306 report— 1859. 



able to bring forward the results of some experiments on this very interesting 

 branch of the subject. 



Capillary Ascension and Diffusion of Saline Solutions. — The experiments 

 of Valson, Poiseuille, and Willibald Schmidt, indicate that the capillary height 

 of fluids and the rapidity of their flow through capillary tubes is not alto- 

 gether dependent upon their density, but is also influenced by the nature of 

 the substances in solution. Valson * has examined the influence which the 

 addition of one fluid would have upon the capillary height of another. He 

 finds that this would be different according as the intervening fluid acted 

 chemically or not upon the other; in the latter case only did the capillary 

 height appear as a linear function of the increment of volume, while both 

 those magnitudes may be expressed by an exponential curve with asymptotes 

 when chemical action takes place. He has deduced the following results 

 from experiments made with sulphuric acid (HO, S0 3 ), concentrated acetic 

 acid, and alcohol, by the successive addition of increments of water to them : 

 — 1, that a change of capillary height takes place regularly as each success- 

 ive increment of water is added ; 2, the action of the successive increments 

 upon the capillary height diminishes; 3, a modification of molecular activity 

 exerts a greater influence on the capillary height than an alteration of 

 specific gravity of the fluid mass; 4, the mixture of the bodies above named, 

 although capable of being made in every proportion, may nevertheless be 

 considered to belong to the category of chemical combination. Valson found 

 that the addition of about l u * of alcohol to water produced an alteration 

 of 0*2 millim. in a capillary column of 41 48 millims., which was very well 

 determinable by the cathetometer. 



The experiments of Poiseuille to which I refer, are those upon the flow of 

 liquids through capillary tubes t. From those made with water and alcohol, 

 he infers that the velocity of the flow is directly proportional to the pressure, 

 and inversely to the length of the tube, provided that this length does not 

 fall below a certain limit which increases and diminishes with the diameter; 

 for shorter tubes he found that the velocity increases more rapidly than the 

 pressure. He found further that, all other conditions being the same, the 

 quantity discharged is proportional to the fourth power of the diameter of 

 the tube. The addition of substances soluble in water modified, however, the 

 velocity of flow ; iodide, bromide, and cyanide of potassium, nitrate of potash, 

 nitrate of ammonia, chlorides of ammonium and calcium, and acetate of 

 ammonia accelerated it, while bases retarded it. Among the acids only two 

 appear to have accelerated it, — hydrocyanic and hydrosulphuric acids. He 

 only obtained negative results from his further researches to determine how 

 far the alteration, produced by the addition of various substances, in the 

 density, capillary height, liquidity, boiling-point, contraction on mixture, 

 solubility and efflorescence of the substances added, See., stood in any simple 

 relation to the modification in the rate of flow. The experiments of 

 Schmidt + on the influence of temperature on the rapidity of filtration, 

 confirm in the main Poiseuille's results just given. 



I propose to use both the capillary height as determined by the catheto- 

 meter, and the flow of the solutions through capillary tubes, as tests of the 

 molecular changes which take place in solutions of a single salt at different 

 temperatures, and with mixtures of salts according to the schemes laid down 

 above. The instrument which I am constructing for the experiments on the 

 flow of the solutions consists of a modification of Vierordt's endosmometer, by 

 which I can use tubular diaphragms of various lengths and diameters of tubes, 



* Compt. Rend. vol. xlv. p. 101. t Ann. de China, et de Phys. vol. xxi. p. 76. 



X Poggendorft's Annalen, vol. xcix. p. 353. 



