188 THE EAKL OF BERKELEY, ME. E. G. J. HARTLEY AND DR. C. V. BURTON: 



This seems to show conclusively that some of the previous gains in weight were due 

 to mercury vapour. 



As the gain at C. (see p. 187) was only 0'0003 gr. for 116 hours' run, it was 

 decided to use this form of vessel (i.e., mercury cups) for work at C., and to reserve 

 the platinum-iridium U -tubes for work at 30 C. 



Test of Fall of Air Pressure. 



In connection with the change of weight in the 2nd solution vessel it was thought 

 possible that the loss might be due to a difference of pressure in the air current, caused 

 by " wire-drawing " the air when passing over and through the platinum rolls. 



The total difference in the pressure of the air when entering and when leaving the 

 train of vessels at a rate of 50 bubbles in 11 seconds was determined and was found to 

 be about 1 mm. of water. This number, even if the whole difference of pressure were 

 supposed to take place between the two solution vessels, is inadequate to account for 

 the loss of weight observed. 



Text to tee whether the Oscillation of the Vessels causes any Change. 



It was thought that the oscillation of the train of vessels might affect the results; 

 for J. J. THOMSON and others have pointed out that the surface layer of a solution is 

 at a different concentration to that of the bulk of the liquid. Now, in the method of 

 operation adopted, the air is caused to pass over platinum rolls recently wetted by 

 the solution, and from which the solution is slowly draining off. It might be that a 

 layer of solution thus left in contact with the air has a different concentration to that 

 of the ordinary surface,* arid this effect was looked for by setting up a vapour-pressure 

 experiment without oscillating the apparatus nor using the platinum rolls, but passing 

 the air over at a slower rate. No appreciable difference resulted (see experiment 

 marked * on next page). 



In the following table all vapour-pressure results with Ca 2 Fe(CN) 6 solutions are 

 given. 



The 1st column gives the date of the beginning of the experiment; the 2nd gives 

 the weight concentration of the solution used, i.e., the number of grammes of 

 anhydrous salt to 100 grammes of water, and is calculated from the analyses given in 

 the table on p. 191, column 3 ; the 3rd gives the mean temperature of the bath ; the 

 4th gives the number of hours the air was passing ; the 5th gives the rate of bubbling, 

 i.e., the time taken for 50 bubbles to pass ; the 6th, 7th, 8th and 9th give the changes 

 in weight in the several vessels. It is to be noted that the algebraic sum of the 



* Another disturbing factor is that the small radius of curvature of the surface of the solution clinging 

 to the thin edges of the platinum rolls raises the vapour pressure ; the experiment without the platinum 

 rolls shows that the joint influence of this together with that indicated in the text is of no practical 

 importance. 



