The fatty acids which separated in white curdy masses were thoroughly washed on a filter with cold water, about four litres, dried in vacuo over oil of vitriol, and weighed. The results of experiment show that butter fat yields the same proportion of insoluble fatty acids when saponified with or without the aid of heat.
3. Mr Gatehouse. Rapid Method of Detecting the Adulteration of Butter with other Fats. The following comparative method is based upon the insolubility of potassium stearate in alkaline solutions when the stearate has been produced at high temperatures:
Before applying the test it is essential to remove all curd, butter-milk, and salt, by washing with hot water or dissolving in ether. Twenty grains of the butter are placed in a large test-tube one third full with water boiled thoroughly and allowed to stand till the fat separates. The fat is either dissolved in ether, and after evaporation saponified, or the lower layer of the liquid is drawn off by a pipette as follows:—A thin glass tube is drawn out to
a fairly fine point and bent at the top to an obtuse angle. Whilst the butter is still liquid this nozzle is inserted into the bottom of the test-tube, placing the finger over the upper end to prevent any liquid from getting in till it reaches the bottom. When fairly cold the liquid may be withdrawn by a pipette attached to the tube. This process can be repeated till the washings are free from chlorides.
The saponification is effected by heating the purified butter with 1⁄3-1⁄2 of its own weight of pure solid potassium hydrate (purified by alcohol) to a temperature above 420° F.; applying the heat gently at first, and when the frothing ceases, heating it more strongly, till no further apparent action occurs. The ultimate temperature during saponification must be kept above 400° for some minutes, otherwise the sterate formed will be soluble instead of insoluble in the alkaline solution.
If the butter is pure, the colour of the residue will be at the utmost light yellow, but should the butter be adulterated to any extent, it may be almost black. Too much reliance must not, however, be placed on the colour.
After allowing the tube and its contents to cool, the mass is boiled with successive portions of distilled water till 6 oz. (or 200 c. c.) altogether have been used. If the butter is pure, a portion of this solution poured into a test-tube will present only a faint opalescence; if, on the other hand, the butter is impure, a decided opacity will be perceived, the degree depending upon the amount of adulteration.
The amount of adulteration in any sample is determined by first obtaining pure butter and adding to separate portions of it known per-centages of lard, &c. Each of these can be saponified as stated above; they are then corked up in tubes of equal diameter and labelled with the per-centage of lard they contain. On comparing them it will be seen that 2 per cent. of lard can be clearly indicated.
When a butter is analysed all that is wanted is to saponify, make up to the correct strength, and after cooling pour into a test-tube and compare with the specimen tubes.
4. Dr Redwood. The Determination of the Melting Points of Butter and other Fats. The apparatus in the form best suited for general use consists of a basin, two small beakers, and a thermometer. The author uses an enamelled iron basin about six inches in diameter, and three and a half inches deep. In this is placed a beaker four and a half inches deep and three inches in diameter, and within this beaker is placed another much smaller one, supported by its projecting rim on a disk of tinplate or copper, the outer edge of which rests on the mouth of the larger beaker. Some mercury is put in the smaller beaker to the depth of about an inch, and cold water into the larger beaker, so that its surface shall be half an inch or an inch higher than that of the mercury.