-fihngs, in a crucible, gives a fimilar produift. The at- 

 traction between thefe fubltances is fo great, that their union 

 in nature is very common. 



Iron-filings, mixed with fulphur, and made into a pade 

 with water, in a certain time become very hot and even pro- 

 duce flame. The mixture is fometimcs buried underground 

 to produce an artificial volcano. This phenomenon, how- 



12t 



ever, does not depend upon the immediate combination of 

 the fulphur walh the iron. The water, which is a confider- 

 able agent, is decompofcd ; the oxygen uniting with the 

 iron to form an oxyd of iron, and with the fulphur to form 

 the fulphui-ic acid, while the hydrogen combines with an- 

 other portion of the fulphur producmg fulphuretted hydro- 

 gen, which occafions the flame in the experiment. 



When iron-filings are heat"d with ful]:)hur, even where 

 oxygen is not prefent, at a little (hort of the temperature of 

 rcdncfs, they combine and produce flame. We are indebted 

 to the afTociated Dutch chemills for this faft, as well as a 

 fimilar experiment with fulphur and copper. 



The artificial compound of fulphur and iron, from the 

 experiments of Prouft, is compofed of 62.5 fulphur 

 37.5 iron 



The native fulphuret is found to contain a greater pro- 

 portion of fulphur. When heated in a clofe veflel, fome of 

 the fulphur fublimes, and may be coUefted in a proper ap- 

 par.atus. By this treatment, it is reduced to the ilate of 

 common fulphuret, and lofes 20 per c.nt. of its weight. It 

 is hence compofed of 50.6 fdphur 

 49.4 iron 



According to fome experiments made by Mr. Hatchett, 

 however, thefe proportions are not regular in fpecimens 

 where the cryilalline form varies. This ingenious cliemill 

 has found a native fpecies agreeing in the proportion of its 

 conllituents with the artificial fulphuret. It is what has 

 been called magnetic pyrites ; and is by this ted of the mag- 

 net diiiinguiflied from the common pyrites, which does not 

 pofi"efs that property. It has alfo another pecidiar charac- 

 ter. If dilute fulphurie or muriatic acid be poured upon 

 it, a rapid aftion takes place, and fulphuretted hydrogen is 

 evolved. This is not the cafe with the fuper-fulphuret till 

 it has been expofed to heat, when it lofes its excefs of ful- 

 phur. The common fulphuret of iron h.-.s bjen employed to 

 make artificial magnets. Mr. Hatchett found mat not only 

 the fulphurets, phofphurets, and carburets, were feparati-ly 

 magnetic ; but fufpecls that certain proportions of all ihcfe 

 may conftitute a maximum of magnetic virtue. 



It is highly probable, that the iron is the only fubllance 

 poflefling magnetifm ; and that the facility with which thefe 

 compound fublhuices become magnetic, may arif? from thj 

 greater eafe with which the particles of iron afluuie the pecu- 

 liar arrangement on which this curious property depci'.ds. 

 That fome arrangem.ent, though perhaps equally myftericus 

 wnth cryftallization, may be the caiife of magnetifm, there is 

 much reafon to believe. By mixing iron-filings with melted 

 refin, and inclofing them in a brafs tube, if a magnet be 

 brrught near to the tube, while the mals is Hill liquid, the 

 whole, when cold, will become a magnet. During the touch- 

 ing of a piece of fteel to make it magnetic, there is little 

 doubt but that a new and peculiar di'pofition takes place 

 amongft tiie particles, notwithftanding the fohd ilate of the 

 n-.etal. The particles of bodies appear to be free to motion 

 in the folid form. We find that iron combines with carbon, 

 while both bodies are in that ftate ; and what is ftill more 

 curious, the compound aft'umes a ditferent cryftalline flruc- 

 ture, according to tlie proportions of the two bodies. Oxy- 

 gen appears, in fome inftauce.«, to alter the intern.al arrange- 

 ment of fohd bodies. If brafs, for example, were to be 

 kept in a damp room, but more particularly where the fun-.es 



