IN view of the indeterminate chemical nature of "gum" in gasoline, the most that may be expected from any type of estimation of present gum content is that results of tests on the same sample shall be repeatable within reasonable limits and that the result obtained on a known blend of fuels shall be the proportional arithmetic mean of the gum contents of the constituents. With regard to ordinary practice, however, a suitable method of test must satisfy. quite a number of requirements, the most important of which are (a) That the test should necessitate only a simple type of apparatus, easily cleaned and assembled, and cheap-at least as regards replacements (b) That the test should be relatively easy to carry. out and not require a high degree of manipulative skill; (c) That it should be possible to make a number of tests simultaneously, the final results being available well within the normal shift of eight hours, and (d) That the method should be suitable for the.. evaluation of the results of potential gum tests. It was with these considerations in mind that the Sub-Committee 1 appointed to. deal with the estimation of gum in, motor fuels containing cracked spirit, commenced its work. Various methods were available for consideration; for example, the flash evaporation method of Thole and Norris,2 the high temperature method B 3 suggested by the A.S.T.M., the steam oven method 4 and the air-jet steam-bath method.5 Of these, the flash evaporation method was considered to be the one which most nearly approximated to theconditions of evaporation in the induction manifold of a petrol motor. However, the somewhat complicated apparatus required, together with the necessity for a high degree of manipulative skill and for continuous attention, caused its rejection. The high temperature method of the A.S.T.M. was rejected for similar reasons, and the steam oven test, although somewhat simpler, did not seem to lend itself to easy standardization. It was thus generally indicated that some simple type of glass dish test was desirable, provided that consistent results could be obtained by different operators working in separate laboratories. Accordingly, in order to assess the glass dish methods in current use in the various laboratories, samples of an unstable cracked gasoline were circulated to the members of the Committee, to be tested by the method used by each individual, the following being a summary of the results obtained Volume Evaporated.

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