( 38) 



After the series of experiments with a charge of 8 kgr. block I 

 presented a running surface scarred by irregular grooves and scratches. 

 On block II the rectangular crystals stood out in i\ relief, similar 

 to that, produced by etching with hydrochloric acid. They were 

 smooth and bright, the interstices deadened by small scars or dimples. 

 On block III the particulars shown by I and II were found 

 combined. 



An unexpected result was obtained by examining the metallic 

 sediment from the oil that had been used as lubricant. Mixed with 

 fine dust (essentially tin) were found: in sediment from block I 

 shavings, threads and angular fragments; in sediment from block II 

 spherical and egglike bodies (0.08—0.1 mm.), looking like small 

 drops of mercury; in sediment from block III spheroids and angular 

 fragments. A few of the spheroids from block II were subjected to 

 microchemical tests and found to consist of tin with a considerable 

 admixture of antimony. 



These observations suffice to explain the slow increase of tempe- 

 rature in block II: the oil has been more evenly spread, owing to 

 the peculiar relief, developed on the running-surface of this block, 

 and at the same time a ball cushion has been formed, whereby 

 rolling has been brought in the place of sliding friction. Spheroids, 

 similar to those of block II were formed in experiments with mod(d 

 bearings of magnolia metal (77.8 «/p Pb, 16.3% Sb, 5.9 o/^ Sn) and 

 of aluminium brass, but not with bearings of common brass and of 

 grey cast iron. In this way I have been able to trace their origin 

 to cubical or polyhedric crystals, scattered in a softer metal and 

 accompanied by smaller crystals of a hard and brittle alloy. In 

 Babbits metal fragments of the brittle rods of bronze act as a 

 grinding powder, undermining and rounding the rectangular crystals 

 of the compound Sb Suj, in the same way, as pebbles are formed 

 in the bed of a river. The tin comes in as a soft cement, possibly 

 its powder has also a favourable influence, augmenting the viscosity 

 of the lubricant. Metal of coarse structure (cast in overheated moulds) 

 is not evenly eroded; the majority of the rectangular crystals, w^eakened 

 by cracks, are scarred and crushed, instead of being rounded and 

 loosened. 



Further reasoning would be misplaced, as it may be expected, 

 that continued experiments and observations in the directions, pointed 

 out above, will speedily throw more light on the subject. 



