PROFESSOR THOMAS GRAHAm's SCIENTIFIC WORK 



189 



tlie name of "transpiration," which lie had previously applied to the 

 similar passage of gases through ca[)illary tubes, he eommunieated 

 his results to the lioyal Society in a paper " On liipiid transpiratiou 

 in relation to chemical composition."* The uiethod he followed in his 

 exi>eriments was precisely that of Dr. Poiseuille, and the principal 

 results at which he arrived are the following: 



1. That dilution with water does not effect upari passu alteration 

 in the transpiratiou velocity of certain liquids ; but that dilution up to a 

 certain point, corresponding to the formation of a definite hydrate, not 

 unfrequently retards the transpiration velocity (or increases the trans- 

 piration time) to a maximum, from which the retardation gradually 

 diminishes with further dilution. This is well seen in the following 

 table, giving the transpiration times of certain liquids in their undi- 

 luted state, and also the maximum transpiration times observed with 

 the same liquids when diluted with a regularly increasing quantity of 

 water, the particular dilution causing the maximum retardation corre- 

 sponding in every case to the production of a definite hydrate : 



Water H^O 



Snlpburic acid . . H 2 S 4 



Nitric acid HNO3 



Acetic acid H 4 C 2 3 



Alcobol Hc.CsO 



Wood-spirit ....H4CO 



Acetone HeCsO 



X Aq. 



HnS04.Aq. 



2HNOs.3 Aq. 



Ii4C2 02.2Aq. 



HnCoO.S Aq. 



H4CO.3 Aq. 



H0C3O.6 Aq. 



2. That the transpiration times of homologous liquids increase reg- 

 ularly with the comi)lexity of tJie several molecules constituting terms 

 of the same series — certain first terms of the different series, however, 

 presenting some anomalies, as was, indeed, to be expected. The trans- 

 piration times of the fatty ethers are given below in illustration. Similar 

 results were obtained with the series of fatty acids and their correspond- 

 ing alcohols: 



Transpiration times. 

 Water H.^ O 1.000 



Ethers. 



f Formic H o C 3 O 2 . 



I Acetic H8C4O.2. 



Ml 



553 



] Butyric H12C0O3 750 



[valeric HnCjOa 827 



In this i:>aper Mr. Graham also recorded the results of two very full 

 series of determinations of the transpiration rates of water at different 

 temperatures between 0° and 70°, and of two similar series of ex- 

 periments made with alcohol. The transpiration velocity of water was 

 found to increase uuiforndy from U.o.jD at 0"^ to l.(M)t> at L'Oo, and thence 



' Philosophical Transactions, 1861, p. 373. 



