198 PROCEEDINGS OF THE AxAIERICAN ACADEMY 



actual twisting of small magnets in their beds, then the molecular 

 arrangements consequent upon different admixtures of various ingre- 

 dients might produce more heat in one specimen than in another, and 

 thus afford a criterion of the character of the steel. 



We therefore determined to try our experiments on a practical 

 scale, — to employ a powerful alternating dynamo-electric machine, 

 and to submit the specimens of iron and steel, in a very strong mag- 

 netic field, to the alternating currents, in order to develop a lar^e 

 amount of heat in a short time. The dynamo-machine was of the 

 Wilde type, and made six thousand reversals of curient per minute. 

 The currents were passed through a dynamometer, — wliich is described 

 in the Proceedings of the American Academy of Arts and Sciences, 

 1878-79, p. 122, — and also through the coils in which the specimens 

 were placed. A simple arrangement of keys enabled us to throw the 

 coil, enclosing the specimen, into the circuit, and to withdraw it, — the 

 current passsing continuously through the djnamometiT. The latter 

 instrument gave deflections which were proportional to the strength 

 of the currents employed, and to the amount of work done in heating 

 the iron specimens, although the absolute strength of the currents 

 could not be determined without a calculation of the self-induction of 

 the coils and of the dynamo-machine. The specimens of iron were 

 immersed in a cylindrical copper calorimeter filled with mercury, and 

 the space between the walls of the calorimeter and the surrounding 

 coil was packed with infusorial earth, which is a very good non- 

 conductor of heat. The duration of each experiment was one minute. 

 In this time the strength of the current was observed, and the rise of 

 the thermometer was ascertained. During the space of one minute 

 the coil employed did not heat perceptibly. In two minutes, however, 

 the coil was heated, and it was therefore determined to limit the time of 

 the experiments to one minute, and to take the rise of temperature dur- 

 ing that period. The amount of mercury and the pieces of iron were 

 carefully weighed, with a view of using the data quantitatively ; but the 

 subsequent experiments showed that this was impossible, for the heating 

 effort was confined to the outer layer of the iron, and the temperature 

 at the centre of the bar was very much less than that at the exterior. 



In the following table the first column contains the number of the 

 iron, and opposite the number is the analysis. The third column con- 

 tains the weights of metallic cylinders employed. The fourth column 

 gives the current when one coil — called green for convenience — was 

 used; the fifth column gives the temperature for this coil; the sixth, 

 the current for another coil, — red coil ; and the seventh, the tempera- 

 ture for the latter coil. 



