IRON 



963 



ments on the relative strength and other mechanical properties of cast iron, obtained 

 by the hot and cold blasts, are extracted from a report presented to the British 

 Association (1837) by Messrs. Eaton, Hodgkinson and William Fairbairn. 



Of the three columns of numbers, the first represents the strength or other quality 

 in the cold blast iron, the second that in the hot, the third is the ratio of these qualities ; 

 the figures included in parentheses indicate the number of experiments from which 

 the results have been deduced. 



These results contain nearly the whole of the information afforded by the investi- 

 gation. From the numbers in the tables, it will be seen that in Buffery iron No. 1 

 cold blast somewhat surpasses hot blast in all the following particulars : 1, direct 

 tensile strength ; 2, compressive strength ; 3, transverse strength ; 4, power to resist 

 impact; 5, modulus of elasticity or stiffness; 6, specific gravity: while the only 

 numerical advantage possessed by the hot-blast metal is that it bends a little more 

 than the cold before it breaks. In No. 2 the advantages of the rival kinds are more 

 nearly balanced, still rather in favour of the cold blast. No. 3 hot-blast Carron iron 

 resists both tension and compression better than cold blast of the same denomination ; 

 and No. 3 hot blast from the Devon works in Scotland is remarkably strong, while 

 No. 3 cold blast is comparatively weak, notwithstanding its high specific gravity. 

 On the whole it would appear from the experiments, that while the irons of No. 1 have 

 been somewhat deteriorated in quality by the " hot blast, those of No. 3 have been 

 benefited by its mollifying powers ; while those of No. 2 have been but very slightly 

 affected ; and from the evidence brought forward, it is rendered highly probable that 

 the introduction of a heated blast, whilst it has, perhaps, to a certain extent, injured 

 the softer irons, has improved those of a harder nature ; and considering the small 

 deterioration that the irons of the quality No. 2 have sustained, and the apparent 

 benefit of those of No. 3, together with the saving effected by the heated blast, there 

 seems good reason for the process becoming so general as it has done. 



The following general summary of results, as derived from the experiments of 

 Messrs. Hodgkinson and Fairbairn on the transverse strength of hot and cold blast 

 iron exhibits at one view the ultimatum of the whole investigation : 



Dr. Thompson's chemical examination of several samples of hot and cold blast iron 

 is appended to this report. According to the experiments of this distinguished 

 chemist, iron smelted by hot blast contains a greater proportion of iron, and a smaller? 

 proportion of silicon, carbon, and aluminium, than when smelted by cold air. The 

 mean specific gravity of 8 specimens of Scotch cold blast iron No. 1 was 6'7034 ; the 

 mean of 5 specimens of hot blast from the Carron and Clyde iron works was 7'0263, 

 so that> the density of cold-blast iron is less than that of hot. The mean of 6 analyses 

 of cold-blast iron No. 1 gave 3| atoms of iron, 1 atom of carbon, silicon, and alumi- 

 nium ; the proportion of these three constituents being very nearly 4 atoms of carbon, 

 1 atom of silicon, and 1 atom of aluminium ; consequently Scotch cold-blast iron consists 

 of 20 atoms of iron (with a little manganese), 4 atoms of carbon, 1 atom of silicon, 

 and 1 atom of aluminium. The mean of 5 analyses of hot-blast iron No. 1 gave 6 

 atoms of iron and manganese to 1 atom of carbon, silicon, and aluminium, from which 

 it would appear that cast iron smelted with a hot-blast is purer than when the blast 

 is cold. 'iTiis, however, is not the case, as the numerous analyses of both varieties 



