114 



REPORT 1853. 



On a careful examination of the drawings which exhibit the line of frau- 

 ture of the cubes derived from the different meltings, it will be observed 

 that up to the tiiirteenth melting the whole of the specimens appear to yield 

 at one and the same line of fracture, namely, by wedges which are split, or 

 which slide off diagonally at an angle varying from 52° to 58°. This appears 

 to agree with the experiments of Professor Hodgkinson on the mechanical 

 properties of iron obtained from the hot and cold blast *. In speaking of 

 the angle of the wedge he states, that " We have seen that when bodies 

 are subjected to a crushing force, their fracture, if they do not break 

 by bending, is caused by the operation of a cone or wedge, which seems, 

 under various circumstances, to slide off at nearly a constant angle. If a 

 prismatic body, as for instance a short cylinder, be subjected to a crushiug 

 force, there seems no reason why fractures should take place one way more 

 than another ; there is usually, too, in soft irons a bulging out in every di- 

 rection round the cylinder, which shows that it is equally strained all round ; 

 a matter which is otherwise exemplified in fig. 8. If, then, the cylinder be 

 longer than the wedge, or than the two cones, which are always in operation 

 at the ends during crushing, it is evident that the angle of the wedge and 

 cones, which is the same, will depend upon the nature of tlie material, and 

 the cones nmst be isosceles. Cylinders longer than the wedge usually slide 

 off in one direction without showing the cones." 



The resisting powers of iron, stone, and other materials to a crushing 

 force, have been ascertained by various writers; but the most accurate and 

 extensive — excepting only those of recent date — are probably those by Mr. 

 George Rennie. Rondelet made a considerable number of experiments on 

 stone and wood of various kinds; but those by Mr. Rennie appear to be 

 the most conclusive, and give evidence of the great accuracy with which 

 Mr. Rennie's experiments were conducted. Professor Hodgkinson took up 

 the subject where Mr. Rennie left off; and the experiments recorded in the 

 preceding Tables are to a great extent analogous with those by Rennie and 

 Hodgkinson. It may be interesting, for the sake of illustration, to compare 

 them. Taking the mean of the different meltings as shown in the follow- 

 ing Table, we have an approximate ratio of the forces required to crush 

 cast iron under the separate forms which indicated the experiments made 

 by Mr. Rennie, Mr. Hodgkinson, and myself. 



The comparisons will therefore stand as the numbers 76, 63 and 52. The 

 discrepancies observable in the different experiments may be accounted for j 



* See Report on the Properties of Hot and Cold Blast Iron, Transactions of the British \ 

 Association for the Advancement of Science, vol. vi. 



