100 IS THE GAS CARBONIC ACID? 



power residing in the walls of the vessel ; it only 

 shews the tension of the gas. 



If the walls of the vessel were permeable to the 

 gas under a certain pressure, no further rise, beyond 

 that point, could occur. 



If, in the apparatus, Fig. 4, we push the tube a 

 through the cork down to the little lead drop ; if 

 we then fill the tube c with water to which some 

 yeast has been added, and a with solution of sugar, 

 and expose the whole to a temperature of from 

 68 to 75, the liquid rises in b, from the gas disen- 

 gaged in c, very rapidly, so as to overflow. If c be 

 filled with solution of sugar, and a with yeast, the 

 same rise occurs, and lasts till the disengaged gas 

 puts an end to the contact between the membrane 

 and the liquid. 



It is hardly necessary to point out, that the idea 



above expressed as to the cause of the flow and 



pressure of the spring sap, is nothing more than an 



indication of the direction in which experiments 



must be made. When we know with accuracy the 



volume of the liquid which flows out of a vine at 



the time of flowering, and the quantity of gas 



which is developed at the same time, we shall, I 



trust, find ourselves a step nearer to the explanation 



of this phenomenon. According to the experiments 



The disen- of GEIGER and PROUST, the sap of the vine is rich 



probab?y S1S in carbonic acid ; and it is possible that the gas 



acid. which is disengaged, may be no other than carbonic 



acid gas. 



