36 On the Relation of the Specific July 



on the edge of the vessel, and are tightened from above by 

 nuts, so that by interposing between the plate and the edge 

 of the vessel a portion of oil skin, the access of water and 

 external air is completely prevented. This vessel is con- 

 tained in a larger one, also made of brass, intended to hold 

 a determinate quantity of water at the temperature of the 

 atmosphere, in which is placed a small mercurial thermo- 

 meter with a brass scale, and covered bulb, which is com- 

 pletely immersed in water. 



To ascertain the specific heat, the small vessel was filled 

 with the substance in powder, if it was a solid, and the 

 weight noted. The vessel was then closed with the brass 

 plate, and was kept in a vessel full of boiling water, until 

 it was concluded that it, as well as its contents, had acquired 

 all the heat which could be communi<iated to it by boiling 

 water. 



The temperature of the air; that of the water contained 

 in the interior vessel of the apparatus, and that indicated by 

 the thermometer which was plunged into it were marked ; 

 the small vessel was then rapidly removed t from the vessel 

 of boiling water, by means of a pair of pincers, and placed 

 in the exterior vessel. This being done, the temperature 

 indicated by the thermometer of this vessel was marked 

 every minute. This temperature increased at first rapidly, 

 then slowly, and generally reached its maximum in eight 

 or ten minutes. It is obvious that this method would be a 

 very easy one for determining the specific heat of bodies, 

 if it did not happen that during the experiment, the water 

 in the exterior vessel is constantly giving off* heat at the 

 expense of the substance, which is the object of experiment, 

 and conveying it to the vessel and surrounding bodies. 

 Avogrado, however, corrected this source of error by 

 applying Newton's law, according to which, the communi- 

 cation of heat is continually proportional to the actual 

 difference of temperature between the two bodies, a law 

 which is exact for moderate temperatures. He found also 

 a formula nearly accurate, in which the excess of tempera- 

 ture of the exterior vessel, and of the water contained in it, 

 above that of the surrounding air, as well as of the interior 

 vessel, and the substance contained in it above that of the 

 water, is regarded as being a mean during the experiment 

 between the initial and final excess. 



