A. ORDINARY EXAMINATION OF FATS. (1) Estimation of Moisture in Fats.-25 grm. of the fat are weighed into a carefully tared porcelain dish, which is then placed over a low gas-flame, and stirred with a thermometer, taking care that the temperature is maintained above 100° (212° F.), but not exceeding 110° (230° F.). This is continued until no more bubbles of vapour escape, indicating that all the moisture has been expelled ; the whole is then allowed to cool. When cold, the ther mometer is carefully drawn out, and any fat remaining attached to it is scraped off and returned. If, however, an instrument with a long narrow bulb be used, and it be carefully loosened by gently turning it round, usually no fat will adhere on withdrawing it. The dish plus the fat is then weighed, and the tare being deducted, the remainder is the dry fat in the 25 grm. taken, which, multiplied by 4, gives percentage of pure fat, and the difference between that and 100 represents the percentage of moisture.
(2) and (3) Estimation of Organic and Mineral matters present as Impurities in Fats.—This applies to the estimation of curd and salt in butter, and of fibrous and mineral impurities in oils and fats, and is thus conducted. The contents of the dish already used for moisture are melted, and the melted fat is poured off as far as possible without disturbing the sediment. Some petroleum-spirit, rectified at a temperature not exceeding 87° (188° F.), is poured into the dish, and the whole is well stirred, and transferred to a previously weighed filter. By means of successive portions of petroleum, the whole of the contents of the dish are washed on to the filter, and all traces of fat are completely washed away from the other matters, which remain on the paper. The filter is then dried at 100° (212° F.), weighed, and the tare having been deducted, the remainder is organic matter plus mineral matter (or, in a butter, curd plus salt).
The filter and contents are then transferred to a previously weighed platinum crucible, and heated for some time to dull redness, till the ash becomes greyish-white. The crucible and ash are weighed, and the weight of the former being deducted, the difference is mineral matter (or, in a butter, salt). The mineral matter thus found is deducted from the former result, and the difference is the organic matter, and each multiplied by 4 gives the 'respective percentages.
(4) Estimation of the total Fatty Acids in any ordinary Fat or Fixed Oil not containing Glycerides of Soluble process, which is also applicable to the estimation of the total insoluble acids in a fat containing glycerides of soluble acids, divides itself into two beads, as follows :— (a) Preparation of the sample.—If the sample be a perfectly clear and dry oil, it is at once ready for use ; but if it be at all turbid, or if a solid fat, a portion must be placed in a tube, and kept in the water-oven below 100° (212° F.), until any moisture and heavy suspended impurities have settled to the bottom. A well-dried filter-paper is then placed in a funnel over a dry beaker, also in the water-oven, and the nearly clear upper portion of the melted fat is filtered, until a sufficient quantity is thus obtained fit for analysis.
(8) Process of analysis.—A perfectly clean and dry 5-oz. flask is accurately tared on the balance, and 5 grm. of the melted fat are carefully weighed into it. (It is not important exactly to a frac tion, but as nearly 5 grm. as possible should be taken, and, in any case, the weight must be noted with
great care.) To this, are then added about 30 c.c. of methylated spirit 60 o.p., and a fragment of caustic potash weighing about 2 grm., and the flask is then placed in a basin of boiling water, until the whole of both fat and potash have dissolved, and the addition of a little water produces no permanent turbidity, which will be attained within 10 minutes, as a rule. The contents of the flask are then poured into a basin, and the flask is washed out with repeated quantities of boiling dis tilled water, until the contents of the basin measure about 250 c.c., and no trace of soap remains in the flask. The basin is then placed over a low gas-flame, and evaporated till it ceases to give off spirituous vapours, a little boiling distilled water being added, if necessary, to prevent too great a loss by evaporation. The contents of the basin are then transferred to a 600-c.c. flask (1 pint size) the basin is washed with boiling water, and the washings are added to the flask. A slight of hydrochloric acid is then added, the whole is boiled, and shaken with a circular motion until a perfectly clear layer of fatty acids separates on the surface, and is set to cool. If the acids solidify on cooling to a good solid cake, well and good; but if not, a carefully weighed quantity of pure white wax must be added, and melted with the layer of fatty acids, so that, on cooling, they solidify firmly. This is always necessary in the ease of oils, but not usually with solid fate. The month of the flask is then covered with a piece of ordinary cambric, held in situ by an indiaruhber ring under the lip, so as to form a filter, and, the cake having been detached from the flask by a gentle motion, the watery liquid is poured off. Some boiling distilled water (about 200 c.c.) is then poured into the flask, and the whole is again boiled, well shaken, and cooled. The liquid below the cake is passed through the cambric as before, and this washing is repeated until the fluid collecting below the cake ceases to give a cloud with argentic nitrate. Care having been taken that, st the last pouring off, the cake has not been at all broken, the flask is inverted, and left to drain for the night with the cambric still attached. In the morning, the flask is placed in the water-oven till the cake has thoroughly melted, the cambric is removed, and the fat is then carefully poured into a dry and accurately tared platinum capsule, dried in the water-oven at 100° (212° F.), and weighed. The cambric is put into the flask, and the fat still adhering to both is washed out with small successive quantities of petroleum-spirit into a previously weighed small beaker. The petroleum is then evaporated off on the water-bath, the residual fat is weighed, and its weight is added to that of the main quantity already weighed in the capsule. The united weight then represents the total fatty acids in the quantity of fat taken, and is calculated to percentage by multiplying by 100, and dividing by the weight taken for analysis. It sometimes happens that an obstinate little globule of water forms below the melted acids in the weighing-capsule, and refuses to dry up ; but this is easily removed by adding a little absolute alcohol, and again drying in the water-oven. The alcohol thus used carries off with it in volatilizing the little trace of moisture remaining.