292 



HISTORY OF SCIENCE. 



The method of estimating specific heats by the quantity of ice which 

 a body is able to melt in parting with its excess of temperature above 

 the freezing-point has been much employed, Laplace and the cele- 

 brated French chemist, Lavoisier (whose chief scientific work will be dis- 

 cussed in a subsequent chapter), devised an apparatus in which Black's 

 method was used, modified by the circumstance that large blocks of 

 pure ice such as those used by Black could not be easily obtained in 

 many localities. Fig. 139 represents this apparatus, which Lavoisier, 

 with more regard to convenient distinction than to etymological ele- 

 gance, called the Calorimeter. The substance the specific heat of which 



is to be determined is con- 

 tained in a kind of cylindri- 

 cal cage formed of iron wire, 

 F F, and surrounded by small 

 pieces of ice contained in a 

 middle cavity, dd, from which 

 at the end of the experiment 

 the water is drawn off at x 

 into a suitable vessel, and 

 weighed. The ice contained 

 in ddis shielded from receiv- 

 ing external heat by means of 

 an outer cylindrical cavity a a, 

 which is filled with pounded 

 ice. The water produced by 

 the melting of the ice in a a 

 is allowed to drain off at x. 

 There is also a lid, B B, con- 

 taining a stratum of pounded 

 ice. Thus in an apartment 

 where the air is not below but 

 a little above the freezing- 

 FIG. 139. point, experiments may be 



conducted with this apparatus 



without the internal cavity receiving any heat from without. When a 

 liquid is the subject of experiment it is enclosed in a glass or other 

 vessel, the specific heat of which has been previously ascertained, in 

 order that from the quantity of water collected the amount due to the 

 containing vessel may be deducted. To determine the quantity of 

 heat disengaged during combustion or other chemical action, the bodies 

 are. burnt or combined in the interior cavity after their temperature 

 has been reduced to 32. The apparatus also admits of estimates 

 being made of animal heat produced by respiration. For this last kind 

 of experiment a guinea-pig, an animal which does not suffer from the 

 cold, is introduced into the interior cavity, and supplied with air cooled 

 to 32 by means of one pipe, while another pipe carried spirally through 



