A vast amount of research work and experimentation has been done on the problem of fat spoilage, the reactions involved, and the various tests bearing on rancidity.It is impossible, in a paper of this kind, to give a comprehensive bibliography or to mention more than a small portion of the work done. However, some of the more pertinent references are given.In recent articles, Vibrans 2~ and Wheeler 22, list a large number of references and discuss the work of various investigators briefly.The work covered by this paper grew out of a demand for a quick method for comparing the stability or keeping qualities of lard samples. At present several methods for determining the stability of fats are in use in the baking and packing industries, all of which are open to one or more objections.The methods in common use are:1. Incubation Tests--such as Schaal's and similar tests :In these tests the fats are exposed to the air in a heated incubator and examined organoleptically at regular intervals until they become rancid. Such tests are objectionable because of the time involved, and because the results are dependent entirely on personal judgment. Oxygen Absorption Tests 1 to 12 lnolu~ivo:In these tests either the amount of time required by the fat to absorb a certain amount of oxygen, or the amount of oxygen absorbed in a fixed time is taken as indicative of the keeping qualities of a fat. These methods require complicated and expensive apparatus and produce results which are influenced by changes in absorption rate due to changing pressure and the presence of volatile oxidation products.3. Color Reaction Tests--such as the Kreis ~, modifications of it 14-~5 and the Schiff tests 16-17.These are tests which produce a color reaction in the presence of the aldehyde products of fat decomposition and have been shown to give no indication of the keeping qualities of a fresh fat. Tests

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