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The same process is applicable to the insoluble fatty acids, a weighed quantity from 0-2 to 0-4 of the fatty acids being dissolved in chloroform and treated as above. The following are a few iodine values for various fats and oils:

Linseed Oil,

Castor Oil,

Iodine number.

Olive Oil,

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158'0

84.4

82.8

59.0

55.3

51.5

40.0

34.0

31.0

31.0

8.9

4.2

In fats, like butter-fat, in which it is believed there are no other unsaturated acids than oleic, olein and the oleic acid can be in this way estimated.

The theoretical amount of iodine absorbed by oleic acid is 90-07 per cent., and the theoretical iodine value for olein is 86.20. Hence, if the iodine value of a fat equals 1, the percentage of olein will be found from the following formula

100 × 1

Olein = 86.2

Or, simpler still, the iodine value multiplied by the factor 1·1601 gives the olein. Similarly the amount of oleic acid in the fatty acids is found by multiplying the iodine value found by the factor 1.1102.

Hehner has proposed to treat fats with bromine, and weigh the product. 1 to 3 grms. of the fat are introduced into a widemouthed flask, and dissolved in a few cubic centimetres of chloroform; then pure bromine is added drop by drop until in excess. The flask is then heated in the water bath, and the bromine driven off by adding from time to time a little chloroform. Finally the brominised fat is dried at 125°, and weighed. To compare the results with those obtained with iodine, the gain in weight is multiplied by that is, 1587; the results

fairly agree.

127

80

The Cryoscopic Method of examining Butter-Fat.-Raoult's method of determining molecular weights is applicable to butter-fat, and may be used as a means of distinguishing it from margarine. F. Garelli and L. Carcano, using benzene as a solvent, and considering the constant for benzene to be 53 (it is usually taken as 49), found that pure butter had a moleAnalyst, xx., p. 50.

#

cular weight of from 696 to 716, while margarines ranged from 780 to 883.*

A'

The apparatus required is (1.) a Beckman's thermometer, D (fig. 39); this thermometer has a mercury reservoir at the top, e, so that variable amounts of mercury may be introduced into the lower bulb; it has a range of only 5 or 6 degrees divided into tenths; (2.) a tube with a side limb, A A'; and (3.) a wide test-tube into which the first one fits, so as to (as it were) jacket it with air. The whole is supported in a wide beaker, in which the freezing mixture is placed, and suitable stirrers, C and r, provided. The first thing is to ascertain the freezing point of a known weight of the solvent. The tube with side limb is weighed on the balance, and then about 20 grms. of the solvent are introduced, and the tube with its contents again weighed; the weight subtracted from the tare gives the amount of liquid. Some ice and salt and water are placed in the beaker, and the whole apparatus arranged as in the diagram. The mercury of the thermometer gradually falls, and as it falls both stirrers must be worked; on approaching the freezing point the thermometer becomes for a moment stationary, then suddenly rises, and then becomes stationary to again fall; when it last becomes stationary is considered the freezing point of the liquid; the tube is taken out, the liquid allowed to melt, and the operation repeated once or twice, the mean of the determinations being taken. Next from 5 to 8 grm. of the butter, or other fat, is dissolved in the same liquid, and the operation again repeated; this time there will be a difference of one or more tenths of a degree in the freezing point; it will be lower than when operating on the pure substance; this lowering is the molecular depression. The molecular weight is calculated by means of a constant, which, for the chief solvents, has already been ascertained. The two solvents applicable for butter are benzene, for which the constant is usually taken as 49, and paraxylene,† which may be taken as *Analyst, March, 1894.

Fig. 39. Cryoscopic apparatus.

+ Paterno and Montemartini, Gazetta Chimica Italiana, xxiv., ii., p. 197.

43. Of the two solvents, paraxylene is much to be preferred, for it has the low freezing point of about 16° and the high boiling point of 136°; hence, although expensive, it is readily recovered with but little loss.

The author has made several determinations of the cryoscopic value of butter-fat; but with paraxylene has obtained much lower values than Garelli and Carano. He is inclined to put the average molecular weight of butter-fat at about 580.

An actual example of a cryoscopic determination with paraxylene will illustrate the above remarks:

Weight of paraxylene taken,

:

Weight of butter-fat dissolved in the above,
Depression of freezing point,

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If M equals the molecular weight, C the constant, G the per cent. of substance dissolved, and t the depression, then the molecular weight, M, is found from the equation

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In the above example, replacing the letters by the experimental values

*

5.528 × 43
41

= 579.8

Summary. In any case in which the adulterant is moderate in quantity, up to 15 per cent. for example, the analyst will have to exert all his skill, and analyse the butter-fat very thoroughly— and the methods of taking the melting-point, the amount of potash used up by a gramme of the fat, the specific gravity, the refraction angle, the soluble and insoluble acids, the Reichert distillation process, the iodine absorption may all have to be used, for small percentages of mixtures can only be detected by carefully considering a number of indications. Single tests may be used for sorting butters, but are not to be relied upon. It is fairly easy to make mixtures of certain fats which will yield the proper quantity of insoluble acid, and which would pass the iodine test, the specific gravity, and the Koettstorfer tests, but not at all easy to make a mixture which will pass also the Reichert.

LEGAL CASE.

Somerset House standard for water in butter.

At the Bath Police Court (January, 1879), a dairyman had been summoned for selling butter, the proximate analysis of which showed a considerable addition of water. An appeal to Somerset House elicited the following certificate:-"We hereby certify that we have analysed the butter, and declare the results of our analysis to be as follows:

*The false butters used to be for the most part either all margarine or heavy percentages of margarine, but now there are many mixtures in commerce containing only small proportions of margarine.

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"The results of our analyses of numerous samples of ordinary commercial butters obtained from different parts of the country, including the south of England, show that the proportion of water present is very variable, and that it occasionally amounts to as much as 19 per cent."

Water in Irish butter.

A number of prosecutions for water in Irish butter were heard at the Manchester Police Court in 1894, before the Stipendiary, Francis John Headlam, Esq., the cases occupying seven days. Most of the leading analysts gave evidence. The cases were decided variously, according to the circumstances of a warranty or otherwise. In two cases in which there was a discrepancy in the analysis by two different analysts, the magistrate stated that he would have convicted on 21 per cent. of water; the amounts of water on which the prosecutions were based varied from 21 to 26 per cent. The Corporation of Manchester published the shorthand notes of the proceedings.

BIBLIOGRAPHY.

ANGELL, G., and HEHNER, 0.-"Butter: its Analysis and Detection." 1st ed., Lond., 1874; 2nd ed., 1878.

BENEDIKT, R.-Chemical Analysis of Oils, Fats, and Waxes. Translated and enlarged by J. Lewkowitsch, F.I.C. Lond., 1895.

BESAIRA.-Sui metodi a distinguere il burro artificiale dal burro naturale. Lodi, 1888.

BLYTH, A. WYNTER.-Easy and Rapid Method of Manipulating the Fatty
Acids. Analyst, ii., 1878.

On the Figures or Patterns which Liquid Fats assume under certain
Conditions. Analyst, 1880.

BLYTH, A. WYNTER, and ROBERTSON.-The Electrolysis of Butter-Fat.
Journ. Chem. Soc., 1889 (Proc.), 5.

BOCKAIRY, LADAN. "Beurre" in Girard and Dupré's "Analyse des matières alimentaires." Paris, 1894.

CROOK, W. G.-A New Method of distinguishing Butter from some other Fats. Analyst, 1879.

Dietzel, u. M. G. Kriesner.-Zeitschrift f. an. Chem., 1879.

DUPRÉ, A.-The Composition and Analysis of Butter-Fat. Analyst, 1, 87,

114.

Foods and Food Adulterants.

Bull, No. 13, 1887.

U.S. Department of Agriculture.

FABER, H.-On Water in Danish Butter. London, 1895.

Fox, W., and J. A. WANKLYN.-Butter Analysis. Analyst, 1883, 73.
HAGER, H.-Pharm. Central. Halle, xviii., 413.

JEAN.-Chimie analytique des matières grasses. Paris, 1892.

JONES, E. W. T.-Butter-Fat: its Analysis and Composition. Analyst, ii., 1878, 19, 87; Influence from the Decomposition of Butters through Age on the Specific Gravity of the Fat, &c. Analyst, 1879. KOETTSTORFER, J.-Neue Methode zur Untersuchung der Butterfett auf fremde Fette. Zeitschrift f. anal. Chem., 1879, 199, 431. Analyst, 1879, p. 106.

KRETSCHMAR, M.-Deut. Chem. Ges. Ber., x., 2091-2095.

MEDICUS, L., u. S. SCHERER.-Zeitschrift f. anal. Chem., 1880, 159.
MILNE, J. M.-Notes on the Analysis of Butter. Analyst, 1879, 40.

MUTER, J.-Butter Analysis. Analyst, 1877, p. 7.
PERKINS, F. P.-Analyst, 1879, 142.

REDWOOD.-On the Determination of the Melting-points of Butter and other Fats. Analyst, 1, 1877.

REICHERT, E.-Butter-Prüfung nach Hehner's Princip. Zeitschrift f. an. Chem., 18, 64.

REINHARDT, C.-Ueber die Bestimmung des Schmelz-punktes der Fette.

Zeit. f. an. Chem., Bd., xxv., 1886.

SKALWEIT, J.-Butter-Testing. Analyst, 1886, 90.

WEST-KNIGHT, E.-On the Estimation of the Insoluble Fatty Acids in Butter-Fat. Analyst, 1880, 155.

WIGNER, G. W.-On Estimation of the Gravities of Fats.

35.

Analyst, 1, 1877.

-On Butter Analysis by Koettstorfer's Process. Analyst, 1879, 132. On Butter-Fat, and Ratio of Expansion by Heat. Analyst, 1879, 183. WILEY, H.-Butter and its Adulterations. U.S. Dep. of AgricultureChem. division. Bull., No. 13, 1887.

WOLL.-Beiträge zur Butter Analyse. Zeit. f. an. Chem., 1887, 28. WRIGHT, C. R. ALDER. -Animal and Vegetable Oils and Fats, Butter, and Waxes. Lond. 1894.

ZUNE.--Traité général d'analyse des beurres. 2 vols. Paris et Bruxelles,

1892.

BUTTERMILK.

§ 187. Buttermilk is the thin whey left behind when the fat has been extracted in the process of butter-making. It is never fat-free; it contains all the constituents of milk, but a great portion of the sugar has been changed into lactic acid. then essentially a dilute, poor acid milk.

The average composition of fresh buttermilk is :—

It is

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The lactic acid tends ever to increase, so that samples which have stood a little time will contain more lactic acid than the proportion above given; besides the ordinary salts of milk it frequently contains the common salt added to preserve the butter. It is not an article of commerce, and from its occurrence merely as a bye-product differs in composition considerably.*

*Some analyses by Dr. Vieth (Analyst, 1884) may be thus summarised:

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