The Strength of Materials as Applied to Engineering. 157 



frost, instead of weakening iron, on the contrary strengthens it. 

 That this should be ;50, in respect to axles and rails in extreme 

 cold, remains yet to be proven. 



Papers on the subject have been read before several socie- 

 ties and associations, one of which I will here introduce and 

 then discuss its merits. 



" Effect of Frost xjvon Iron and Steel — (From ' Nature,'). — From 

 papers read before the Manchester Philosophical Society, Dr. Joule made 

 experiments with iron and steel wires stretched through a freezing mix- 

 ture, so as to be part within and part without. In every case tried the 

 wire broke outside of the mixture, " showing that it was weaker at 50° 

 Fah. than at 13°." Also further experiments on darning needles, sup- 

 ported on steel props '2,% inches apart and weights suspended from the 

 middle. The average breaking weight of six needles at 55' Fah. was 58| 

 oz.,and that of six at 13 degrees was 59| oz. The next experiment was 

 with cast iron " garden nails," 1}^ inches long and % inches thick; they 

 were supported on props Ij^^ asunder and a blunt-edged steel chisel 

 weighted to 4 lbs. 3 oz. was let fall from a given height upon the middle 

 of the nail. Twenty-one cold nails broke and twenty warm ones. " The 

 general conclusion," says Dr. Joule is this: Frost does not make either 

 iron (cast or wrought) or steel brittle, and accidents arise from the ne- 

 glect of the companies to submit wheels, axles and all other parts of their 

 rolling stock to a practical and sufficient test before using them. Mr. 

 Spence also made experiments on cast iron bars of % inch squai'e, sup- 

 ported on knife edges nine inches apart and suspended weights from the 

 centre by means of a knife-edged hook to which was attached a scale 

 pan. The average breaking weight of six bars at 60° Fah. was 4 cwt. 4 

 lbs. and of six bars at 0° Fah. was 4 cwt. 30 lbs.'* being an increase of 33^ 

 per cent." 



Further evidence to the same effect has been furnished by 

 M. Caron of Paris, the result of whose observations on the 

 fracture of car axles, have lately been laid before the Paris 

 Academy of Sciences. He finds, in every case, that the break 

 is due to the bad form of the pieces or the faulty nature of the 

 iron ; and denies that bar iron becomes crystalline and brittle 

 under the influence of winter cold. This denial is based on 

 the following experiments : Several pieces of good bar iron 

 were exposed for four months in an ice factory, to temperature 



