It was thus found that 100 grammes of the oil require 0.34 gramme of caustic potash to neutralize the free acid. Mr. W. H. Deering (_Journ. Soc. of Chem. Industry_, Nov., 1884) states that in seven samples of olive oil examined by him, the minimum number for acidity was 0.86 per cent., and the maximum 1.64 per cent., the mean being 1.28 per cent. Tea oil compares favorably with olive oil, therefore, in respect of acidity, a quality of which note has to be taken when considering the employment of oil as a lubricating agent. (4.) _Saponification of the Oil._--Considerable light is thrown on the composition of a fixed oil by ascertaining how much alkali is required to saponify it. In order to estimate this, a known excess of alcoholic solution of potash is added to a weighed quantity of the oil, contained in a stout, well-closed bottle (an India-rubber stopper is the most convenient), which is then heated in a water oven until the liquid is clear, no oil bubbles being visible. Phenol-phthalein solution being added, the excess of potash is estimated by carefully titrating with standard hydrochloric acid solution. It was thus found that 1,000 grammes of oil would require 195.5 grammes of caustic potash to convert it entirely into potash soap. Koettstorfer, to whom this method of analysis is due, gives 191.8, and Messrs. F. W. and A. F. Stoddart the numbers 191 to 196, as the amounts of caustic potash required by 1,000 parts of olive oil. The numbers given by niger seed, cotton seed, and linseed oils are very similar to these. These oils differ from olive and tea oil, however, in having a higher specific gravity, and in the property they possess of drying to a greater or less extent on exposure to air. (5.) _The Fatty Acids Produced._--A solution of the potash soap was treated with excess of hydrochloric acid, and after being well washed with hot water, the cake of fatty acids was dried thoroughly and weighed. These, insoluble in water, amounted to 93.94 per cent, of the fat taken. The proportion dissolved in the water used for washing was estimated by titration with alkali; the quantity of KOH required was insignificant, equaling 0.71 per cent, of the fat originally used. This portion was not further examined. The insoluble fatty acids amounted, as last stated, to 93.94 per cent. Pure olein, supposing none of the liberated acid to be dissolved in water, would yield 95.7 per cent. of fatty acid.