IRON. 



of acids are prefent, the metal, although previoudy very tena- 

 cious and duftilc, becomes fo brittle, as not to bear bending 

 to a right angle ; at the fame time that the broken furfaces 

 exhibit a cryllalline frafture That fpecies of form, there- 

 fore, under which magnctifm cxilts, may be brought about 

 by various means. All iron iuftrumcnts, kept in one pofilion 

 for a length of time, become magnetic ; cfpecially if that 

 pofition coincide with the magnetic meridian. We regret 

 that fo little is known on this mtercfting fubjeft ; and for 

 farther particulars refer to the article Magnetlsm. 



Iron combines with feveral of the metals forming alloys, 

 none of which have very ilriking or ufeful properties The 

 alloy of iron ai.d gold has been examined by Mr. Hatchett, 

 who found that 1 1 parts of gold to i of iron formed a malle- 

 able alloy, remarkably ductile, fo as to roll into plates, and 

 be capable of being ftampe^l into coin. The colonr was of 

 a pale yellowifh-grey, and it was of the fpecitic gravity of 

 t6.88j. The molt fmgular property of this alloy it its 

 increafe of volume by combination. iSefore the union, the 

 bulk was 2799 > ^'^^ afterwards, 2843. The very contrary 

 is the cafe with moft of the other alloys of metals, and agree- 

 ably to Berthollet's doctrine of affinity, we find that the 

 mean fpecific gravity of bodies by experiment, is greater 

 than the arithmetical mean, direftly as the affinity of the 

 bodies. We (hould, therefore, in this inftance conclude, 

 that either the affinity of the metals is trifling, or that the 

 above law is not general. 



The alloy of pure iron with platina has not been effefted 

 from the great infufibility of the two metals. Dr. Lewis 

 alloyed caft iron with platina, as well as flee!. The fpecific 

 gravity of this alloy, contrary to the lall, was greater than 

 the arithmetical mean. It was very hard and tenacious, 

 poiTeffing fome degree of duAility. 



After being kept ten years, it was little tarnifhed. 

 Iron is eafily alloyed with filver. In equal parts they 

 form a compound of confiderable duftility, of the colour 

 of the latter metal, but much harder ; and is attra£led by 

 the magnet. The metals feparate, in fome degree, when 

 kept in fufion ; but, according to the experiments of Mor- 

 veau, not completely ; the filver retaining fome of the iron, 

 and the iron fome of the filver, by which its quality, as a 

 metal, is much improved. Iron is not eafily combined 

 with copper in large quantity. We find, however, that 

 thefe metals are capable of uniting, and the alloy is, in fome 

 degree, magnetic. Indeed, in forming certain inftruments 

 of brafs, where the magnetic needle is employed, they are 

 frequently defeftive from this circumllance. To free cop- 

 per entirely from iron, it fhoulJ be rediCTolved in an acid. 

 The oxyd, after precipitation, fhould be diflblved in aqua 

 ammonia, and the alkali then diftilled from it. This being 

 afterwards treated in a clofe vefTel with fome inflammable 

 matter, the metal will be obtained pure. The alloys of tin 

 and iron, and that of iron with zinc, may be formed by 

 mixing clean iron-filings, or turnings, with thofc metals 

 while in a ftate of fufion. Thefe compounds are not of 

 any ufe. Iron may be foldered with feveral of the metals. 

 Copper, gold, and filver, unite to it with great facility ; but 

 require the preferce of borax to keep off the air. 



The moll permanent folder for iron is the carburet of 

 rhe fame metal, called N i, pig-iron. The pig-iron lofes 

 fome of its brittlenefs, and the malleable metal becomes 

 much harder. It does not appear improbable that fteel 

 might be formed by uniting thefe two fiibltances together 

 in certain proportions. 



We have next to treat of the falts of iron, or its combi- 

 nations with acids. 

 Vol.. XIX. 



SulfBat of /ran.— Sulphuric acid does not combine with 

 iron in its metallic form ; in conformity with the general law 

 that no acid unites with a metal till the latter is previoully 

 oxydated. Iron is but fiightly aited upon by this acid in 

 the cold ; but with a degree of heat far fhort of boiling, 

 the iron takes from it a portion of oxygen, converting it 

 into the fulphurous acid, which efcapes in the form of gas. 

 The iron, thus oxydized, combines with another portion, 

 and forms the fulphat of iron. 



When water is added to the iron and the acid, a much 

 more rapid aftion takes place. The metal feizes the oxygen 

 of the water ; hydrogen is evolved ; and the acid unites with 

 the oxyd forming the fait in quellion. When the produd 

 obtained by this means is more than the water can difTolve, 

 it affumes the form of green cryflals, which, when feparated, 

 are the fame with thofe known in commerce and the arts 

 by the names ol green iiitriol and copperas. 



In the aftion of iron upon the concentrated fulphuric 

 acid, it appears anomalous, that the metal fhould not be 

 oxydized with more facility by thii acid, when water is fo 

 rapidly decompofed, the elements of which have fo flrong 

 an attraction for each other. It may appear equally flrange 

 that the water is not decompofed when the acid is not pre- 

 fent. When it is recoUeded, however, that the oxyd of 

 iron is not foluble in water, nor fulphat of iron un the acid, 

 it will appear very clear that the two fubflances are both 

 effential to the effect ; the acid promoting the decompofi- 

 tion of the water by taking away the oxyd, and the water 

 taking up the fait, which would be equally obftruftive to 

 the procefs. 



This fait is not commonly obtained by the above procefs. 

 The fulphuret of iron, above defcribed, already confifls of 

 two of its elements, namely, fulphur and iron ; the oxygen 

 and water of cryllallization bemg alone wanting to com- 

 plete the fait under inquiry. For this purpofe, the natural 

 combination of it, or pyrites, is firfl roafled, and then expofed 

 in large heaps under (heds. Thefe heaps are frequently 

 moiftened with water, by which, together with the prefence 

 of the air, the iron and the fulphur become oxygenated, 

 and cryflals of the fulphat begin to form. The water, 

 which is thrown on from time to time, diflblves the fait, 

 and runs into large refervoirs, which are alfo under flieds, 

 to prevent the rain falling into them. This folution, how- 

 ever, does not contain the fait in a fit flate for cryllallization, 

 being too highly charged with oxygen. The liquor is trans- 

 ferred into large boilers, and pieces of old iron put into it, 

 which, by taking up the excefs of oxygen, change the folu- 

 tion from a red to a green colour. When the evaporation 

 has gone on to a certain point, the fait cryllalhzes, and the 

 green cryflals being feparated, are fit for fale. 



When the cryflals are obtained from a clear folution, and 

 are well defined, exhibiting tranfparent rhomboidal prifms, 

 the fpecific gravity of which is 1.8, the fait may be 

 deemed in a flate of purity. It dilfolves in |thi its weight of 

 boiling water, and twice its weight of water at 60'. When 

 kept dry, it is not liable to change in the air ; but if moif- 

 tened it becomes covered with red fpots by the abforption 

 of oxygen, and if it be diflblved in water, it returns to the 

 flate in which it exillcd before boiling with the metallic 

 iron. When the cryflals are heated, tlie fait at fit ft fufes, 

 then affumes the form of white powder, by lofiiig its water 

 of cryllallization. At a red heat the acid begins to fly off'j 

 and ultimately a fine red oxyd is left buhind. It is in thii 

 way the crocus of commerce is prepared. 



According to the analyfis of Bergmann, this fait is cora- 

 pofed of 



SL Acid 



