TABLE 4. Cooperative work on the determination of melting point on mixtures prepared by Determination of melting point on a series of mixtures containing graded proportions of oleo stearin added to the same lard. The results given above show clearly that the figure 71 for the sum A +2 (A-B) is too low to provide against quite material adulterations. The examination of the samples of pure lard shows that this figure may be increased to 73 without danger of condemning pure lard. It is recommended therefore that the method be adopted as a tentative method in the following form: METHOD FOR THE DETECTION OF ADULTERATION OF LARD WITH FATS CONTAINING TRISTEARIN. Weigh out 5 grams of the filtered fat into a glass-stoppered cylinder graduated to 25 cc., add warm acetone until the 25 cc. mark is reached. Shake the cylinder until the contents are thoroughly mixed; then allow the cylinder and its contents to stand in a suitable place in which a temperature of 30°C. is maintained. After 18 hours, remove the cylinder and carefully decant the supernatant acetone solution from the crystallized glycerides, which are usually found in a firm mass at the bottom of the cylinder. Then add warm acetone in three portions of 5 cc. each from a small wash bottle, care being taken not to break up the deposit while washing and decanting the first two portions. Actively agitate the third portion in the cylinder and, by a quick movement, transfer with the crystals to a small filter paper. Wash the crystals with five successive small portions of the warm acetone by means of the wash bottle and remove by suction the excess acetone. Transfer the paper with its contents to a suitable place, where it should be spread out, and any large lumps of the glycerides broken up by gentle pressure. When dry, thoroughly comminute the mass and determine the melting point of the crystals'. A melting point below 63.0 is regarded as evidence of adulteration, and a melting point below 63.4 is regarded as suspicious. After the melting point of the crystallized glycerides has been determined, transfer them to a 50 cc. beaker, add 25 cc. of approximately N/2 alcoholic potassium hydroxid and heat on the steam bath until saponification is complete. Pour the solution into a separatory funnel containing 200 cc. of distilled water, acidify, add 75 cc. of ether and shake. Draw off the acid layer and wash at least three times with distilled water. Transfer the ether solution to a clean, dry 50 cc. beaker, drive off the ether on the steam bath and finally dry the acids at 100°C. After the acids have stood for at least 2 hours after drying, determine the melting point in the same manner in which the melting point of the crystals was determined. If the melting point of the glycerides plus twice the difference between the melting point of the glycerides and the melting point of the fatty acids is less than 73°C., the lard is regarded as adulterated. REPORT ON DAIRY PRODUCTS. By JULIUS HORTVET (State Dairy and Food Commission, St. Paul, Minn.), Referee. The work included: (1) A further study of modifications of the official Roese-Gottlieb method applied to malted milk, dried milk and plain ice cream. (2) A further study of the Harding-Parkin method for fat determinations in comparison with the present official and provisional methods. (3) A further study of the tentative Schmidt-Bondzynski modified method for the determination of fat in cheese. In accordance with the plan of work above outlined, the instructions sent out to the collaborators included full descriptions of the methods, following in the main the original published authors' texts or the texts as found in the last compilation of tentative and official methods of analysis2. No material changes were incorporated and such additional directions as seemed to be required were given in separate paragraphs. Directions were given regarding the preparation, weighing, and preliminary treatment of samples. Much attention has been given by the referee to these preliminary details and experience has led to the conclusion that no uniform rule of procedure can be laid down which will be suitable for all classes of dairy products. Before the application of 1 U. S. Bur. Animal Ind. Circ. 132: (1908). 2 Assoc. Official Agr. Chemists, Methods, 1916, 287. the regular analytical method, therefore, it has been found necessary to subject each given sample to such mode of preliminary treatment as has been shown by experience to yield most reliable results. The collaborators were also given general instructions relative to the following topics: (a) the condition of the sample as to fitness for analysis; (b) the various comparative tests to be made on each sample submitted; (c) the number of determinations to be made in duplicate and the averages to be reported; (d) the importance of experience and preliminary trials of the various methods before attempting determinations for the purposes of collaborative work. In the 1916 report of the referee1, considerable attention was given to a discussion of the acid extraction modification of the official Roese-Gottlieb procedure, and it was then recommended that this modification be given further study. Accordingly, the plan of work has been so arranged as to secure from the collaborators comparative results showing the relative merits of the two procedures which have been somewhat in controversy for many years. Whatever may be the relative theoretical advantages of either mode of treatment of material before proceeding with the extractions, the aim has been at least to obtain practical comparative results under as favorable uniform conditions as possible by as many analysts as could be engaged to assist in the work. The referee is indebted to W. D. Strack, Chief Chemist for Borden's Condensed Milk Company, New York, N. Y., for obtaining uniform sets of samples and forwarding them direct to the collaborators. Each set of samples included: (1) a plain ice cream, preserved with 15 grains of mercuric chlorid, in a tightly covered glass container; (2) a dried skimmed milk enclosed in a pasteboard carton; (3) a malted milk powder in a well-sealed bottle. In the study of the modified Schmidt-Bondzynski method, each collaborator was provided with a sample of Parmesan, a type of Italian cheese made from partly skimmed milk. Also, several weeks later, uniform samples of an American Pineapple cheese were distributed, and, although this type of cheese is essentially a Cheddar cheese made from whole milk, there was little difficulty experienced in preparing uniform samples and getting them to the collaborators in condition satisfactory for analysis. The collaborators were directed to carry out the work described in the following instructions: 1 J. Assoc. Official Agr. Chemists, 1920, 3: 436. PREPARATION OF SAMPLES. DRIED MILK AND MALTED MILK. Thoroughly mix the entire sample before weighing a portion for analysis. Weigh out a 1 gram sample and transfer to the Röhrig tube with the help of a camel's hair brush and glazed paper. The mixing and weighing should be done as rapidly as possible for the reason that these powders very readily take up moisture from the air. (a) Alkaline method.-Add 10 cc. of water to the sample in the Röhrig tube, place the tube in a water bath at 60°C. and mix the contents by frequent shaking until no lumps remain. Add 2 cc. of concentrated ammonium hydroxid, mix thoroughly, heat again in the water bath at 60°C., and proceed as directed in the official Roese-Gottlieb method. (b) Acid method. Heat the sample with 10 cc. of hydrochloric acid (sp. gr. 1.125) in the Röhrig tube, by means of a water bath at 80°C. for 15-25 minutes, being certain that the curd is well dissolved. Cool, add 10 cc. of alcohol, and proceed as in the official Roese-Gottlieb method. ICE CREAM. Allow the sample to soften at room temperature. Stir thoroughly with a spoon or mix by pouring from one beaker to another. Another good method of obtaining a uniform sample is to mix with an egg beater just before weighing. Owing to the fact that melted butter fat readily separates out and tends to rise to the surface, it is not advisable to soften the ice cream by heating on a water bath or over a flame. Weigh out 4 grams of the sample in a small dry beaker, add 3 cc. of water, thoroughly mix with a glass rod, and pour into the Röhrig tube, washing out the remaining portion with 3 cc. of water. Add 2 cc. of concentrated ammonium hydroxid, mix thoroughly, heat in a water bath at 60°C., and proceed as directed in the official Roese-Gottlieb method. The method of weighing may be simplified by pouring the mixed sample into a 25 cc. graduated cylinder. Weigh the cylinder, pour about the right amount into a tube, weigh, and determine the amount of the sample by difference. CHEESE. By means of a cheese sampler, draw three plugs, one from the center, one from a point near the outer edge, and one from a point between the other two. Reject the rind and grind the plugs in a sausage machine or cut them very finely and mix thoroughly. Proceed as directed in the Schmidt-Bondzynski method. DESCRIPTION OF METHODS. ROESE-GOTTLIEB METHOD.-OFFICIAL1. Notes on the method.-If an emulsion occurs in the Röhrig tube, the addition of a little alcohol, followed by shaking, will usually break it up. Also, the use of a tube having a larger caliber will tend to overcome this difficulty. If a Röhrig tube is not available, prepare an apparatus consisting of a large test tube provided with a blow-off device, as used in the Werner-Schmidt method. Care should be taken to make the final weighing of the ether-freed residue of fat under exactly the same conditions as those under which the dish was first weighed. 1 Assoc. Official Agr. Chemists, Methods, 1916, 289. |