Chemistry and Physics. 75 



the earlier English translations of the work were made in a very 

 satisfactory way by Dr. Edgar F. Smith of the University of 

 Pennsylvania. 



At present the work appears in two volumes, the first of which 

 deals with the aliphatic compounds. The recent German edi- 

 tions have been prepared under the direction of Dr. Richard 

 Anschutz of Bonn. h. l. w. 



5. Friction and Lubrication. — In discussing lubrication two 

 cases are to be distinguished : (1) When two surfaces are floated 

 apart by a lubricant, static friction is absent and the resistance to 

 motion varies directly as the viscosity of the lubricant. ( 2 ) Where 

 two solid surfaces are near enough together so that the friction 

 depends not only upon the lubricant but also upon the chemical 

 nature of the surfaces, the resistance varies as some inverse func- 

 tion of the viscosity of the lubricant. This second case is termed 

 boundary lubrication. It has recently been studied by Hardy 

 and Doubled ay using polished surfaces of steel, glass, and bis- 

 muth lubricated with liquids of the paraffine series. To assure 

 definiteness of contact area, one of the surfaces was made of 

 spherical form, and the other a plane. The coefficients of friction 

 were first determined for the "clean" state where all possibly 

 removable impurities had been abstracted. This is to be judged 

 from the fact that the friction has a high and constant value. 



The variables studied were (a) the weight of the slider, (b) the 

 curvature, (c) the thickness of the layer of the lubricant, (d) the 

 chemical nature of the lubricant and the solids respectively. The 

 authors find that the friction is strictly proportional to the weight 

 or that the coefficient of friction is (a) independent of the weight 

 and (b) of the curvature. In studying (c) three methods of 

 lubrication were adopted: (1) the flooded state, where the 

 slider stood in a pool of the fluid; (2) the primary film. When 

 a drop of lubricant with sensible vapor pressure is placed on a 

 clean plate, although the drop to all appearance remains where 

 placed without change, an invisible film nevertheless spreads so 

 as to cover the whole plate as is evidenced by the fall in friction ; 

 (3) lubrication by deposit from the saturated vapor alone. 



The results showed that the friction was independent of the 

 quantity of lubricant present provided there was enough to cover 

 the surfaces with the invisible primary film. Where the amount 

 was less than this critical value the fall of friction was propor- 

 tional to the concentration of the molecules in the gaseous phase, 

 indicating that each molecule exerts the same influence as every 

 other. The influence of chemical constitution (d) was found to 

 be unexpectedly simple. If /jl denote the coefficient of friction 

 and M the molecular weight, their relation is given by 



^— b—a M 



where a and b are parameters. The parameter a is independent 



