RICHARDS AND MATHEWS. 



HEAT OF EVAPORATION. 



535 



mean 539.6 (cal. 21°), essentially the same as the value found by the 

 graphic extrapolation, upon which indeed the values are directly 

 dependent. 



Feeling that it was desirable to test these conclusions in another 

 apparatus, a new vaporizer was made, — unfortunately, however, with 

 a somewhat wider and heavier exit tube. In this apparatus both the 

 warming effect of the vaporizer upon the calorimeter and the loss of 

 heat from premature condensation were greater than before — the 



Heat of Evaporation of Water. 

 Series II, with Vaporizer II. 



former instead of being about 0.009° per minute became about 0.013, 

 and the correction for premature condensation also increasing from 

 7 calories per minute to nearly 9.7 calories per minute. The determi- 

 nations were also somewhat less concordant than before, as was to 

 have been expected on account of the larger correction for radiation 

 and conduction. Nevertheless they add valuable confirmatory evi- 

 dence to the results given in the previous series, and accordingly are 

 recorded in the following table arranged in the same way as those. 

 Experiments 7, 8, 9, 10 and 11 were consecutive, and were made on 

 the 7th and 8th of April, 1908. Experiment 12 was made at another 

 time, but accords satisfactorily with 11, having about the same rate. 

 During Nos. 7, 9 and 10 the barometer stood at 763 millimeters; dur- 

 ing Nos.<8 and 11 at 766 millimeters, and during 12 at 762 millimeters. 



