Scott. — Resistance of Steel to Mechanical Shock. 515 



there is a considerable increase in the number of molecules, or 

 ions and molecules, and therefore a considerable decrease in 

 temperature, quite apart from that due to chemical energies. 



In connection with Van't HofPs finding that the principle of 

 maximum work stated by Berthelot is the more nearly correct 

 the nearer the temperature of reaction is to absolute zero, and 

 that at absolute zero it would be correct, it is perhaps worth 

 pointing out as a coincidence that the apparent heat-changes due 

 to formation or disappearance of molecules become proportion- 

 ately less as the temperature of reaction is lowered, and vanish at 

 absolute zero. 



If the temperature of solids is proportional to their molecular 

 kinetic energies, then, neglecting the internal-energy factor, the 

 capacity for heat of equal numbers of molecules should be the 

 same irrespective of their masses. Hence the specific heat of 

 solids (other things being equal) should be inversely proportional 

 to their molecular weights. The specific heats of the solid ele- 

 ments, however, are proportional to their atomic weights, which 

 suggests that the solid elements with normal specific heats have 

 the same number of atoms per molecule. 



Art. LX. — The Resistance of Steel to Mechanical Shock, and 

 the Determination of Material suitable for Machinery. 



By Professor Scott, Memb.Inst.C.E., Canterbury College. 

 [Read before the Philosophical Institute of Canterbury, 2nd August, 1905.] 

 From the earliest days the worker in steel has applied some 

 test to insure that his labour might not be expended on worth- 

 less material. The blacksmith tests the quality of the iron 

 he uses by nicking and breaking over the anvil, being guided 

 to his conclusions by the force of the blows necessary to effect 

 the fracture, and by the appearance of the broken surface. 

 This test, crude as it may appear, is, in the hands of an ex- 

 perienced man, a more reliable indication of the suitability 

 of the material for the manufacture of machine-parts than 

 many of those tests which it has been customary for engineers 

 to specify, and which entail the use of a large and expensive 

 plant. In fact, this test, in a standardised form, is an accurate 

 measure of the relative capacity of metals for resisting " shock." 

 The introduction of the systematic testing of the materials 

 of construction is of very recent date, and had its origin in the 

 experiments on the strength of structures so often made by 

 engineers in the. early part of the last century, and rendered 

 necessary by the development of important works at a more 



