170 THE ANALYST. DETERMINATION OF FREE ACID IN OILS. BY 1;. ARCHBUTT, F.C.S. IN the ANALYST for September, 1883, and again in the number for June, 1884, there appeared papers translated from foreign journals, descriptive of certain methods for estimating Free Fatty Acid in Oils. As neither of the methods is so simple or satisfactory as it might be, a description of the process which I have constantly used for Borne years past may be of service to some readers of this journal. I use two tall, narrow-mouthed, colourless glass bottles, of about 400 C.C. capacity. One bottle is divided, by file marks on the side, into four parts of about 100 C.C. capacity each. An ordinary normal soda solution (40 grammes NaHO per litre) is used for the ti tration. The divided bottle is filled with re-distilled methylated spirit, a few drops of phenol- phthalein solution added, and normal soda run in, drop by drop, until the liquid is coloured a faint pink.This quantity of neutralised alcohol serves for four titrations. The other bottle is counterpoised on a large balance, and 50 gi*ammes of theoil are weighed into it. 100 C.C. of the neutral spirit is added, and a few drops more phenol* phthalein, and then normal soda is run in until the mixture, after being violently shaken, is permanently coloured just pink. One drop of soda, ( z . 0 3 per cent. of oleic acid) in excess, mill produce this result. The number of c.c.’s employed X-562 gives the percentage of free fatty acid, stated as oleic acid. The determination can thus be accurately made in a few minutes, with very little trouble.The bottle containing the oil and alcohol, when emptied and allowed to drain for a few seconds, is ready for the next sample. In the case of palmoil (which is often coloured red), and other solid fats, the process requires to be slightly modified. If the sample be very red, it will not b? possible to work on a much larger quantity than five grammes, and as a rule it will be found most convenient to take from 5 to 10 grammes of any solid fat. The result will not be quite so accurate as by using a larger quantity, but it mill be aufficiently so for most purposes. My plan is to melt some of the €at in a beaker, and weigh 10 grammes into a short wide-neoked flask, of about 150 C.C. capacity. 20 C.C. of neutralised spirit are added, and some phenol-phthalein, and then normal soda, as before, until the pink colour is permanent after vigorous shaking.During the titration, the fat is kept in a melted condition by warming the mixture occasionally. Even when palm oil is very red, withTHE ANALYST. 171 a, little care it is quite easy to detect the change. I have proved by experiment upon neutral palm oil that no saponification of the fat takes place. The number of c.c.’s of soda required x *255 gives the corresponding weight of free palmitic acid in the quan- tity of oil taken. Some oils are liable to contain a small quantity of Free Hifieral Acid which has not been washed out after refining. It is obvious that the process described above makes no distinction between mineral and fatty acid, but simply estimates the total acidity. Free mineral acid may, however, be readily detected and estimated by shaking the oil with water and methyl orange, instead of spirit and phenol-phthalein, the former indicator being unaffected by fatty acids. In this case it is better to separate the oil from the vater before titrating. In the caae of dark coloured mineral oils this precaution is essential. I The following factors will be useful :- 1 0.0. of Normal Alkali is equivalent to -281 gramme Oleic Acid. [ -265 ,, Palmitic Acid. * ‘283 ,, Stearic Acid. *O = 16*9G