266 On the .Determination of Chemical Affinity. 



water-friction experiments. The following Table (mainly 

 taken from Prof. Gr. C. Foster's article "Heat" in Watts' s 

 6 Dictionary of Chemistry/ 1st Supplement, p. 687) gives the 

 chief of these results expressed in gravitation measure, no cor- 

 rections being made for differences in the value of g at the 

 various localities where the experiments were made, or in the 

 specific heat of water at different temperatures. The last 

 column gives the approximate ratio of the value found to that 

 deduced by Joule from water friction, this latter being taken 

 as 423'5 metre-grammes per gramme-degree Centigrade : — 



Observer. 



Him .... 



Joule .... 

 Violle.... 



>> .... 



,, .... 



» .... 

 Eegnault. 



Method employed. 



Crushing of lead 



Friction of water and brass 



Escape of water under pressure 



Specific heats of air 



Heat produced by electric currents 



„ „ induced currents (aluminium) 



„ „ „ „ „ (copper) ... 



>> j> » >> >» (km) 



» „ » » n (lead) 



Velocity of sound 



Value of 

 J found. 



425-2 



432 



433 



441-6 



429-3 



434-9 



435-2 



435-8 



437-4 



437 



Katio to 

 Joule's 

 water- 

 friction 

 value. 



1-004 

 1-020 

 1-023 

 1-043 

 1-014 

 1-027 

 1-028 

 1-029 

 1033 

 1-032 



On the whole, it is evident that further experiments are de- 

 sirable as to the development of heat in circuits of resistance 

 measured in terms of the B.A. unit by known currents, so as 

 to establish as accurately as possible a connexion between the 

 values of J and of the B.A. unit, so that if the first is assumed 

 to be correctly given by Joule's water-friction value the error 

 (if any) in the B.A. unit can be calculated, or so that the value 

 of J can be determined afresh when the precise value of the 

 B.A. unit is known from further experiments. The writer 

 hopes shortly to be enabled to communicate the results of ex- 

 periments in this direction made by a method differing from 

 that employed by Joule in certain important points, so as to 

 avoid the sources of error existent in Joule's 1867 experiments 

 (Part II.). 



