The preceding process is also imperfect in not effecting the detection of cocoa-nut oil, which affords only about 86 per cent. of insoluble fatty acids, and although the presence of any considerable proportion of this oil in butter would probably be indicated by the decreased melting point of the admixture, an estimation of the soluble fatty acids is by far the most reliable means for its detection. For this determination Reichert’s method[32] is eminently adapted. In this process advantage is taken of the facts that the amount of soluble acids in a mixture of fat bears a direct relation to the proportion of genuine butter present, and that, if the aqueous solution of a saponified fat is decomposed by an acid and heated to boiling, the greater portion of the soluble acids escape with the watery vapours and can be collected and determined in the distillate. The details of this method are essentially as follows:—2½ grammes of the filtered sample are introduced into an Erlenmayer flask together with 1 gramme of potassium hydroxide and 20 c.c. of dilute (80 per cent.) alcohol, and the mixture is heated over the water-bath until complete saponification is effected, and the alcohol entirely removed. The soap thus formed is dissolved in 50 c.c. of water, and decomposed by adding 20 c.c. of dilute sulphuric acid (1:10). The flask is next connected with a Liebig’s condenser and the contents carefully distilled until 50 c.c. have passed over. The distillate is now freed from any insoluble acids possibly present by filtration; it is then titrated with decinormal soda solution, a few drops of litmus solution being employed as an indicator. As the result of numerous tests, it has been found that genuine butter, when examined by the above method, requires from 13 to 15 c.c. of the decinormal solution. The following are the number of c.c. required by various other fats:—
| Lard | 0·2 |
| Rape oil | 0·25 |
| Kidney fat | 0·25 |
| Olive oil | 0·3 |
| Sesamé oil | 0·35 |
| Oleomargarine | 0·7 to 1·3 |
| Cocoa-nut oil | 3·70 |
Dr. Elwyn Waller[33] modifies the foregoing method of procedure by adding 50 c.c. of water to the contents of the flask remaining after the first distillation, and again distilling off 50 c.c., the process being repeated until the final distillate neutralises only 0·1 c.c. of the decinormal alkali. With butter fat, it was found that the first distillate contained about 79 per cent. of the total volatile acids present. By means of this modification, a distinction between the rate of distillation of the volatile fatty acids of different fats is possible. The non-volatile acids left in the flask are washed several times with water, in order to remove the glycerine and potassium sulphate present, and are then dried and weighed.
For estimating the percentage of pure butter fat in a sample of mixed fat, Reichert employed the formula: B = 7·3 (m - 0·3), in which m is the number of c.c. of soda solution used in the titration.
Baron Hübl[34] has recently suggested a method for butter testing, which is founded upon the fact that the three series of fats (acetic, acrylic, and tetrolic), unite in different proportions with the halogens (iodine, bromine, and chlorine), to form addition products. Iodine has been found especially well adapted to the examination of fats. The standard solution employed is prepared by dissolving 25 grammes of iodine in 500 c.c. of 95 per cent. alcohol, and adding to the solution a solution of 30 grammes of mercuric chloride in 500 c.c. of alcohol. The reagent is then standardised by means of a solution of 24 grammes of sodium hyposulphite in 1 litre of water. The test is applied as follows:—1 gramme of the sample under examination is introduced into a flask and dissolved in 10 c.c. of pure chloroform. The iodine reagent is then gradually added from a burette, the mixture being well shaken, until the coloration produced indicates that an excess is present, even after standing for about two hours; 15 c.c. of a 10 per cent. potassium iodide solution and 150 c.c. of water are then added and the excess of iodine present determined by means of the sodium hyposulphite solution, and deducted from the total quantity used. The amount of iodine (in grammes) absorbed is calculated to 100 grammes of the fat; this is termed the iodine number. The examination of numerous samples of genuine butter and oleomargarine, and other fats, made at the laboratory of the New York State Dairy Commissioner, furnished the following results:[35]—
| 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.