MECHANICS AND USEFUL ARTS. 



69 



statical pressure they sustain, equivalent to 78 tons per square inch of 

 original area, and the large permanent set they then exhibit : 



In the experiments on the Drought-iron specimens, the flat-ended 

 steel specimen, and the lead specimen, no definite conclusion was 

 arrived at, the material being more or less compressed without any 

 fracture ensuing. Hence it is difficult to draw conclusions from these 

 results, but the great amount of work expended in compressing the 

 wrought-iron specimens amounted in one case to 4,340 foot Ibs., or 

 nearly twice as much as was required to fracture the round-ended 

 specimen of steel. On the other hand, the low statical resistance of 

 lead corresponds with a dynamical resistance almost equally low. The 

 work required to crush similar specimens of cast iron is nearly the 

 same whether the ends be rounded or not, the round-ended requiring 

 rather more work to be expended than those with flat ends. The 

 mean resistance of the specimens of cast iron is 800 foot Ibs. per 

 square inch ; that of the specimen of steel is 2,515, or rather more 

 than three times as much. The conditions which would appear to be 

 desirable in projectiles, in order that the greatest amount of work 

 may be expended on the armor-plate, are, 1. Very high statical 

 resistance to rupture by compression. In this respect wrought iron 

 and steel are both superior to cast iron ; in fact, the statical resistance 

 of steel is more than three times and that of wrought iron more than 

 two and a half times that of cast iron. Lead is inferior to all the 

 other materials experimented upon. 2. Resistance to change of form 

 under great pressures. In this respect hardened steel is superior to 

 wrought iron. Cast iron is inferior to both. The shot which would 

 effect the greatest damage to a plate would be one of adamant, inca- 

 pable of change of form. Such a shot would yield up the whole of 

 its vis viva to the plate struck ; and, so far as experiment yet proves, 

 those projectiles which approach nearest to this condition are the 

 most effective. 



Mr. Fairbairn stated that steel shots might be made at compara- 

 tively small cost. Mr. Bessemer had informed him that if he had a 

 large order he could produce steel shot at very little more than the 

 price of wrought iron. 



Mr. Nasniyth inquired whether chilled and cast-iron shot had been 

 tried. The process of chilling cast iron was a very simple and inex- 

 pensive one ; and if chilling flat-ended shot had not been tried it was 

 very desirable that it should be. Mr. Fairbairn said they had no 

 practical experience in the matter ; but he believed that the shot 

 being chilled only to a certain extent, they would find that the whole 



