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IX. On the Microrheometer. 
By J. R Hannay, F.R.S.E., F.C.S., lately Assistant Lecturer on Chemistry in the 
Owens College, Manchester. 
Communicated by H. E. Roscoe, Ph.D., Professor of Chemistry in Owens College, 
Manchester. 
Received December 11, 1878,—Read January 23, 1879. 
[Plate 35.] 
The examination of the phenomena of the flow of liquids through capillary tubes, as 
well as the discovery of the fact that chemical composition influenced the rate of flow, 
were the work of M. Poiseitjlle,* who, in the paper referred to, gave the results of an 
extended series of carefully conducted experiments, illustrating the laws regulating 
the rate of flow as affected by the length and diameter of the tube, the pressure acting 
upon the liquid, and also, within a certain range, by the temperature. His work 
was carefully examined, in an experimental manner, by a commission of chemists and 
physicists, and found to be very exact. The formula for the rate of flow which he 
found was— 
HD 4 
Q= 1836724(1 + 0-0336793I + 0-0002209936T') 
where— 
Q = quantity of liquid passed. 
T = temperature in centigrade degrees. 
H = pressure on liquid, measured by mercury column. 
D = diameter of tube. 
L = length of tube. 
Poiseiulle pointed out that these results are different from those obtained by 
other investigators, but the results of others had been obtained by using tubes of 
much greater diameter, so that the laws regulating the flow of liquids through capil¬ 
lary tubes are different from those relating to wide tubes. The most characteristic 
law relating to capillary tubes appears to be that the rate of flow varies directly as the 
pressure; and as it is also the readiest method of testing a tube, I shall only use the 
* “ Recliercbes Experimentales sur le Mouvement des Liquids dans les Tubes de tres-petits Diametres,” 
‘ Annales de Chimie et de Physique ’ [3], t. vii., p. 50. 
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