554 Prof. Thomson on the Applications of Mechanical Effect 



of zinc is 



1301 + 369-(588-6-|-293), or 788-4 . . . (I.): 

 the thermal equivalent of the part of it which consists of oxida- 

 tion and deoxidation alone is 



1301-588-6, or 712*4 . . . (II.) 



The thermal equivalent which I used formerly is 



769 ... (III.) 



If the opinion expressed by Faraday, in April 1834 (Exper. 

 Researches, 919), with reference to the galvanic batteries then 

 known, that the oxidation alone is concerned in producing the 

 current, and the dissolution of the oxide in acid is electrically 

 inoperative, be true for DanielPs battery, the number (II.) is the 

 thermal equivalent of the electrically effective chemical action. 

 Joule's number (III.) is considerably greater than this, and falls 

 but little short of (I.), the thermal equivalent of the whole che- 

 mical action that goes on during the consumption of a grain of 

 zinc. If we take successively (I.), (II.), (HI.) as the value of 6, 

 and take for e and J the values -07284 and 44758, which were 

 used in my former paper, we find the following values for the 

 product J^e : — 



(I.) 2570300, which would be the electro-motive force (in Bri- 

 tish absolute units) of a single cell of DanielPs 

 battery if the whole chemical action were elec- 

 trically efficient. 



(II.) 2322550, which would be the electro-motive force of a 

 single cell of DanielFs battery if only the oxida- 

 tion and deoxidation of the metals were elec- 

 trically efficient. 



(III.) 2507100, which is the electro-motive force of a single cell 

 of DanielPs battery, according to Joule's experi- 

 ments. 



7. The thermal equivalent of the whole chemical action in a 

 cell of Smee's battery (zinc and platinized silver in dilute sul- 

 phuric acid), or of any battery consisting of zinc and a less 

 oxidizable metal immersed in dilute sulphuric acid, is found by 

 subtracting the quantity of heat that might be obtained by burn- 

 ing in gaseous oxygen the hydrogen that escapes, from the quan- 

 tity of heat that would be obtained in the formation of the sul- 

 phate if the zinc were oxidized in gaseous oxygen instead of by 

 combination with oxygen derived from the decomposition of 

 water. Now the quantity of hydrogen that escapes during the 

 consumption of a grain of zinc is g^^ of a grain (if 32-53, which 

 corresponds to the equivalents used by Dr. Andrews, be taken 



