2813.] Imperial Institute of France. 387 



the other products in the worm, must likewise retain a portion of 

 that heat. To remedy these two causes of error, Count Ramford 

 conceived the simple and efficacious idea of beginning his experi- 

 ments at a determinate degree below the temperature of the 

 ambient air, and to stop them when the water of the receiver 

 has reached an equal number of degrees above that temperature ; 

 so that in the first part of the experiment the surrounding air 

 and the azote furnish just as much heat to the receiver as they 

 take from it in the last part of the experiment. 



The cylindrical reservoir of the thermometer has precisely the 

 same height as the receiver ; so that it indicates precisely the 

 mean temperature of the whole water in the receiver. 



Count Rumford, by means of this apparatus, burnt success- 

 sively different combustibles, taking care that the combustion 

 was complete, that no residuum was left^ and that neither smoke 

 nor smell was emitted during the combustion. He found that a 

 pound troy of each combustible, during its combustion, raised 

 the heat of the following quantities of water from the freezing 

 to the boiling point 



White wax 72108 lbs. troy, 



Olive oil 68900 



Oil of colza 70906 



Alcohol 51400 



Sulphuric ether 61178 



Naphtha 55900 



Tallow 6375 



It is remarkable that if we admit the accuracy of the analyses 

 of these substances made by Lavoisier, Cruikshank^ De Saussure^ 

 Gay-Lussac, and Thenard; and if we calculate the heat that 

 would have been produced by the hydrogen and carbon which 

 enter into their composition, if they had been burnt separatelvj 

 we obtain very nearly the same results. 



We cannot make the reader sensible of all the merit of 

 these researches^ unless we were to state the numerous calcula- 

 tions of the author^ which is incompatible Vv^iih the nature of 

 our general view. 



Furnished with this previous knowledge. Count Rumford 

 passed to the quantity of heat evolved by the combustion of 

 wood; bat here the problem became more complicated. A high 

 temperature produces numerous changes in wood. One part of 

 its constituents is driven off, while another enters into new com- 

 binations. It was necessary, therefore, in the first place, to 

 examine the structure of wood, the specific gravity of its solid 

 parts, the quantity of liquids and elastic fluids which it contains 

 in their different states^ and finally what eharcoal furnishes. 



After having exactly dried different specimens of wood in 



2 B 2 



