Mitchell on the Penetrativeness of Fluids. 319 



At this period of the experiment, when the mercurial column 

 stood two inches and a halflower, proportionally, than at the com- 

 mencement, a vessel containing carbonic acid gas was placed over 

 the shorter limb. Immediately the long column began to rise 

 fths of an inch in 20 minutes, or 10 minutes per -^th. 

 -Jth more in 10 or 10 per th. 



th in 12 or 12 per th. 



|th in 3?| or 37^ per th. 



-j^th in 60 or 120 per ^th. 



The column appearing stationary, was left nine hours unobserved ; 

 at the end of that time 



l were lost in 9 hours, or 4l min. per ^th. 



^ths in 3 hours 21 minutes, or 40 T 2 ^ min. per-^th. 



^ths in 1 hour 24 minutes, or 42 min. per ^th. 



At this moment the mercury came into contact with the mem- 

 brane, all the gas being excluded. 



The uniformity of descent, and the progressively diminishing rise, 

 are striking facts. It will also be observed, that the carbonic acid 

 seemed to cease action, because of a weight of nearly thirty inches of 

 mercury ; whereas, in another experiment, sixty-three inches were 

 readily driven upwards. We therefore easily perceived the cause of 

 Dutrochet's mistake. 



One other nullifier of endosmose is thought by Dutrochet to exist. 

 A solution of hydro-sulphuret of ammonia at first quickened, and 

 then totally arrested the motion of the fluid in the stem of his 

 endosmometer; for which he accounts by supposing the final pro- 

 duction of sulphuretted hydrogen in the solution, and the extinctive 

 agency of that. 



The great activity of gaseous sulphuretted hydrogen, on which 

 Dutrochet made no experiments, led me to suspect that its solution 

 was gifted with considerable penetrant power, and by thus counter- 

 balancing the amount of penetrating water, appeared to act in arrest 

 of motion, presenting just such a case as we witnessed when com- 

 paring together olefiant gas and arsenuretted hydrogen. For veri- 

 fication, a solution of sulphuretted hydrogen in water was, by means 

 of the inverted syphon, compared with water, and scarcely any 

 motion observed. A similar solution, enclosed by an animal mem- 

 brane in a wide-mouthed bottle, was placed in a vessel of pure 

 water, mouth downwards. In this instance the membrane gave no 

 sign of inflection at first, but after several hours showed a slight 

 bend inwardly. In both these cases the portion of liquid, originally 

 clean water, when tested by acetate of lead, afforded the deep 



