METHODS OF ANALYSIS AND THEIR DISCUSSION.

One of the great obstacles in the way of a thorough and careful study of proteids is the unsatisfactory condition of the analytical methods. Many of the variations in results which have appeared are undoubtedly due to faulty methods. Another serious source of error in this line of work lies in the fact that different methods are used by different analysts and the results are not comparable. For instance, copper oxid, phosphotungstic acid, tannic acid and salt, and other reagents, are used by various workers to precipitate the higher amido bodies and separate them from the simpler amido bodies. That the precipitating power of these reagents is not the same is well known. For determining acid and alkali albumins, insoluble proteid, and coagulable proteid, the methods give only approximate results, those for the determination of several of the individual bodies, such as kreatin, kreatinin, and ammonia, being in a much more satisfactory condition.

PREPARATION OF SAMPLE.

In the case of liquid and semiliquid preparations the bottle should be thoroughly shaken and great care taken to see that the solution is complete. Pasty and solid extracts or powders should be removed from the container and thoroughly mixed before sampling. A very convenient method is to dissolve a weighed sample in a measured quantity of water and run this out of a burette as needed. This solution should be kept cold and the determinations started without delay.

MOISTURE.

Moisture was determined in the various preparations examined by drying the sample over night in a water-jacketed drying oven. In the case of solid meat extracts approximately 3 grams of the sample were used, for fluid extracts, 10 to 12 grams, and for meat powders, 2 grams.

ASH.

The ash content of the commercial samples is seen to be surprisingly high in many cases. (See Tables II, IV, and IX.) This is due to the fact that sodium chlorid is present in meat extracts in varying and often excessive quantities. Especial attention is called to the large percentage of sodium chlorid present in several of the samples examined. The figures reported in the tables are obtained by calculating the total chlorin to sodium chlorid.

The ash was determined by the official method and the sodium chlorid in the ash by the following procedure:

Dissolve the ash sample with nitric acid and make up to volume in a 200-ce flask. Use 20 per cent, or any convenient aliquot, for titration with sulpho-cyanid according to the Volhard method.

a

@ U. S. Dept. Agr., Bureau of Chemistry, Bul. 107, p. 38.

A small amount of sodium chlorid is present in meat, and as much as 12 per cent is permitted by the tentative standard for meat extract, but the presence of 25 to 30 per cent is excessive and should be regarded as an adulteration.

From 0.8 to 1.8 per cent of meat is mineral matter, and calculated to water-free substance this amounts to from 2.3 to 7.5 per cent. The average composition of the ash of meat, according to König," is as follows:

Jolly gives some very interesting figures showing the various combinations of phosphoric acid found in the muscles and tendons of calves and oxen, and the metabolism of the various mineral salts is fully discussed by Albu and Neuberg. The analyses of the ash of several samples of meat juice prepared in the laboratory are given in Table XI.

The most striking point in the analysis of the ash of meat extracts is the large amount of potash salts present, practically one-half of the salt-free (NaCl-free) ash being composed of potassium oxid. The amount of phosphoric acid is also high, amounting to fully one-third of the salt-free ash. The percentage of phosphoric acid given in the table may be low, as part of the organic phosphoric acid is volatile especially if the ash be heated to a very high temperature. The other constituents of the ash of meat juice are oxid of iron, a Chemische Zusammensetzung der menschlichen Nahrungs- und Genussmittel. 1889. 3rd ed., 1: 236.

Compt. rend., 1879, 89:958.

Mineral Stoffwechsel, Berlin, 1906.

The provisional volumetric method was used-U. S. Dept. Agr., Bureau of Chemistry, Bul. 107, p. 16.

calcium, magnesium, and sodium. Phosphates and sulphates of calcium and potassium, organic sulphur, and a small amount of insoluble matter, principally silica, are also present.

In Table XII figures are given showing the composition of the ash of various meat extracts and miscellaneous preparations. As the percentage of sodium chlorid shown in Table XII is much greater than that present in the natural meat juice, the figures for the salt-free ash are correspondingly lower. The amount of insoluble matter is surprisingly high in several cases and it appears that some insoluble substance must have been added. For comparison the following results are quoted from König," showing the average composition of the ash of meat extracts:

Results of the analysis of the ash of meat peptones are also given. König states that the salts, especially the potash salts present in the ash of meat extracts, are valuable on account of their action on the nervous system.

TABLE XII.—Analyses of the ash of meat extracts and miscellaneous preparations.