108 



Lord Kelvin 



on 



combination for four different alloys, as shown in the following 

 table *:— 



! 



No. Alloy. 



Heat of combination 



per gramme of alloy 



in gramme-water- 



Cent. thermal units. 



I 



II 



Ill 



1 48 per cent, zinc "1 



1 52 „ copper) 



(Approximately chemical combining 

 proportions *. ) 



f 30 per cent, zinc 1 



" \ 70 ,, copper J " 



f 7(V7 per cent, silver 1 



•" \23-3 „ copper/ '" 



(Approximately chemical combining 



proportions*.) 



f 516 per cent, silver j 

 " \4S'-k „ copper/ ' 



77 



346 



18 



7 



* The combining proportions are- - 



(i.) 50'8 zinc with 49'2 copper, 

 and (ii.) 77*4 silver with 22*6 copper. 



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 chemi- 

 cally combining proportions) ; 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 con- 

 siderable loss of the melted zinc by evaporation. 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 3G) is much closer than could 

 have been expected, considering 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 pro- 

 portions to the extents found in Alloys II. and IV. Mr. Gait 



* [May, 1898. — Later experiments with more carefully purified metals 

 have given somewhat different numbers for column 3. — K.] 



