io 4 TRANSPIRATION AND ASCENT OF SAP ch. 



carried out with air-free liquids. As a matter of fact, 

 his method of experiment shows that the water contained 

 air, and he expressly states that the water was, in his first 

 experiments, supersaturated, and that it was only at 

 Regnault's suggestion that he carried out experiments on 

 air-free water. His final conclusion is ' Le phenomene 

 [dilatation of water under tension] se produit done dans 

 le vide aussi bien que dans l'air, et est independant de la 

 sursaturation." 



Cohesion of water containing dissolved air.- 

 Misled by the misquotations just alluded to, although 

 a priori there seemed no reason to suspect that the presence 

 of dissolved air would weaken the tensile strength of water, 

 Dr. Joly and the author considered it necessary to investi- 

 gate the point specially. 



We used a cylindrical glass vessel with rounded ends 

 and provided at one end with a narrow tubulure. This 

 vessel was very carefully cleansed by washing it internally 

 successively with caustic potash solution, dilute acid, and 

 distilled water. Half filled with water it was boiled for 

 some time to make sure that the walls were thoroughly 

 wetted ; then it was almost completely filled with water 

 which had been previously boiled to get rid of undissolved 

 air and to wet thoroughly all dust particles which might 

 have been contained in the liquid. By subsequent 

 exposure, this water was allowed to become saturated 

 with dissolved air. During this care was taken to 

 shield the water from dust, which might not have been 

 completely wetted, or which might have introduced small 

 bubbles. To fill the vessel a small quantity of water in 

 it was raised to ebullition, and, while steam was issuing 

 from the attenuated tubulure, the latter was submerged 

 in the dust-free water. As the steam within condensed, 

 and the vessel cooled, the latter became completely filled 

 with water. A small bubble was then introduced, and the 

 vessel was closed by sealing off the tubulure. 



