320 Mitchell on the Penetrativeness of Fluids. 



black precipitate, indicative of the presence, abundantly, of sul- 

 phuretted hydrogen. 



In a second experiment, with a solution of sulphuretted hydrogen 

 enclosed in a bottle, the water placed in the outer vessel contained 

 the slightest trace of acetate of lead. Scarcely was the bottle im- 

 mersed before the precipitation of the lead commenced. Finally, a 

 solution of sulphuretted hydrogen in water was, by means of the in- 

 verted syphon, compared with alcohol confined in its shorter limb. 

 In this instance, and in every repetition, the movement was mani- 

 fested towards the alcohol, the rise of which showed that the pene- 

 trative power of liquid sulphuretted hydrogen is somewhat greater 

 than that of water, and of course much greater than that of alcohol. 

 These experiments were made with extraordinary care, because by 

 them seemed to hang the fate of this whole question of principle. 

 The whole doctrine of regular rate of penetration, &c, must fall to 

 the ground if my trials had been confirmatory of the observations of 

 M. Dutrochet, 



The totally different results, as to the force of penetration, at 

 which M. Dutrochet and myself have arrived, render necessary a 

 few words of explanation. 



It will be conceded that the fairest mode of estimating the force is 

 when the liquid is fresh and the process just well begun. The alti- 

 tude of the highest column of mercury which it can raise will repre- 

 sent its power, and that column should, if possible, be laid on it at 

 once. In this manner I proceeded, and found that both bladder 

 and gum elastic were broken by a column higher than sixty-three 

 inches, although, just before giving way, the column was rising. It 

 could rise solely by the power of penetration, no other known agent 

 of motion being present. But M. Dutrochet, laying on a column 

 less than sufficient, left his apparatus to raise that column for a day 

 or two, until the process of elevation ceased. The height then 

 reached he considered as representing the power of endosmose. The. 

 attentive reader will readily perceive, in this plausible experiment, 

 the same error which deprived the facts, as to time, of value. The 

 solution had become diluted, and the water on the other side had 

 become impregnated, and, independently in a great measure of the 

 weight of the column, the causes of production of penetrating cur- 

 rents had ceased, and these beautiful experiments reported, not the 

 weight which could be raised, but the time required by such a solu- 

 tion to distribute its qualities uniformly, or nearly so, on both sides 

 of the membrane Left in that state the column descends, thus 

 evincing the cessation of penetration, not its forcible repression. 



