206 Mr. W. B. Hardy on 



acids with OH and CO OH groups. This conjunction pro- 

 duces a remarkable increase in the lubricating power of 

 a chain compound (a. lactic acid and ricinolic acid), and 

 almost destroys lubricating action in the case of the ring- 

 compounds (salicylic and benzylic acids). 



It will be noticed tbat no ring compound is a good 

 lubricant. Even cholesterol with the molecular weight 366 

 is no exception. 



The group SH acts much as OH, tbiophenol C 6 H 5 OH 

 and benzylbydrosulphide C6H 5 .CH 2 SH resembling phenol 

 and benzyl alcohol respectively. 



It need hardly be stated that these conclusions are pre- 

 sented not as generalizations, but as a summary of the 

 relations which actually obtain amongst the limited number 

 of compounds studied. The fact that the influence of 

 chemical constitution differs widely in degree if not in kind 

 when glass is lubricated would alone enforce caution. 



Mixtures of lubricants were not specially studied, but 

 it is certain that th^y will reveal complex relations of 

 great practical importance. In the experiments solids were 

 deposited in thin layers on the plate from very weak 

 solutions in ether, ethyl alcohol, or bonzene. In most cases 

 the change in friction was followed whilst the solutions were 

 drying and nothing abnormal noted, the friction changing 

 rapidly to the value for the solid in the last stage of drying, 

 and in such a way as to suggest that the combined effect of 

 the two substances was merely additive. In some cases, 

 however, e. g. phenol and cetyl alcohol, abnormal values 

 were noted. J nst before drying was complete the friction fell 

 to a comparatively low level ("07 cetyl alcohol, "15 phenol). 



The values for paraffins can be considered only as 

 approximate. Octane was the purest specimen employed. 

 The solid paraffins were identified by their melting-points 

 and w T ere not wholly free from unsaturated substances, but 

 the displacement of the observed frictions due to this may 

 be considered as being small. 



The lower members of the fatty acid series etched the 

 surfaces so as to expose the crystals, the action being slow 

 and slight in the case of valeric acid. Capryllic acid did 

 not etch the surface. This action no doubt contributed to 

 the bending downwards of the first part of the curve. 



I am indebted to Professor Lapuorth for examples of 

 cyclic compounds, to Sir George Beilby, Mr. Dootson, and 

 Dr. Ida Maclean for various specimens, and especially to 

 Sir William Pope for permission to raid his large collection 

 of substances. 



