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XXX. Intelligence and Miscellaneous Articles. 



ON THE PASSAGE OF GASES THROUGH COLLOID MEMBRANES OF 

 VEGETABLE ORIGIN. BY A. BARTHELEMY. 



H^HE purpose of these experiments was to prove that those of 

 -*- Graham on the dialysis of gases through caoutchouc could be 

 verified on natural vegetable colloid films, and principally on the 

 cuticular surfaces of the leaf, and thus to justify the important 

 part which I make the cuticle play in the absorption of carbonic 

 acid by plants. 



Every body knows the BegoniaceaD with leaves spotted with white, 

 which are cultivated in greenhouses, and the white spots of which 

 are, as I have convinced myself, only elevations of the epiderm 

 upon a layer of nitrogen. The leaves of certain varieties, very thin 

 on the living plant, are reduced, on fading during the winter in 

 darkness, to the condition of a pellicle endued with elasticity and 

 representing almost nothing but the cuticular layers. It was these 

 colloid membranes which served me in repeating Graham's experi- 

 ment. I followed strictly the course of the illustrious physicist, 

 save a few modifications of detail. 



One commences by ascertaining that the membrane is intact, 

 presenting no rents, by the dialysis of air alone. Three experi- 

 ments, made on the 16th, 17th, and 18fch of March, gave the fol- 

 lowing results at the end of six hours : — 



March 16. March 17. March 18. 



Volume of gas collected 5'2 cub. cent. 5*5 cub. cent. 7*0 cub. cent. 

 Volume of oxygen ab-1 



sorbed by pyrogallate > I'd „ 2d „ 2-2 „ 



of potass J 



Proportion of oxygen . . 36 per cent. 41 per cent. 31 per cent. 



Although the proportions of oxygen present a rather wide devia- 

 tion, due to the difficulty of repeating the experiments under the 

 same conditions of external pressure, temperature, and, especially, 

 of hygrometric condition, it may be concluded that oxygen passes 

 more rapidly than nitrogen, and that air thus dialyzed contains on 

 the average 36 per cent, of oxygen. This number is a little below 

 that found by Graham with caoutchouc. 



Having made this verification and obtained this important result, 

 I proceeded to the comparison of the velocities of the three gases 

 which most interest us. For this purpose, having set up a current 

 of carbonic acid above the membrane, I noted the point to which 

 the mercury had descended at the expiration of an hour; then, 

 passing nitrogen or oxygen, I noted the time taken by the mercury 

 to descend to the same level. 



In four experiments, with different membranes, I obtained the 

 following results : — 



1st exp. 2nd exp. 3rd exp. 4th exp. 



Carbonic acid .... 1 hour 1 hour 1 hour 1 hour 



Nitrogen 15 „ 13 h 40 m 15 h 30 m 14 „ 



Oxygen . . 6 „ 6 h 20 m 7 l1 5 h 4(T 



