On the Heat of Formation of Alloys. 37 



the same maximum value and is obtained with about the same 

 magnetizing force as that given above. 



Fig. 17 shows the magnetizing force giving the maximum 

 permeability at different temperatures. It will be seen that, 

 as in the case of the tungsten alloy, the points lie almost on a 

 straight line. 



1 desire, in conclusion, to express my thanks to Prof. J. J. 

 Thomson for many useful suggestions during the course of 

 the investigation. 



Cavendish Laboratory, 

 Cambridge. 



IT. The Heat of Formation of Alloys. By J. JB. Tayler, 



B.Sc.(Vict.), University College, Liverpool*. 



EXPERIMENTS have been made upon alloys of lead with 

 tin, bismuth, and zinc, and of zinc with tin and mercury. 

 The method employed, which determined the choice of alloys, 

 consists in dissolving (a) the alloy, and (6) the corresponding 

 mixture of metals, in mercury, and measuring the heat of 

 solution in each case. Assuming that the solutions so obtained 

 are identical, the difference between the heat of solution of 

 the mixture and that of the alloy is the heat of formation of 

 the latter. The method is thus not very different in principle 

 from that employed by Dr. Galtf, and probably also that 

 employed in an as yet unpublished research by Mr. Baker 

 in the determination of the heat of formation of brass. 



The calorimeter used is shown in the figure. Four were 

 made, differing only in size and minor details. In the first 

 two the inner vessel (a in the figure) was of such a size that 

 300 grammes of mercury could be used ; the two later ones 

 took 500 grammes. In all cases a was a tube of thin glass 

 held in place in a larger and thicker tube (h) by an india- 

 rubber rinor. The outer tube could be similarly fitted into 

 the bottle c. To reduce radiation the vessels were silvered, 

 a on the outside, b and c on the inside. The calorimeter was 

 closed by an indiarubber stopper which carried a small 

 receptacle d also of glass. An elastic band projected about 

 j 1 ^ of an inch beyond the lower end of d, so forming a 

 pad against which the wooden cone h could be pressed. The 

 latter communicated by a stiff wire with the outside, and 

 could be raised or lowered at will ; when necessary, from a 



* Communicated by the Physical Society : read May 11th, 1900. 

 t Brit. Assoc. Rep. 1898, pp. 787, 788, and B. A. Rep. 1899. 



/ 



