RICHARDS AND MATUEWS. — HEAT OF EVAPORATION. 513 



would be exactly counterbalanced by tbe loss in the second half. Tliis 

 practice has recently been found to be of very doubtful advantage.* In 

 Lsis Ure^ found the value 037.5 calories; and Despretz,"'' in 1823, 

 published the value 03 1 as the result of one series of measurements, 

 and 040 as the result of a second series, his apparatus having been 

 similar to that used by Rumford. The next work was done by Brix ^ 

 in 1842, who pointed out many of the causes of error and sought to 

 correct them mathematically. Ilis value for water was 040, including 

 the heat given up by the water between 100° and 0°, — a result very 

 close to the most probable figure. 



In 1847 Regnault^ published his exhaustive memoir upon this sub- 

 ject, which surpassed in detailed precautiofi any preceding work. As 

 an average of thirty-eight separate determinations he obtained the 

 value 030.07 calories, the individual values varying between 035.0 

 and 038.4. 



The work of Andrews ^° may be considered somewhat more in detail, 

 because his method was similar to those which have since been usually 

 employed. He distilled the liquid fi-om a screened retort into a spiral 

 condenser placed in a calorimeter, and noted the rise in temperature. 

 The water equivalent of his calorimeter, water, and utensils was only 

 about 280 grams, the amount of water distilled was a little less than 

 two grams, and there was no device to prevent particles of water from 

 being carried over in the vapor, so that the method was still evidently 

 in its infancy. His thermometric precautions and his efforts to apply 

 corrections for heat lost and gained by radiation were very crude, as 

 was also his method for determining specific heats ; but nevertheless, 

 for alcohol, he obtained 202.4 at the boiling point, a value which is but 

 three per cent lower than the present accepted value. His two figures 

 for water, 531 and 543 calories (not including the heat required to 

 warm the water), obtained at different rates, were less satisfactory ; 

 premature condensation evidently took place in his apparatus. 



Favre and Silbermann ^^ shortly afterwards measured the heats of 

 vaporization of a number of organic liquids as well as of water, but the 

 amount of material used was very small and the method in general un- 

 satisfactory, so that their results are of but doubtful value. 



" T. W. Richards and L. L. Burgess, J. Am. Chem. Soc, 32, 449 (1910). 



6 Ure, Phil. Trans., 1818, p. 385. 



T Despretz, Ann. Chim. Phys., (2) 24, 323 (1823). 



8 Brix, Pogg. Ann., 56, 341 (1842). 



9 Regnault, M<^m. de I'Inst. de France, 21, 638. 

 " Andrews, Pogg. Ann., 75, 501 (1848). 



" Favre and Silbermann, Ann. Chim. Phys. (3) 37, 461 (1853). 



VOL. XLVI. — 33 



