348 



quick line. Tlie vessel P is cleaned, care- 

 fully dried, and if possible several times washed 

 out with the vapours of the boiling liquid T^; 

 then it is filled again with a fresh quantity 

 of the liquid F, while a layer of dry mercury 

 is poured into W. The tube is placed into the 

 oil thermostat, and the capillary tube with 

 the part GBC tlxed to it, is lowered then, 

 till G makes contact with the surface of the 

 mercury. If V has reached a constant tempe- 

 rature, the capillary tube is further lowered 

 by screwing it so far downwards, as is necessary 

 to bring it just in contact with the surface 

 of the liquid. This enclosure by means of mer- 

 cury insures a sufficient freedom of motion, 

 while the liquid at the same time can be shut 

 otf from the air ^), and the small bubbles of 

 nitrogen, emerging from k, can freely escape 

 at C and Z^. All communications with the free 

 atmosphere, which are present in the connect- 

 Fig. 7. ing tubes of fig. 1, are provided with drying 



apparatus, filled with dry calcium-oxide. 



§ 13. All measurements now were made in such a way, that 

 always the zero-point was controlled anew accurately, before and 

 immediately after each reading of the manometer. One needs to 

 ascertain first, that all connecting tubes (fig. 6) are free from 

 leakage, and that a diminution of the speed of gas-flow has no 

 influence any longer on the value of the maximum pressure H. 

 After the highest point of the octane-column is reached the liquid 

 falls suddenly back to a point, which depends upon the speed of 

 gas-flow, and then it begins to rise again slowly ; etc. By experience 

 one learns to estimate the reliability of the measurements, by the 

 particular motion of the octane in the manometer ; finally the repro- 

 ducibility of the \alue of H needs to be considered as the decisive 

 criterion for answering the question, if the i-eal pressure of equili- 

 brium in the gas-bubble has been measured. Even when the speed 

 of gas-flow is varied within certain limits, this value appears to be 

 reproducible quite exactly. The influence of the variation of the 

 depth of immersion i on the manometer-readings, can be found by 



1) For if necessary, the air in the vessel P can be first substituted by a current 

 of pure nitrogen. 



