238 Royal Society : — 



"On Liquid Transpiration in relation to Chemical Composition." 

 By Thomas Graham, Esq., Y.P.R.S, Master of the Mint. 



In accordance with the analogy of the transpiration of gases, the 

 passage of liquids under pressure through a capillary tuhe is spoken 

 of as liquid transpiration. The subject owes the development which 

 it has already attained chiefly to the investigations of M. Poiseuille. 

 The precision of the mode of experimenting pursued by that phy- 

 sicist has been remarked on by every one who has engaged in the 

 inquiry. The same method was accordingly adopted with little 

 variation in the present investigation. 



The isolated observation made by M. Poiseuille, that alcohol di- 

 luted to different degrees is most retarded in passing through a ca- 

 pillary tube at that degree of dilution where the greatest condensa- 

 tion of the mixed liquids occurs, was understood by the author as 

 indicating that the definite hydrate of alcohol containing six equiva- 

 lents of water (or three equivalents of water with the formula of 

 alcohol taken as C 2 H 3 2 ), was the most retarded in transpiration. 

 The rate of transpiration appeared here to depend upon chemical 

 composition, and to afford an indication of it. A new physical pro- 

 perty may thus become available, like the boiling-point and others, 

 for fixing the chemical constitution of substances. The same feature 

 was recognized in methylic alcohol, although the six-hydrate here is 

 not remarkable for condensation of volume ; and the inquiry was then 

 extended to the hydrated acids, and to other substances. The results 

 appear to establish the existence of a relation between transpirability 

 and composition. 



The time of passage of equal volumes of different liquids under the 

 same pressure and at the same temperature, may be termed their 

 transpiration times, and be referred to the time of water as unity. The 

 transpiration of nitric acid, NH0 6 , with and without water, at 20° C. 

 was as follows : — 



Water added to 100 Transpiration time 



Nitric acid (NH0 6 ). (water =1). 



0-9899 



25'47 1-9885 



28-56 (2 equivalents) 2'0258 



30 2-0459 



40 2-0833 



42*85 (3 equivalents) 2*1034 (the maximum). 



45 2*0977 



50 2*0919 



55 2*0632 



57-12 (4 equivalents) 2*0459 



60 2*0387 



70 1*9626 



80 1*8994 



90 1-8261 



100 1*7040 



200 1-3563 



