50 fHILOSOPHICAL TKANSACTIONS. [aNNO IJQJ. 



is produced in tlie heart of tlie mass. It may indeed be objected, that the metal 

 now brought nearer to the state of malleable iron, may require a greater supply 

 of heat to keep it at the same temperature. It is less fusible, as we are well 

 assured. By referring back to the minutes we observe how very often it 

 was necessary to turn the flame on the mass during this 2d fermentation, in order 

 to keep it in a state in which it could be worked. 



The very copious production of elastic fluids during an hour, and often during 

 a much longer space, for in this instance the jjrocess was remarkably successful 

 and short, does not seem favourable to a late ingenious hypothesis, according to 

 which water is the embodying principle of all elastic fluids. Will it be said, that 

 the pig iron, as being in some sort a calx of iron, contains water ? In annealing 

 crude iron, with or without charcoal, it is well known to increase in all its 

 dimensions. Bars originally straight have been bent like an s, when long ex- 

 posed to heat in circumstances where they could not extend themselves end- 

 ways. This phenomenon may be owing to a very small beginning of this fer- 

 mentative motion, which acts as an internal principle of expansion. Cast iron 

 bars, not in contact wiih charcoal, would, according to this supposition, by long 

 annealing lose of their weight ; or if the heat was too low for the elastic fluid 

 to be discharged from their substance, they would probably blister like steel : an 

 appearance undoubtedly owing to the generation of air. Mr. Home, in his 

 Essay on Iron, somewhere remarks, that on opening these blisters he has heard 

 a whistling noise as of air rushing out. During the whole of this process, fre- 

 quent jets of white sparks, of a dazzling brightness, played from the surface of 

 the metal. They would have afforded an extremely beautiful spectacle but for 

 the inconvenience of looking on so hot a mass. They doubtless arose from the 

 burning of small portions ot iron. 



The workman was clearly of opinion, that the fermentation of hard or white 

 crude iron is less than of grey in this process ; a fact which perfectly coincides 

 with the preceding observations, since that species contains less plumbago, or in 

 other words less matter fit to produce elastic fluids. 



XI. On the Decomposition of Fixed Air. By Smithson Tennant, Esq., F. R. S. 



p. 182. 

 As fixed air is produced by the combustion of charcoal, it has long been 

 thought highly probable that vital air and charcoal are its constituent ingredients. 

 This opinion is confirmed by the experiments of Lavoisier, from which he dis- 

 covered that the weight of the fixed air which is formed during the combustion 

 is nearly equal to that of the vital air and charcoal consumed in the process ; and 

 that the small difference of weight may, with great reason, be attributed to the 

 production of water arising from inflammable air contained in the charcoal. 

 The composition of fixed air therefore seems to be determined, by uniting its 



