Vcnaile Refults hi feparating Carburet from Iran, %11 



SECTION VII. 



ReJleB'ions on the Caiifcs of the variable ^lautities of Carburet of Iron a far Jed by Steel ilijjllved iit 

 the Sulphuric Acid. 



MANY circumftances may influence the carburet of iron by the fame fteel ; and it is 

 not eafy to obtain equal mafles of this fubftance, in two different experiments, from fteel 

 of the fame nature. 



Bergman obtained from o,0O2 to 0,oo8 of carburet of iron from different fteeb. Is it 

 probable that there was really fo great a difference in the proportions of a fubllance to 

 which the Reels owe their qualities, without there having been llkewife a very fenfible 

 difference in their ufual properties .■* 



Among the caufes of uncertainty which may occafion the refults to vary, we may prin- 

 cipally remark the following : i. The greater or lefs concentration of the acid employed to 

 diffolve the iron. 2. Its mixture with water at or before the time of the experiment. 3. The 

 more or lefs confiderable dlvifion of the metal. 4. The length of time during which the 

 folution is effefted. 5. The time during which the depofition of carburet remains in contadl 

 with the liquor after the folution is elfeiled. 



1. It is evident that the more concentrated the fulphuric acid, the more rapid the folu- 

 tion, and the greater the quantity of caloric developed in a given time. 



Now experiment proves that the folution of carbone by hydrogene is in the dire£l pro- 

 portion of the caloric which penetrates it, or at leaft that it follows fome progrelTive ratio 

 of increafe with the temperature. It follows, therefore, that the more elevated the tem- 

 perature during the folution of fteel in acids, the lefs of carbone will remain. It alfo 

 follows that it is advantageous not to ufe an acid too concentrated. 



2. As the too great concentration of the acid is inconvenient for the folution of fteel from 

 which the carburet is to be extracted, it is alfo equally inconvenient to dilute it too much. 

 It is in faft known, that when acids are too much diluted with water, they exert a lefs 

 affinity on other bodies ; and this is the cafe with refpeft to very diluted fulphuric acid, and 

 fteel in a high ftate of divifion. The folution then takes place very flowly ; part of the 

 fteel decompofes the water by its own attraiSlive power, and palTes to the ftate of the 

 black oxide, which cannot be diffolved by diluted vitriolic acid. Hence, inftead of carburet 

 of iron, the refidue confifts of a mixture of this fubftance with the black oxide of the 

 metal. 



3. The duration of the experiment is likewife of confiderable inportance. It may arife 

 from two caufes. The firft is the concentration of the acid. In this cafe, the fulphate 

 of iron which is formed abforbs for its cryftallization the fmall quantity of water which 

 remains, with which it falls down, and entirely ftops the folution. The feeond is the 

 too confiderable weaknefs of the acid, the particles of which being feparated too far from 

 thofe of the metal by the water which retains them, cannot in this cafe ad but very flowly. 



I am well convinced that whenever the carburet of iron remains in contact with the me- 

 tallic folution, particularly when it contains difengaged acid, it is fubjccft to remarkable 

 changes. Its black colour becomes yellow, or ycllowifh grey, and it diminiflics in volume 

 by the ailual lofs of part of its mafs. From thcfc obfervations it follows, that in order to 



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