Liquids in contact with Different Gases. 405 



if we assume that the liquid in the manometer is identical 

 with that under investigation. It follows, therefore, that hi 

 is the height to which the liquid would rise in a capillary 

 tube of radius r if its contact-angle happened to be zero. 

 But if the liquid has a contact-angle 0, the height measured 

 in the Jaeger experiment is greater than the height measured 

 in the corresponding capillary-tube experiment in the pro- 

 portion 1/cos 6. (This fact might be made the basis of a 

 method for the measurement of contact-angles.) 



Moreover, we see from equation (i.), still assuming h' to 

 be zero, that very approximately 



2a?p / =rp 1 h 1 ; 



so that, if h be the height to which the liquid would rise in a 

 capillary tube of the same radius, we have, assuming the 

 liquid to have a zero contact-angle, 



Pi 



Thus, if a liquid of very low density be used in the mano- 

 meter, it is easy to arrange matters so that h l , the maximum 

 height observed in the Jaeger experiment, shall be from 10 

 to 20 per cent, higher than the value of h observed in the 

 corresponding capillary-rise experiment, and corresponding- 

 small variations can therefore be more easily traced. 



In the experiments detailed below a water-manometer was 

 used, as the variations observed were well within its range, 

 and the change of density of water with temperature is very 

 exactly known. 



Carbon dioxide and air were the o-ases chosen for in- 



o 



vestigation, and experiments have been made on benzene, 

 turpentine, water, methyl and ethyl alcohols, chloroform, 

 and ether. 



The experimental arrangements were quite simple. A 

 Y-tube of glass was titled with two stop-cocks on the bent 

 limbs of the Y« One of the limbs was connected through a 

 <lry:ng-tube filled with fragments of calcium chloride to a 

 Boyle's bottle, which supplied a steadj r current of air, the 

 other limb being similarly connected through a second 

 drying-tube to a Kipp's apparatus for generating carbon 

 dioxide. Iu order to steady the flow- of the carbon dioxide 

 it was found necessary to insert, between the generator and 

 the drying-tube, about two feet of fine capillary tubing. 

 With this arrangement it was possible, by regulating the 

 stop-cocks, to obtain a slow delivery of the gas, about one 



