392 Royal Society : — On the Change of Form assumed by 



hollow and solid ; immersed, some to one-half of their depth, others 

 to two-thirds ; also on similar cylinders of cast iron, steel, zinc, tin, 

 and gun-metal. , 



The specimens experimented on were all accurately turned in a 

 lathe to the required dimensions, which were carefully noted ; they 

 were then heated to a red heat in a wood-furnace used for heating 

 the tires of wheels. As soon as they had acquired the proper heat, 

 they were taken out and immersed in water to one-half or two-thirds 

 of their depth (as stated in the experiment). The temperature of 

 the water ranged from 60° to 70° Fahr. 



The specimens were allowed to remain in the water about two 

 minutes, in which time the portion in the air had lost all redness, 

 and that in the water had become sufficiently cool to handle. These 

 alternate heatings and coolings were repeated till the metal showed 

 signs of cracking or giving way. 



The dimensions were noted after every five heatings. The cir- 

 cumferences were measured in preference to the diameters, as the true 

 circular form was liable to alter. 



General Results— It will be seen by an inspection of the figures 

 that the general effect is a maximum contraction of the metal about 

 one inch above the water-line ; and that this is the same whether the 

 metal be immersed one-half or two-thirds of its depth, or whether it 

 be nine, six, or three inches deep. With wrought iron the heatings 

 and coolings could be repeated from fifteen to twenty times before 

 the metal showed any signs of separation ; but with cast iron after 

 the fifth heating the metal was cracked, and the hollow cylinder 

 separated all round just below the water-line after the second heating. 

 Cast steel stood twenty heatings, but was very much cracked all over 

 its surface. As respects the change of form of cast iron and steel, the 

 result was similar to that in wrought iron, but not nearly so large in 

 amount. The cast iron did not return to its original dimensions, but 

 the smallest diameter was about one inch above the water-line. 



Tin showed no change of form, there being apparently no inter- 

 mediate state between the melting-point and absolute solidity. Brass, 

 gun-metal, and zinc showed the effect slightly ; but instead of a con- 

 traction just above the water-line, there was an expansion or bulging. 



The effect on wrought iron is best seen in the solid cylinder 

 (figs. 9 and 10), where the displacement of particles just above the 

 water-line appears to be compensated by the bulgings at the two 

 extremities. . 



The specimens of wrought iron were submitted by Mr. Abel (Che- 

 mist to the War Department) to chemical analysis, and he informs 

 me that he found nothing noteworthy in the composition of the 

 metal; nor was there any appreciable difference in the specific 

 gravity of the metal taken from different parts of the specimen. It 

 appears therefore to be simply a movement of the particles whilst 

 the metal is in a soft or semifluid state. 



The following is an account of the experiments, which were 

 carried out under the superintendence of Mr. Butter, Draughtsman 



