Affinity and Dissected {Structural) Formula. 407 



h x varies with the nature of the carbon employed; charcoal 

 yielding the highest value, this modification is selected, and the 

 mean value 7*964 taken for h Y : — 



Favre and Silbermann . . 8*080 



Despretz 7*912 



Andrews 7-900 



Mean . . 7*964 



C. One gramme of hydrogen burnt with oxygen to liquid 

 water evolves h 2 heat-units, the materials and products being all 

 examined at 15° and 760 millims. : the mean value 34*275 is 

 taken for h% : — 



Hess 34-792 



Dulong 34-743 



Grassi 34*466 



Favre and Silbermann . . 34*462 

 Julius Tbomsen .... 34*103* 



Andrews 33-808 



Joule . 33-553 



Mean . . 34-275 



12. Hence, if 12m grammes of charcoal, n grammes of hydrogen, 

 and 16p grammes of oxygen were to coalesce, forming 28 grammes 

 of compound, the temperature being 15° and 760 millims. 

 throughout, the heat evolved would be 



2S¥ 15 =l2mh 1 + nh^-2BR 1 . 



Now let h 3 be the heat required to raise one gramme of char- 

 charcoal from 15° to 100°, 

 h 4 be the heat required to raise one gramme of hy- 

 drogen from 15° to 100°under constant pressure, 

 h 5 be the heat required to raise one gramme of oxygen 

 from 15° to 100° under constant pressure, 

 and H 2 be the heat required to convert one gramme of 



compound at 15° into vapour at 100° and 760 

 millims. ; 



then the heat generated by the combination of the carbon, 

 hydrogen, and oxygen at 100° to form vapour at 100° would be 



28Y lw = 2BY ls + 12mh B + nh 4 +l6ph s --28E 2 =l2m(h 1 + h 3 ) 



+ n{h 2 + h 4 ) +I6ph 5 -28(H 1 + U 2 ). 



* Berichte der Deut. Chem. Ges. vol. iv. p. 944. The value found for 

 2*005 grms. of hydrogen uniting with 16 grms. of oxygen to form 18005 



grms. of water is 68*376, whence the value Q'QQfi =34*103 for 1 grm. of 



hydrogen. 



