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XIX. On lAgidd Transpiration in relation to Chemical Composition. 
By TnoiLis Geaha3I, Master of the Mint. 
Eeceired June 20, — Bead June 20, 1861. 
The passage of liquids under pressure through a capillary tube is here spoken of as 
liquid transpiration, in accordance with the analogy of gaseous transpiration. The 
subject owes the deyelopment which it has already acquhed chiefly to the investigations 
of the late Dr. Poiseuille *. The precision of the results attainable by the mode of expe- 
rimenting pursued by that physicist has been remarked on by every one who has followed 
him in the inquiry. The observations we owe to M. Poiseuille and other inquirers 
are very numerous, but have not, so far as I am aware, been connected hitherto with 
any speculative ^iews of the chemical or molecular constitution of liquids. 
The isolated discovery of M. Poiseuille, that diluted alcohol has a point of maximum 
retardation, coinciding with the degree of dilution at which the greatest condensation 
of the mixed liquids occurs, appears to offer a starting-point for new inquiries. The 
same result may be othei’wise expressed, by saving that the definite compound of 1 equiv. 
of alcohol with 6 equivs. of water, C4HQ02+6H0f, is more retarded than alcohol 
containing either a greater or a smaller proportion of water. The rate of transpi- 
ration appears here to depend upon chemical composition, and to afford an indication 
of it. A new physical property may thus become available for the determination of 
the chemical constitution of substances. Methylic alcohol being found to exhibit the 
same remarkable feature in its transpiration, although the 6 -hydrate of that alcohol is 
not distinguished by extraordinary condensation of volume, the inquiry was extended 
to the hydrated acids. The results obtained with the latter substances give a certain 
degree of generality to the relation subsisting between the ti-anspirability and chemical 
composition of liquids. 
The apparatus employed was very similar to that of M. Poiseuille. It consisted of 
a small but rather stout glass bulb, A (see figure), about two-thirds of an inch in dia- 
meter, having a capacity of from 4 to 8 cub. cent., blown upon a thick glass tube, with 
a bore of about 2 millimetres. A scratch (c) was made upon the glass tube above, and 
another (d) below the bulb, to indicate the available capacity of the instrument. The 
lower tube was bent at a right angle to the upper, and a fine capillary tube, B, from 3 to 
4 inches in length, was sealed to the curved extremity of the tube. The bulb and capil- 
lary were always held immersed in a vessel of water during the experiment, in order to 
secure uniformity of temperature. The force employed to impel the liquid through the 
* Mem. Savans Strangers, tom. ix. p. 433. 
t Halving the equivalent of alcohol, the hydrate of greatest retardation becomes CgHgO + SHO. 
3 F 2 
