132 THE ANALY8T. ON DR. KOETTSTORFER’S METHOD FOB THE EXAMINATION OF BUTTER FOR FOREIGN FATS. BY G. W. WIGCNER, F.C.S. SINCE the publication of this process in the ANALYST laat month, I have carefully tested it on various samples of genuine butter and of adulterated butters, and other fats, such as dripping or lard, and find it not only a quick and liondy process, but a reliable one. The point of neutrality is very sliarply indicated by the phenol-yktalein, and byTHE ANALYST.133 working on moderate quantities, say 50 grains, or thereabouts, of tlie filtered fat it is possible to obtain a mnch greater relative degree of accizracy than by the determination of the fatty acids. I fiiid it advisable, after saponification, to dissolve the soap in hot water and titrate mliile still hot ; by this meaiis the precipitation of the fatty acids during the process of thation is prevented, and the finish of the neutralization seen more distinctly.I find that my samples of butter require a slightly larger percentage of potash to saturate them tliaii the samples iiivestigated by the author of the process, but the difference is small, and there is about 3.0 pcr cent. difierence between the potash required by any fat I have yet tested, and that required by a genuine sample of butter.