:382 



Mr. J. L. Hooo- on Friction in 



to be sure, of little value to give the measurement of a 

 pressure by the gauge where a column of mercury a fraction 

 of a millimetre high requires to be measured, and especially 

 is this true where the tube containing the mercury has been 

 heated and cooled repeatedly. The mercury has a habit of 

 sticking to the glass to such an extent that pressure measure- 

 ments under the conditions mentioned are surely not reliable. 

 The value of the pressure given above, then, only indicates 

 the order of magnitude of the pressure. Though the factor 

 of the gauge used was 95813, yet it was quite inadequate to 

 measure the pressure of the gas in the vessel. 



Removal of Water Vapour and Mercury Vapour from the 

 Hydrogen in the Viscosity Apparatus. 



For this purpose it was necessary to make arrangements 

 by which no vapour should be carried into the apparatus 

 with the entering gas, and also all the vapour which was 

 already in the apparatus might be taken out. The following 

 arrangement was finally adopted (fig. 2). E is a U-tube of 



Fig, 2. 



H 



G 



small bore and bent so that it may enter the long Dewar 

 vessel already mentioned. For reasons which will appear 

 later it was found necessary for the remainder of the investi- 

 gation to replace the tube C (fig. 1) by this tube E. ' is a 



tube leading from the 



generator 



It enters Gr, which is 



