Part 42

If the proteid matters contain salts of ammonium it is probable that a difficultly soluble double sulfate of zinc and ammonium, (NH₄)₂SO₄.ZnSO₄.6H₂O, will be found in the precipitate. Ammonium salts, if present, should therefore be removed by distillation with magnesia. It is better, however, to throw down the ammonia with the first zinc precipitate, distil this with magnesia and determine the amount of nitrogen derived from the ammonia compounds. In a second sample, the total nitrogen is determined by moist combustion and the difference between the two results gives that due to albumoses.

=419. Examination for Muscular Tissue.=—Some samples of meat extracts contain small quantities of finely ground muscular tissue. For detecting this the extract is treated with cold water and the insoluble residue examined with a microscope. If muscular tissue be found, about eight grams of the extract or twenty-five of the fluid preparation, are treated with cold water, the insoluble matter collected upon a filter, washed with cold water, and the nitrogen determined in the residue. The percentage of nitrogen multiplied by 6.25 gives the quantity of muscle fiber proteids present. The filtrate from the above determination is acidified with acetic, boiled, any precipitate which is formed collected and the nitrogen therein determined. The nitrogen obtained multiplied by 6.25 gives the quantity of coagulable albumin present. An aliquot portion of the filtrate is used for the determination of nitrogen and the percentage therein found, deducted from the total nitrogen of the sample, gives a remainder which may be used as a representative of the whole of the nitrogen present in the form of albumin and muscular tissue.

=420. Estimation of Gelatin.=—The tin foil dish and its contents used for the determination of water, as above described, are cut into small pieces, placed in a beaker and extracted four times with absolute alcohol. After the removal of the alcohol, the residue is extracted with ice water containing ten per cent of alcohol, in which a small piece of ice is kept to avoid a rise of temperature. The beaker should be shaken during the extraction, which should last for about two minutes. Where large numbers of samples are treated at once, any convenient form of shaking machine may be employed. At least two extractions with ice water must be made. The residue is then collected upon a filter and washed with ice water until the washings are completely colorless. The residue on the filter is replaced in the beaker, boiled with water, well washed on the filter with boiling water, the filtrate and washings concentrated and the nitrogen therein determined.

The principle of this determination is based on the fact that gelatin is almost completely insoluble in ice water while serum peptones and albumin peptones are almost completely soluble in that reagent. On the other hand, the flesh bases and the proteids present are almost completely removed by the preliminary treatment with alcohol and ice water or are left undissolved by the hot water. The solution in boiling water, therefore, contains practically nothing but gelatin.[397]

In a later article, Stutzer modifies the method given above as follows:[398]

Of dry and moist extracts from five to seven grams and of liquid extracts from twenty to twenty-five grams are used for the determination and placed in tin foil dishes, as described above. In case of solid extracts, a sufficient quantity of warm water is added to completely dissolve them, the solution being facilitated by stirring. In case the solution is too thin it should be concentrated before going further. It is treated with a sufficient amount of dust-free ignited sand to completely absorb it, and the dish and its contents are then dried to a constant weight. The dried contents of the dish are rubbed up in a mortar, the dish cut into fine bits, and all placed in a beaker. The solid syrphete[399] is extracted four times with 100 cubic centimeters of absolute alcohol, the alcohol in each case being poured through an asbestos filter for the purpose of collecting any matters suspended therein. In a large flask are placed 100 grams of alcohol, 300 grams of ice and 600 grams of cold water, and the flask is placed in a large vessel and packed with finely divided ice. Four beakers marked _b, c, d, e_ are also placed in ice and the beaker containing the syrphete, left after extraction with absolute alcohol as above mentioned, is marked _a_ and also placed in pounded ice. The extraction with cold alcoholic water proceeds as follows:

In beaker _a_ are poured 100 cubic centimeters of the mixture in the large flask, its contents are stirred for two minutes and then the liquid portion poured off into beaker _b_ to which, at the same time, a piece of ice is added. In beaker _a_ are poured again 100 cubic centimeters from the large flask, treated as above described, and the liquid extract poured into beaker _c_. In like manner the extraction in beaker _a_ is continued until each of the beakers has received its portion of the extract. By this time the liquid over the sand in beaker _a_ should be completely colorless. The filtration of the liquid extract is accomplished as follows:

In a funnel of about seven centimeters diameter is placed a perforated porcelain plate about four centimeters in diameter which is covered with asbestos felt with long fiber. Three filters are prepared in this way. On the first filter are poured the contents of beaker _b_. After the liquid has passed through, the sand and other residue in beaker _a_ are transferred to the filter and the beaker and residue washed with the alcoholic ice water from the large flask. The filtration should be accomplished under pressure. On the second filter are poured the contents of beaker _c_. On the third filter the contents of beakers _d_ and _e_. The washing with alcoholic ice water from the large flask is continued in each instance until the filtrate is colorless. At the same time the asbestos filter, which was used in the first instance for filtering the absolute alcohol extract, is washed with the alcoholic ice water mixture from the large flask. At the end the sand remaining in beaker a together with all the asbestos filters are brought together into a porcelain dish, boiled two or three times with water, the aqueous solution filtered and the filtrate concentrated and used for the estimation of the nitrogen. The quantity of nitrogen found multiplied by 6.25 represents the proteid matter in the gelatin of the sample.

The object of the multiple filters, described above, is to accelerate the process, and they are required because the gelatin quickly occludes the filter pores. For this reason the asbestos filters are found to operate better than those made of paper. It should be mentioned that the residue of the peptones insoluble in alcohol may contain, in addition to gelatin, also small quantities of albumoses. From the quantity of albumose nitrogen found, it is understood that the nitrogen in the form of coagulable albumin, determined as described in the first process mentioned above, is to be deducted, since these coagulable albumins are insoluble in alcohol.

=421. Estimation of Nitrogen in the Flesh Bases Soluble in Alcohol.=—About five grams of the dry extract, ten grams of the extract containing water or twenty-five grams of the liquid extract are placed in a beaker and enough water added in each case to make about twenty-five cubic centimeters in all. Usually no water need be added to the liquid extracts. Very thin peptone solutions should be evaporated until the content of water is reduced to seventy-five per cent. The solution, prepared as above indicated, is treated slowly with constant stirring with 250 cubic centimeters of absolute alcohol, the stirring continued for some minutes and the vessel set aside for twelve hours, at the end of which time the precipitate is separated by filtration and washed repeatedly with strong alcohol. Leucin, tyrosin and a part of the flesh bases are dissolved by alcohol. The alcohol is removed by distillation and the residue dissolved in water. Any flocky residue which remains on solution with water is removed by filtration, the nitrogen determined therein and the quantity thereof added to the albumose nitrogen found, as hereafter described.

The volume of the aqueous solution is completed with water to half a liter. One hundred cubic centimeters of this solution are used for the determination of total nitrogen, and another 100 cubic centimeters for the determination of ammoniacal nitrogen by distillation with barium carbonate. A part of the ammonia may have escaped during the preliminary distillation of the alcohol and therefore the amount found may not represent the whole amount originally present. The use of the above determination is principally to ascertain the correction to be made in the amount of total nitrogen found in the first 100 cubic centimeters of the solution.

=422. Treatment of the Residue Insoluble in Alcohol.=—The residue insoluble in alcohol is washed from the filter into the beaker in which the first solution was made. The aqueous mixture is warmed on a water-bath until the alcohol adhering to the precipitate is completely evaporated, when the contents of the beaker are poured upon a filter free of nitrogen. A small part of the albumose, by reason of the treatment with alcohol, tends to remain undissolved, and it is advisable to collect this albumose upon a filter, wash it well with hot water and estimate the nitrogen therein. The quantity of nitrogen thus found is to be added to the albumose nitrogen determined as described later on.

The total filtrate obtained from the last filtration is made up to a volume of half a liter, of which fifty cubic centimeters are used for the determination of total nitrogen, fifty cubic centimeters for the determination of gelatin, albumose and peptone, and 100 cubic centimeters for the residual peptones. The albumose, together with the gelatin and peptones carried down with it, is precipitated with zinc or ammonium sulfate solution, and its per cent calculated from the amount of nitrogen found in the precipitate. The true peptone is determined by subtracting the quantity of nitrogen determined as albumose from the total nitrogen in solution.

The rest of the liquid, _viz._, 300 cubic centimeters, is evaporated to a small volume and tested qualitively for true peptones as follows:

To separate the albumose and gelatin a concentrated liquor is treated with an excess of finely divided ammonium sulfate so that a part of the salt remains undissolved. The separated albumose, gelatin and undissolved ammonium salts are collected on a filter, the filtrate mixed with a few drops of dilute copper sulfate solution and a considerable quantity of concentrated soda or potash lye added. Care should be taken that the quantity of copper is not too great, otherwise the peculiar red coloration will be obscured by the blue color of the copper solution.

=423. Pancreas Peptone.=—The filtrate obtained as described above, by treating the portion of the material insoluble in alcohol with warm water, contains in addition to the albumose and gelatin the whole of the pancreas peptone which may be present. To separate this peptone, 100 cubic centimeters of the aqueous solution are evaporated in a porcelain dish until the volume does not exceed ten cubic centimeters. When cool, at least 100 cubic centimeters of a saturated cooled solution of ammonium sulfate solution are added, the mixture thoroughly stirred, the precipitate collected upon a filter and washed with a cold saturated solution of ammonium sulfate. The contents of the filter are dissolved in boiling water, the filter thoroughly washed and the filtrate and washings evaporated in a porcelain dish with the addition of barium carbonate until, on the addition of new quantities of barium carbonate, no further trace of ammonia can be discovered. The residue is extracted with water, the barium sulfate and carbonate present separated by filtration, well washed and the nitrogen determined in the evaporated filtrate and washings in the usual way and multiplied by 6.25 to determine the quantity of pancreas peptone.

=424. Albumose Peptone.=—A part of the albumose peptone which may be present is determined in conjunction with the other bodies mentioned above. The chief quantity is found in the solution of the residue insoluble in alcohol in the following manner:

Fifty cubic centimeters of the solution of this residue in hot water are mixed with an equal volume of dilute sulfuric acid, one volume of acid to three of water, in the cold, and a solution of sodium phosphotungstate added until it produces no further precipitate. The precipitate is washed with dilute sulfuric acid and the nitrogen determined therein. The nitrogen thus found is derived from the albumose, pancreas peptone and gelatin. The quantity of nitrogen in the pancreas peptone and gelatin, as above described, is subtracted from the total quantity found in the phosphotungstic acid precipitated, and the remainder represents the nitrogen due to the albumose.

=425. Nitrogen in the Form of Flesh Bases Insoluble in Alcohol.=—This is determined by subtracting the quantity of nitrogen, determined by the phosphotungstic acid method already described, from the total quantity of nitrogen found in the precipitate insoluble in alcohol and soluble in water.

AUTHORITIES CITED IN PART FIFTH.

[337] Watts’ Dictionary of Chemistry, new edition, Vol. 4, p. 327.

[338] Vid. op. cit. supra, p. 330.

[339] Barbieri, Journal für praktische Chemie, neue Folge Band 18, S. 114.

[340] Vid. op. cit. 1, p. 339.

[341] Bulletin No. 49, Kansas Experiment Station, May, 1895.

[342] This work, Vol. 2, p. 208.

[343] Vid. op. cit. supra, Vol. 1, p. 570.

[344] Wiley, American Chemical Journal, Vol. 6, No. 5, p. 289.

[345] Obermayer, Chemiker-Zeitung Repertorium, Oct. 1889, S. 269.

[346] Hoppe-Seyler, Handbuch der physiologisch- und pathologisch-chemischen Analyse, S. 269.

[347] Wiley, American Chemical Journal, Vol. 6, p. 289.

[348] Dragendorff’s Plant Analysis, p. 55.

[349] This work, Vol. 2, pp. 192 et seq.

[350] Chemiker-Zeitung, Band 20, S. 151.

[351] This work, Vol. 2, p. 207.

[352] Landwirtschaftlichen Versuchs-Stationen, Band 17, S. 321: Zeitschrift für analytische Chemie, Band 14, S. 380.

[353] Vid. op. cit. 12, p. 245.

[354] Landwirtschaftlichen Versuchs-Stationen, Band 16, S. 61.

[355] Berichte der deutschen chemischen Gesellschaft, Band 10, Ss. 85, 199; Band 16, S. 312: Chemiker-Zeitung, Band 20, S. 145.

[356] Zeitschrift für analytische Chemie, Band 22, S. 325.

[357] Richardson and Crampton, Berichte der deutschen chemischen Gesellschaft, Band 19, S. 1180.

[358] Maxwell, American Chemical Journal, Vol. 13, p. 470.

[359] Vid. op. cit. supra, Vol. 15, p. 185.

[360] Vid. op. cit. supra, Vol. 13, p. 13: Schulze, Zeitschrift physiologische Chemie, Band 14, S. 491.

[361] This work, Vol. I, p. 411.

[362] Vid. op. cit., 22, Vol. 13, p. 15.

[363] Vid. op. cit. supra, Vol. 15, p. 188.

[364] Hoppe-Seyler, Handbuch der physiologisch- und pathologisch-chemischen Analyse, S. 169.

[365] This work, Vol. 2, p. 225.

[366] Bulletin No. 45, Division of Chemistry, U. S. Department of Agriculture, p. 51.

[367] Osborne and Voorhees, American Chemical Journal, Vol. 15, p. 470.

[368] Vid. op. cit. supra, Vol. 13, p. 385.

[369] Vid. op. cit. supra, p. 412.

[370] Vid. op. cit. supra, Vol. 15, p. 402.

[371] Vid. op. cit. supra, p. 404.

[372] Zeitschrift für analytische Chemie, Band 34, S. 562.

[373] Vid. op. cit. 34, p. 404.

[374] Vid. op. cit. 3, p. 455.

[375] Osborne and Voorhees, vid. op. cit. 34, p. 409.

[376] Vid. op. cit. supra, Vol. 13, p. 464.

[377] Chittenden and Osborne, op. cit. supra, Vol. 14, p. 32.

[378] Vid. op. cit. supra, p. 41.

[379] Vid. op. cit. supra, p. 639.

[380] Vid. op. cit. supra, Vol. 13, p. 399.

[381] Vid. op. cit. supra, pp. 395, 400, 401.

[382] Vid. op. cit. supra, p. 409.

[383] This work, Vol. 1, p. 319.

[384] This work, Vol. 2, pp. 169 et seq.

[385] Vid. op. cit. 47, p. 420.

[386] Osborne, vid. op. cit. 44, p. 410.

[387] Hoppe-Seyler, Handbuch der physiologisch- und pathologisch-chemischen Analyse.

[388] König und Bömer, Zeitschrift für analytische Chemie, Band 34, S. 560.

[389] This work, Vol. 2, pp. 297, 298.

[390] Vid. op. cit. supra, p. 184.

[391] Vid. op. cit. supra, p. 206.

[392] This work, Vol. I, p. 450; Vol. 2, p. 226.

[393] Zeitschrift für analytische Chemie, Band 34, S. 377.

[394] König und Bömer, vid. op. cit. supra, S. 560.

[395] Vid. op. cit. supra, S. 562.

[396] Vid. op. cit. 53, p. 184.

[397] Vid. op. cit. 57, S. 374.

[398] Vid. op. cit. supra, S. 568.

[399] From συρφετος.

PART SIXTH.

DAIRY PRODUCTS.

=426. Introductory.=—The importance of dairy products has led to the publication of a vast amount of literature relating thereto, and it seems almost a hopeless task to present even a typical abstract of the various analytical processes which have been proposed and used in their study. The general principles which have been developed in the preceding parts of this volume are applicable to the study of dairy products, and the analyst who is guided by them can intelligently examine the bodies specially considered in the present part. There have been developed, however, many valuable processes for the special examination of dairy products, which are of such a nature that they could not be properly discussed in the preceding pages. In the present part an effort will be made to present in a typical form the most important of these processes and to state the general principles on which they are based. This subject is naturally subdivided into three parts, _viz._, milk, butter and cheese. The milk sugar industry is not of sufficient importance to receive a special classification.

MILK.

=427. Composition of Milk.=—The composition of milk not only varies with the genus and species of the mammal from which it is derived, but also depends in a marked degree on idiosyncrasy.[400]

Milk is a mixture containing water, proteids, fat, carbohydrates, organic and inorganic acids and mineral salts. There have also been observed in milk in minute quantities ammonia, urea, hypoxanthin, chyme, chyle, biliverdin, cholesterin, mucin, lecithin, kreatin, leucin and tyrosin. In the fermentation which milk undergoes in incipient decomposition there is sometimes developed from the proteid matter, as pointed out by Vaughn, a ptomaine, tyrotoxicon, which is a virulent poison.[401] The presence of these last named bodies is of interest chiefly to the physiologist and pathologist and can receive no further attention here.

From a nutritive point of view, the important components of milk are the fats, proteids and sugar, but especially in the nourishment of the young the value of lime and phosphoric acid must be remembered. The mean composition of the most important milks, as determined by recent analyses, is given below:

Water. Sugar. Proteids. Fat. Ash. Per cent. Per cent. Per cent. Per cent. Per cent. Cow 86.90 4.80 3.60 4.00 0.70 Human 88.75 6.00 1.50 3.45 0.30 Goat 85.70 4.45 4.30 4.75 0.80 Ass 89.50 6.25 2.00 1.75 0.50 Mare 90.75 5.70 2.00 1.20 0.35 Sheep 80.80 4.90 6.55 6.85 0.90

The mean composition of milk, as given by Watts and König, is given in the following tables:

WATTS. Mineral Water. Solids. Proteids. Fats. Sugar. Salts. Woman 87.65 12.35 3.07 3.91 5.01 0.17 Ass 90.70 9.30 1.70 1.55 5.80 0.50 Cow 86.56 13.44 4.08 4.03 4.60 0.73 Goat 86.76 13.24 4.23 4.48 3.91 0.62 Sheep 83.31 16.69 5.73 6.05 3.96 0.68 Mare 82.84 17.16 1.64 6.87 8.65

KÖNIG. Casein and Milk Water. Fat. albumin. sugar. Ash. Woman 87.41 3.78 2.29 6.21 0.31 Mare 90.78 1.21 1.99 5.67 0.35 Ass 89.64 1.63 2.22 5.99 0.51 Cow 87.17 3.69 3.55 4.88 0.71

The average composition of 120,540 samples of cow milk, as determined by analysis, extending over a period of eleven years, was found by Vieth to be as follows:[402]

Per cent. Total solids 12.9 Solids not fat 8.8 Fat 4.1

The quantity of solids and fat in milk is less after longer than after shorter periods between milkings.

The quantity of solids and fat in cow milk is less in the spring than in the autumn.

The chief organic acid naturally present in milk is citric, which exists probably in combination with lime.

The mean content of citric acid in milk is about one-tenth of one per cent.[403]

Citric acid is not found in human milk, and probably exists only in the mammary secretions of herbivores.

Among the mineral acids of milk, phosphoric is the most important, but a part of the phosphorus found as phosphoric acid in the ash of milk may come from pre-existing organic phosphorus (lecithin, nuclein).

The sulfuric acid, which is found in the ash of milk, is derived from the sulfur of the proteid matter during ignition.

Lactic acid is developed from lactose during the souring of milk as the result of bacterial activity.

Gases are also found in solutions of milk, notably carbon dioxid, which gives to freshly drawn milk its brothy appearance.

The ash of milk has the following composition expressed as grams per liter of the original milk:[404]

Grams Probable form Grams Component. per liter. of combination. per liter.

{ sodium chlorid 0.962 Chlorin 0.90 { potassium chlorid 0.830

{ KH₂PO₄ 1.156 { K₂HPO₄ 0.853 Phosphoric acid 2.42 { MgHPO₄ 0.336 { CaHPO₄ 0.671 { Ca₃(PO₄)₂ 0.806

Potassium 1.80 (as shown above) and as potassium citrate 0.495

Sodium 0.49 sodium chlorid 0.962

Lime 1.90 (as shown above) and as calcium citrate 2.133

Magnesia 0.20 MgHPO₄ 0.336

The percentage composition of the ash of milk, according to Fleischmann and Schrott, is expressed as follows:[405]

Per cent. Potassium oxid, K₂O 25.42 Sodium oxid, Na₂O 10.94 Calcium oxid, CaO 21.45 Magnesium oxid, MgO 2.54 Iron oxid, Fe₂O₃ 0.11 Sulfuric acid, SO₃ 4.11 Phosphoric acid, P₂O₅ 24.11 Chlorin, Cl 14.60 ------ 103.28 Less Cl as O 3.28 ------ 100.00