The foregoing method can be applied quantitatively by determining the strength of the alcohol which will keep in equilibrium a drop of the fat under examination. Since the difference between 59·2 and 53·7 is 5·5, the difference between the strength of the alcohol used and 53·7, divided by 5·5 (or multiplied by 0·18), will give the proportion of oleomargarine present. For example, if the globule is held in equilibrium at 15° in 57 per cent. alcohol, the sample contains about 60 per cent. of oleomargarine, for (57 - 53·7) × 0·18 = 3·3 × 0·18 = 0·594 or, say, 6/10. The melting-point of butter is below that of most of its fatty adulterants; as previously stated, it varies from 28° to 37°. The determination is made either in the ordinary manner by means of a fine tube, or a little of the chilled sample is attached to a looped platinum wire, placed near the thermometer-bulb, in water which is gradually heated until fusion takes place. Blyth gives the following table of the melting-points of various fats:-- ° Butterine 31·3 Cocoa butter 34·9 Butter (average) 35·8 Beef dripping 43·8 Veal dripping 47·7 Mixed 42·6 Lard, from 42 to 45 Ox fat, from about 48 „ 53 Mutton fat, from about 50 „ 51 Tallow 53·3 Numerous qualitative tests have been proposed by various authorities for the detection of foreign fats in butter, of which the following are perhaps sometimes of use. It should be added that the value of these tests, when applied to mixtures, is limited and very uncertain. 1. A little of the sample is heated in a test-tube: pure butter froths and acquires a brownish colour; with foreign fats there is but little foaming, and, although the caseine present darkens, the liquid itself remains comparatively clear. 2. If a sample containing oleomargarine is melted and the oil burned in an ordinary lamp-wick, a decided odour of burning tallow will be produced upon extinguishing the flame. Specimens of real butter, however, have been found to also emit a tallow-like odour. 3. The melted sample is filtered and treated with boiling ether; pure butter fat dissolves much more readily than do lard and tallow. Upon adding methylic alcohol to the solution the latter fats are precipitated, whereas pure butter will remain in solution. 4. If the filtered fat is distilled with a mixture of alcohol and sulphuric acid, the distillate will possess the odour of butyric ether _in a very marked degree_, in case it consists of butter.[27] 5. The strained fat is treated with a solution of carbolic acid (1 part acid and 10 parts water): genuine butter dissolves to a clear solution; beef, mutton, and swine fat form two layers, the upper one becoming turbid upon cooling.