644 Lord Kelvin [May 21, 



The composition stated for the alloy in each case is the result 

 of chemical analysis. No. I. was intended to be equal parts of zinc 

 and copper (as being approximately the chemically combining pro- 

 portions) ; but the alloy, which resulted from melting together equal 

 parts, was found to have 4 per cent, more copper than zinc, there 

 having no doubt been considerable loss of the melted zinc by evapo- 

 ration. No. III. turned out on analysis to be, as intended, very 

 nearly in the chemically combining proportions of silver and copper. 

 No. IV. was intended to be equal parts of silver and copper, but 

 analysis showed the deviation from equality stated in the table. The 

 proportions of No. II. were chosen for the sake of comparison 

 with Professor Roberts Austen's result (§ 30), and the agreement 

 (34: -6 and 36) is much closer than could have been expected, con- 

 sidering the great difference of the two methods and the great 

 difficulties in the way of obtaining exact results which each method 

 presents. 



From a chemical point of view it is interesting to see, from 

 Mr. Gait's results, how much more, both in the case of copper and 

 zinc, and copper and silver, the heat of combination is, when the 

 proportions are approximately the chemically combining proportions, 

 than when they differ from these proportions to the extents found in 

 Alloys II. and IV. Mr. Gait intends, in continuance of his investi- 

 gation, to determine as accurately as he can the heats of combination 

 of many different alloys of zinc and copper and of silver and copper, 

 and so to find whether or not it is greatest when the proportions are 

 exactly the chemically " combining proportions." He hopes also to 

 make similar experiments with bismuth and antimony, using aqua 

 regia as solvent.] 



[§ 32. February 1898. — Looking now to column 5 of the table of 

 § 27, we see from Professor Eoberts Austen's result, 36 thermal units, 

 for the heat of combination of 30 per cent, copper with 70 per cent, 

 zinc, and from Gait's 77 thermal units for equal parts of copper and 

 zinc, that the law of electric action on which the calculations of 

 the tables are founded is utterly disproved for discs of metal of one 

 one-thousand-millionth of a centimetre thickness, with air or ether 

 spaces between them of the same thickness, but is not disproved for 

 thicknesses of one one-hundred millionth of a centimetre. 



Consider now our ideal insulated pile (§ 29) of discs 10~^ of a 

 centimetre thick, with air or ether spaces of the same thickness be- 

 tween them. Suddenly establish metallic connection between all the 

 discs. The consequent electric currents will generate 7*4 thermal 

 units, and heat the discs by 79° C. Take again the insulated column 

 with thicknesses and distances of 10~^ of a centimetre; remove the 

 ideal glass separators and diminish the distance to 10~^ of a centi- 

 metre (the thicknesses of discs being still 10~* of a centimetre). Now, 

 with these smaller distances between two opposed areas, make metallic 

 contact throughout the column by bending the corners (the discs for 

 convenience being now supposed square) ; 74 thermal units will be 



