(3) Chemical analysis for the amounts of soluble and insoluble acids.—For this purpose, the following reagents are necessary:— a. Semi-normal volumetric sulphuric acid, containing 49 grm. per litre. This is made by weighing out 50.6199 grm. pure oil of vitriol, sp. gr. 1.843, and diluting with distilled water to 1 litre. Each c.c. of this acid will represent 0.088 grim of soluble hutter-acids, calculated as butyric acid, or 0.09 of soluble butter-acids on the basis that they are 90 per cent. butyric and the rest chiefly caproic.
b. Volumetric normal solution of sodium hydrate, containing 40 grm. real NaHO per litre, and made by dissolving say 45 grm. of ordinary caustic soda in a litre of distilled water, then filling a burette with this solution, and running it into 100 c.c. of the volumetric sulphuric acid placed in a beaker, to which a few drops of alcoholic solution of phenol-phthallein have been added, until it produces a pink colonr. The number of c.c. of the soda solution used having been noted, ten times that quantity is placed in a test mixer, and made up to 1 litre with distilled water. Each c.c. of this alkali will now represent 1 c.c. of the acid.
c. Volumetric normal solution of potassium hydrate in methylated spirit, made by dissolving 60 grm. of ordinary caustio potash in 1 litre of methylated spirit, checked, and made up with spirit, exactly as directed for the sodium hydrate solution. It is to be preserved in a well-stoppered bottle, and always checked again before use.
d. An ordinary solution of barium chloride.
The process is performed as follows :-5 grin. of melted and purified butter-fat (as directed under "total fatty acids ") are weighed into a 5-oz. flask, 50 c.c. of the alcoholic potash (c.) are carefully added from a burette, and the whole is boiled on a water-bath for about 15 minutes, or until the addition of a little water produces no turbidity. This solution is washed into a long, narrow, graduated measure with successive quantities of distilled water, till the whole measures 300 c.c., and it is than divided into two parts of 150 c.c. each. In part A, the insoluble acids are estimated ; in part B, the soluble.
Part A is treated with solution of barium chloride, until no more precipitate forms ; the precipi tate is collected on a filter, and well washed with warm water. It is then transferred to a " Muter's oleine tube" (see Fig. 1045) having a wide mouth, by washing it in with distilled water, and allowed to settle. As much as possible of the water is drawn off by inclining the tube forward and running off the clear water at the stopcock ; 20 c.c. of diluted hydrochloric acid (1 acid to 2 water) are added,
together with 100 c.c. of pure ether ; the stopper is introduced, the tube is well shaken, and then allowed to settle till the ethereous solution separates. The amount of the ethereous solution is noted, and a definite quantity (say one-half) is drawn off into a tared platinum capsule ; the ether having been evaporated off, the residual acids are weighed, all as already directed for the estimation of oleic acid in non-drying oils. The weight, first doubled (if half the ethereous liquid has been used), and then multiplied by 40, gives the percentage of the insoluble acids in the butter-fat. The amount of adulteration is best calculated on this result by the following formula, in which, P is the weight per cent. of insoluble acids found, and x the percentage of adulteration.
(P — 88) x 100 7.5 Looking, however, to the fact that the insoluble acids in butter increase by age and rancidity, no article should be positively condemned which shows less than 90 per cent. of insoluble fatty acids. Once tho adulteration is thus rendered certain, its percentage should be calculated, as above, on the ordinary standard of good butter.
If preferred, the insoluble acids in butter may be estimated by the process already detailed for total fatty acids in ordinary oils and fats, in section (4).
Part B is diluted with another 100 c.c. of water, placed in a flask, brought under a burette containing the volumetric sulphuric acid (a), and 50 c.c. are run in. The flask is then attached to an upright condenser, boiled until the insoluble acids separate in a clear oily layer, and then allowed to cool. The cake is detached, and the fluid is run off through a filter, made as directed in section (4), by fixing a piece of cambric over the mouth of the flask. Another 100 c.c. of boiling water is then added to the cake, and the whole is again boiled under the upright condenser ; when cooled, the liquid is passed through the same filter. This operation is repeated, and the united filtrates are brought under a burette containing the volumetric sodium hydrate (b), and, a few drops of alcoholic solution of phenol-phtballein having been added, the solution is run in. When a pink colour has been produced, the number of c.c. used is noted, and this number, multiplied firstly by 0.09 and secondly by 40, gives the percentage of soluble fatty acids in the butter-fat.