ON THE MECHANICAL PROPERTIES OF METALS. 



115 



in those by Mr. Reniiie, which were evidently made on small specimens, 

 which being cast of such limited dimensions invariably produce a hard 

 casting exceedingly difficult to crush ; and as those of Mr. Hodgkinson 

 were made, the first from Devon No. 3, an exceedingly hard and rigid iron, 

 and the others from the Carron No. 3, a comparatively strong iron, and 

 the Coed-Talon No. 2, hot blast, a soft, fine working iron, the difierences 

 under these circumstances may be easily accounted for. 



The Eglinton No. 3 iron, from which the results of the different meltings 

 were obtained, is very similar in character, but rather stronger than the 

 Coed- Talon No. 2. Up to the eighth melting it will be observed that the 

 ordinary power of resistance to a crushing force, namely, about 40 tons to 

 the square inch, is indicated. Afterwards, as the metal increases in strength, 

 from the eighth to the thirteenth melting, a very considerable change had 

 taken place, and we there have 60 instead of 40 tons as the crushing force. 

 Subsequently, as the hardness increases, but not the strength, double the 

 power is required to produce fracture. 



From these results we arrive, in round numbers, at the following con- 

 clusions, viz. — 



Crushing force in tons 

 per square inch. 



1st. In cast iron derived from consecutive meltings,"! 



we have up to the eighth m«hing the ordinary > = 40 

 powers of resistance. J 



2nd. From the eighth to the thirteenth melting, or"^ 



nearly the point of maximum strength, the \ _ 

 power of resistance to strain has increased 

 more than one half. 



And, lastly, from the commencement of deteriora- 

 tion, from the thirteenth to the eighteenth melt- 

 ing, and in which the eastings present a hard V = 80 

 silvery fracture, the powers of resistance are | 

 doubled. J 



These facts are the more interesting as they exhibit some curious pbasno- 

 mena in connection with, not only the mechanical properties of iron, but 

 their chemical affinities ; and my friend Professor C. Calvert, of the Royal 

 Institution of this city, having kindly undertaken to analyse a few of the 

 most remarkable samples of the experiments, I attach the particulars as 

 follows. 



In ihe analyses of these irons, Mr. Calvert observes that the gradual in- 

 crease of silica in the irons as they are progressively reunited are well 

 deserving of attention ; as also, the increased quantity of sulphur and carbon, 

 of which it will be observed by the following results that the increase in all 

 the three substances is progressive from the first to the last meltings, as 

 under. 



60 



In the above analyses there appears to be this remarkable fact, that the 

 increase in the quantity of silicium is much greater than appearances would 



