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Microscopic examination (X 320) at room temperature of the "filtrates through cotton at 65°to 75°C." from numerous used crankcase oils, taken at random, showed no dark particles in most of them; a small percentage showed a few isolated particles estimated to be not more than 2 per cent of the amount visible in the samples before the filtration. The absence of the dark particles proves that the oils while filtering at the elevated temperature did not dissolve sludge which they could not retain in solution at room temperature. Since crankcase oils in use are commonly at these and even higher temperatures and hence have the opportunity to act on the sludge, the additional warm period during filtration should not materially influence the solution of the sludge in the oil.Attempts at determining undissolved sludge by filtering the undiluted sample through a weighed filter, followed by wash-ing the residue on the filter with a suitable solvent, failed completely. The fine sludge of the sample soon came through the filter or clogged it completely. Literature Cited(1) Am. Soc. Testing Materials, "Standards on Petroleum Products and Lubricants," D95-30, 1936.

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