Iodine Number. Genuine butter from 30·5 to 43·0 Oleomargarine „ 50·9 „ 54·9 Cocoa-nut oil 6·8 Lard 55·0 Mutton fat 57·3 Oleine 82·3 Olive oil 83·0 Pea-nut oil 96·0 Sweet-almond oil 102·0 Cotton-seed oil 108·0 Poppy oil 134·0 It has been proposed to differentiate between butter and oleomargarine by a determination of the proportion of glycerine contained. Liebschütz[36] employs the following process for this estimation: 10 grammes of the sample are saponified by heating with 20 grammes of barium hydroxide, until the water of crystallisation has been almost entirely expelled. Alcohol is then added with constant stirring; saponification quickly takes place, and is completed by evaporating the mass nearly to dryness. The glycerine is extracted with boiling water, the solution filtered, and the barium contained removed by means of sulphuric acid. The filtrate from the barium sulphate is then concentrated by evaporation, and the excess of sulphuric acid present neutralised by adding a little barium carbonate. The filtered liquid is now again evaporated to a small volume, and most of the salts present precipitated by addition of absolute alcohol. After filtration the alcoholic solution is evaporated over the water-bath, then dried at 100° until constant weight is obtained. It is finally ignited and the proportion of glycerine contained estimated by the loss in weight sustained. This process is certainly far from being exact, owing principally to the volatilisation of glycerine that occurs in the evaporation of its aqueous and even alcoholic solutions. The following results were obtained upon treating genuine butter and oleomargarine according to the above method:-- Per cent. Glycerine. Butter 3·75 Oleomargarine 7·00 Gelatine is said to have lately been used as an adulterant of butter, more especially of artificial butter. Its detection is a matter of some difficulty. The following method has been suggested. A considerable quantity of the suspected butter is boiled with water, the solution strained, a drop of acetic acid and a little potassium ferrocyanide added, and the liquid boiled until the precipitate formed becomes bluish in colour. The solution is then filtered hot and the filtrate examined for gelatine by adding tannic acid to, or conducting chlorine gas through it. A sample lately imported under the name of “butter preservative” was found by the author to consist of a dilute solution of phosphoric acid. The use of this agent does not, however, appear to be prevalent to any great extent.[37]