1895.] 



Investigation of the Laws of Attrition, 



25 



VI. " An Experimental Investigation of the Laws of Attrition." 

 By F. T. Trouton. D.Sc. Communicated by J. Joly, 

 F.R.S. Received July 5, 1895. 



The method of investigation employed in these experiments con- 

 sists essentially in rubbing two solid surfaces together under specified 

 conditions, and in finding the amount of material removed off the 

 surfaces in this way. The apparatus consisted in an arrangement by 

 means of which two parallel cylinders of the substances to be experi- 

 mented with could be rotated, while at the same time pressed together 

 with a known force. The amount removed was found by weighing 

 the cylinders before and after. 



The substances experimented with up to the present are all of a 

 non-metallic character. The results of the experiments may shortly 

 be summed up as follows : — 



1. The amount removed by attrition under otherwise similar 

 circumstances is proportional to the pressure. 



2. In each case there is a critical pressure below which two 

 surfaces when rubbed together tend to polish, and to gradually cease 

 losing material. 



3. The amount removed by attrition from a given substance when 

 rubbed by other kinds of substances harder than itself, depends (to 

 a first approximation) only on the properties of the substance itself, 

 and does not increase with the hardness of the other body. 



The first of these three permits of an absolute coefficient of 

 attrition, or shortly the attritivity, being defined as the amount 

 removed per unit area, during unit displacement, when two surfaces 

 of the same material undergo relative movement while pressed 

 together with unit pressure. 



The Aitritometer. 



The simplest form an apparatus for making experiments on 

 attrition could take would, apparently, be that of two plane surfaces, 

 which could be made to rub each other while pressed together, but 

 the difficulty of removing the attrited material makes some modifica- 

 tion necessary. The form of apparatus finally adopted consisted 

 essentially of two parallel cylinders, which could be rotated so as to 

 rub each other while pressed together by a known force. Oppor- 

 tunity is thus afforded during rotation of dusting off any of the 

 adhering material. This was effected by pads or wisps of cotton- 

 wool, held against the cylinders by means of small stiff brushes on 

 which the wool remains caught. Fig. 1 shows the apparatus 

 diagrammatically in plan. 



