THE EVAPORATION OF LIQUIDS. 



The principal object of these experiments was to compare the 

 relative rates of evaporation of certain liquids under different 

 conditions of temperature, surface, wind velocity, etc. v Two 

 Babington's atmidometers (A and B) were employed. 



The scale divisions on each instrument were carefully calib- 

 rated, and the following constants determined : 



A, 15.4 grams per division; B, 25.3 grams per division. 



That is to say, it required these masses to be placed in the 

 upper pan to depress each stem through one scale division. It 

 is obvious therefore that the total evaporation in the pan of A 

 which would cause a rise of one division, would be equivalent to 

 15.4 grams. 



The pans used had slightly different diameters, so that the 

 surface areas exposed were as follows: A, 7.1 sq cm., B, 6.2 

 sq. cm. 



The observations were made by filling the pans with the liquid 

 to be tested, then focusing the cross wire of a telescope on a 

 certain division on the scale, and noting the rise due to evapora- 

 tion in given intervals. That the evaporation rates were fairly 

 constant is shown by the figures in Table I which give an idea 

 of the nature and results of the experiments with ether .and 

 alcohol. The time interval was five minutes, and there are 

 recorded the corresponding scale readings, the rise due to 

 evaporation and the equivalent in grams for each liquid. Both 

 these sets of observations were made simultaneously. When 

 the surface of B is reduced to the same dimensions as that of 

 A it is seen that ether evaporates nearly ten times as rapidly as 

 alcohol. 



In Table 24 the conclusions of a series of observations similar 

 to those in Table 23 are given. The temperature, pressure, and 

 relative humidity were kept fairly constant. Expressing these 

 results relatively, water being taken as unity, we have the follow- 

 ing: Water, i.o; alcohol, 3.2; carbon bisulphide, 8.8; ether, 

 28.8; chloroform, 40.0. 



In Table 25 a comparison is made of the relation of evapora- 

 tion to the extent of surface. If we multiply the evaporation of 

 A by the surface of B it should equal the evaporation of B multi- 

 plied by the surface of A. Our result gives 0.248 and 0.247, 



40 



