1879.] Mr. J. B. Hannay. On the Microrheometer. 279 



III. The change of rotation of a solntion of lactin can be expressed 

 by a mathematical equation. 



IY. When the specific rotation 64°*8 is reached, the law of change 

 must be expressed by a different equation. 



V. The initial solubility of lactin is 1 part lactin in 1064 parts 

 water. 



VI. The permanent solubility is 1 part lactin in 3 '23 parts water. 



IV. "On the Microrheometer." By J. B. HANNAY, F.K.S.E., 

 F.C.S., lately Assistant Lecturer on Chemistry in the Owens 

 College, Manchester. Communicated by H. E. RoscOE, 

 LL.D., F.R.S., Professor of Chemistry in the Owens Col- 

 lege, Manchester. Received December 11, 1878. 



(Abstract.) 



In this paper the author reviews the work done by chemists and 

 physicists in determining the relation between the chemical composi- 

 tion of a liquid and its rate of flow through a capillary tube. Poiseuille * 

 ascertained, in a very accurate manner, all the physical laws relating 

 to the rate of flow, as regulated by temperature, pressure, and dimen- 

 sions of the tube ; but on examining saline solutions he could make 

 nothing of the numbers presented, because he used percentage solutions 

 instead of solutions proportional to the equivalent of the body dissolved. 

 Graham,f noticing that Poiseuille had discovered a hydrate of alcohol 

 by running various mixtures of alcohol and water through the tube, 

 examined mixtures of the various acids with water, and found that the 

 hydration proceeded by distinct steps of multiple proportions. Several 

 others, notably Guerout,^ have since worked on the same subject, but 

 as they have only worked on organic liquids, and have done all the 

 rates at the same temperature, the results throw no light on the phe- 

 nomena. Thus water runs about five times as quickly at 100° as at 

 0° ; and in a series of alcohols, such as Guerout experimented upon, 

 the differences between their boiling points were very great, so that, 

 their vapour tensions or molecular mobilities being quite incomparable 

 while at the same temperature, the experiments do not admit of any 

 real interpretation. The author reserves the organic part of the in- 

 vestigation, which requires the determination of vapour tensions, till 

 a future paper, and in the present deals with saline solutions. 



The phenomenon of the flow of liquids through capillary tubes has 



* "Ann. de Chim. et de Physique," [3], t. vii, 50. 

 f "Phil. Trans.," 1861, p. 373. 



X " Comptes rendus," lxxix, p. 1201 ; lxxxi, p. 1025. 



