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PROCEEDINGS OF THE AMERICAN ACADEMY- 



made in the form of a frustum of a cone, the space between the asbes- 

 tos and the glass being closely packed with cotton, and the outside of 

 the cone covered with bright tin foil to cut down the radiation. In 

 order to place the vaporizer as low as possible and at the same time to 

 prevent its becoming wetted, a shallow glass cup was placed immedi- 

 ately below the asbestos shield. The cup also served to prevent loss 

 of heat by evaporation of the calorimeter water at its surface, or by 

 evaporation of water rising on the vaporizer stem by capillary action 

 or other cause, such evaporation being caused by the presence of the 

 hot tube carrying the vapor. In this manner the distance between the 

 boiling liquid within the vaporizer and the calorimeter water was re- 

 duced to a little less than one centimeter. 



In spite of the precautions to prevent radiation, the correction for 

 heat gained by the calorimeter due to this cause was increased from 

 about 0.002° to 0.008° per minute, a quantity which was very carefully 

 determined and applied to the results. 



This vaporizer yielded results which gave when plotted a line less 

 steep than the previous one. The modification had evidently improved 

 the results, but had not wholly eliminated the cause or causes of error. 



In the space above a boiling liquid in a flask, a mist can often be ob- 

 served. This mist is caused by radiation of heat from the walls of the 

 vessel ; and the question arose as to whether the difficulty in obtaining 

 uniform results at various speeds might not be due in part to the for- 

 mation of such a mist within the vaporizer. The mist would not be 

 entirely caught by the trap, and would thus introduce minute drops of 

 water into the condenser, possibly proportional in amount to the time 

 required for distillation. 



In order to discover whether any difficulty arose from this cause, the 

 vaporizer, above the asbestos cone, was surrounded by a jacket through 

 which live steam was passed throughout the measurement. This must 

 have prevented the formation of a mist within the vaporizer ; but the 

 results were no better. 



The ejection of fine drops from the surface of the boiling liquid — 

 drops which might be swept along by the current of vapor — could not 

 have been the cause of the particular trouble in question. Such an 

 action would seem more likely when the boiling is rapid than when it 

 is slow, an outcome exactly the opposite to that actually observed. 

 Doubtless such an ejection occurs to a slight extent, but in our trap 

 its effect had undoubtedly been much reduced. As will be seen, our 

 final result shows that we have been at least as fortunate as others in 

 eliminating this danger. 



Marker, in his desperation on account of obvious premature conden- 



