254 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1910. 



EXPERIMENTS UPON SUBSTANCES OTHER THAN OIL. 



All of the preceding experiments except those recorded in Table I 

 were made with the use of a specially cleaned gas-engine oil of 

 density 0.9041 at 25° C. Those in Table I were made with the use 

 of a similar, though more volatile, mineral oil (machine oil) of den- 

 sity 0.8960. The reason that we worked so continuously upon a single 

 substance was that it was found that in order to maintain a drop of 

 constant size it was necessary, even with these very nonvolatile sub- 

 stances, to have the drop in equilibrium with its saturated vapor. 

 This is shown by the following observations. The inner surfaces 

 of the condenser plates had been covered with a very thin coat of 

 machine oil in order that they might catch dust particles. Drops 

 blown from a considerable number of nonvolatile substances were 

 introduced between the plates and were found in the main to evap- 

 orate too rapidly to make accurate observing possible. This was true 

 even of so nonvolatile substances as glycerine and castor oil, as the 

 following: observations show : 



In order to get rid of this continuous increase in G, the drops were 

 next blown from the least volatile liquid at hand, viz, gas-engine oil, 

 and the behavior of a given drop showed immediately that it was 

 growing in size instead of evaporating. This can be seen from the 

 following readings : 



