338 Mr. T. Tate's Experimental Researches on the 



On the Amount of Vapour absorbed at different Temperatures. 



6. The weight of vapour absorbed by an absorbent in a given 

 time from an atmosphere charged with watery vapour is propor- 

 tional to the tension of the vapour. 



Experiment VII. A jar (J), 5 inches section, containing strong 

 sulphuric acid, was covered with a plate 

 P, having a portion cut out, of the same 

 section as the interior of the jar; a 

 damp cloth was laid on this plate, and 

 the whole was covered by a large re- 

 ceiver (R) standing on a tray contain- 

 ing water. After remaining for twelve 

 hours at a uniform temperature, the 

 augmentation of weight of the jar and ; 

 acid was ascertained, which gave the 

 weight of the vapour absorbed by the 



acid in that time at the observed temperature. The following 

 Table gives the augmentations of weight corresponding to dif- 

 ferent temperatures, other things being the same. 



1 Corresponding 

 Temperature, in weight of vapour 

 degrees Cent., j absorbed, in 

 T. grains, 

 w. 



Corresponding 



tension of 



vapour at T, 



P- 



Value of w by 

 formula 

 w=38p. 



65 

 75 



12-5 

 13-3 

 180 



10-4 

 11-2 

 16-2 

 17-4 

 24-8 



•284 

 •304 

 •423 

 •447 

 •603 



1078 

 11-54 

 1606 

 1700 

 24-90 



The near coincidence of the results given in the second and 

 fourth columns shows that the weight of vapour absorbed by the 

 acid, in a given time, is nearly proportional to the tension of the 

 vapour at the given temperature. 



At first sight it may seem that the amount of vapour here 

 diffused is very small ; but if we convert the weight of water 

 absorbed into watery vapour at the given temperature, we 

 shall find that the volume of vapour is really something consider- 

 able. Thus we find that ] grain of water at 12 0, 5 produces 

 about 450 cubic inches of vapour, so that the volume of va- 

 pour, at this temperature, diffused per hour, from a unit of 

 surface through a unit of distance, would be about 120 cubic 

 inches. 



7. In like manner, it was found that a dry clean woollen 

 cloth, placed in an atmosphere saturated with watery vapour, 

 absorbed in equal times a weight of moisture proportional to 



