460 Messrs. C. H. Bosanquet and H. Hartley: Notes 



shallow rectangular plate-glass trough into which the liquid 

 under investigation was poured to a depth of 2 or 3 mm. 

 The trough was then tilted until the liquid in it formed a 

 prism with an angle of about 5°. The trough was supported 

 about a foot above a table on which was a sheet of white 

 paper with a line drawn parallel to the refracting edge of the 

 liquid prism. The line was observed through the liquid 

 from a point about two feet above the trough, the effective 

 diameter of the pupil of the eye being cut down by means of 

 a tinfoil screen with a small pinhole in the centre. If the 

 angle of contact is finite, there should be an area above the 

 liquid in which the line is invisible. This method would 

 probably detect an angle of contact as small as 30'. Xo 

 disappearance of the dine was observed with any of the 

 liquids used, and the surface of the liquid near the line of 

 contact with the glass was always definitely concave, the 

 concavity being shown by the apparent narrowing of the 

 line. 



Before each observation the liquid was run over the whole 

 surface of the bottom of the trough, and ten minutes were 

 allowed for draining. In the case of turpentine, it was 

 noticed that the liquid which drained off the exposed portion 

 of the bottom of the trough did not unite completely with 

 the bulk of the liquid, but formed a ridge at the boundary 

 of the liquid. The surface in passing from the bulk of the 

 liquid to the glass was first concave, then convex, and finally 

 concave, the surface being tangential to the glass. 



As these experiments were purely qualitative, the liquids, 

 with the exception of the water, were not specially purified. 



Determination of the Angle of Contact between Azobenzene 

 and Water. 



Liquids which wetted glass having all given zero contact 

 angles, a search was made for an organic substance with 

 which water gives a finite acute angle of contact. 



Salol, dinitrobenzene, azobenzene, and triphenyl methane 

 were investigated by fusing small quantities on microscope- 

 slides, allowing them to solidify, and examining the curva- 

 ture of the surface of water in contact with these films. 

 Azobenzene was found to oiye a finite acute angle of 

 contact. 



Plates of azobenzene were then prepared by pouring the 

 fused substance on to mica which was supported by a sheet 



