Chapter XXI: Preface: To Volume Third (21)

When the reichert-meissl number falls below twenty-five the sample may be regarded with suspicion. The detection of the characteristic crystals of lard or tallow is reliable corroborating evidence (=308=).

It is stated by Kühn[525] that the margarin factory of Mohr, at Bahrenfeld-Altona, has made for many years a perfect emulsion of fat with skim milk. This product has been much used in the manufacture of filled cheese which is often found upon the German market.

=516. Separation of the Nitrogenous Bodies in Cheese.=—The general methods of separation already described for proteid bodies (=417-425=) are also applicable to the different nitrogenous bodies present in cheese, representing the residue of these bodies as originally occurring in the milk, and also the products which are formed therefrom during the period of ripening. For practical dietary and analytical purposes, these bodies may be considered in three groups:

(_a_) The useless (from a nutrient point of view) nitrogenous bodies, including ammonia, nitric acid, the phenylamido-propionic acids, tyrosin, leucin and other amid bodies.

(_b_) The albumoses and peptones, products of fermentation soluble in boiling water.

(_c_) The caseins and albuminates, insoluble in boiling water.

The group of bodies under (_a_), according to Stutzer, may be separated from the groups (_b_) and (_c_) by means of phosphotungstic acid. For this purpose a portion of an intimate mixture of fine sand and cheese (100 cheese, 400 sand) corresponding to five grams of cheese, is shaken for fifteen minutes with 150 cubic centimeters of water. After remaining at rest for another fifteen minutes 100 cubic centimeters of dilute sulfuric acid (one acid, three water) are added, followed by treatment with the phosphotungstic acid as long as any precipitate is produced. The mixture is thrown on a filter and the insoluble matters washed with dilute sulfuric acid until the filtrate amounts to half a liter. Of this quantity an aliquot part (200 cubic centimeters) is used for the determination of nitrogen. From the quantity of nitrogen found, that representing the ammonia, as determined in a separate portion, is deducted and the remainder represents the nitrogen present in the cheese as amids.[526]

_Albumoses and Peptones._—Albumoses and peptones are determined in cheese by the following method:[527] A quantity of the sand mixture already described, corresponding to five grams of the cheese, is treated with about 100 cubic centimeters of water, heated to boiling, and the clear liquid above the sand poured into a flask of half a liter capacity. The extraction is continued with successive portions of water in like manner until the volume of the extract is nearly half a liter. When cold, the volume of the extract is completed to half a liter with water, the liquor filtered, 200 cubic centimeters of the filtrate treated with an equal volume of dilute sulfuric acid (one to three) and phosphotungstic acid added until no further precipitate takes place. The nitrogen is determined in the precipitate after filtration and washing with dilute sulfuric acid.

_Casein and Albuminates._—The quantity of casein and albuminates in cheese is calculated by subtracting from the total nitrogen that corresponding to ammonia, amids, that in the indigestible residue and that corresponding to the albumose and peptone. In three samples of cheese, _viz._, camembert, swiss, and gervais, Stutzer found the nitrogen, determined as above, distributed as follows:[528]

Camembert. Swiss. Gervais.
N as ammonia 13.0 3.7 1.6
N as amids 38.5 9.0 5.2
N as albumose peptone 30.5 8.6 15.5
N indigestible 4.0 2.4 8.6
N as casein, albuminates 14.0 76.3 69.1

_Ammoniacal Nitrogen._—The ammoniacal nitrogen is determined by mixing a quantity of the sand-cheese corresponding to five grams of cheese, with 200 cubic centimeters of water, adding an excess of barium carbonate and collecting the ammonia by distillation in the usual way.

_Digestible Proteids._—The digestible proteids in cheese are determined by the process of artificial digestion, which will be described in the part of this volume treating of the nutritive value of foods.

These data show the remarkable changes which the proteids undergo where the ripening is carried very far as in the camembert cheese.

=517. Koumiss.=—Fermented mare milk has long been a favorite beverage in the East, where it is known as koumiss. In Europe and this country cow milk is employed in the manufacture of fermented milk, although it is less rich in lactose than mare milk. The process of manufacture is simple, provided a suitable starter is at hand. A portion of a previous brewing is the most convenient one, the fermentation being promoted by the addition of a little yeast. After the process of fermentation is finished the koumiss is placed in bottles and preserved in a horizontal position in a cellar, where the temperature is not allowed to rise above 12°.

=518. Determination of Carbon Dioxid.=—The carbon dioxid in koumiss is conveniently estimated by connecting the bottle by means of a champagne tap with a system of absorption bulbs.[529] The exit tube from the koumiss bottle passes first into an erlenmeyer, which serves to break and retain any bubbles that pass over. The water is next removed by means of sulfuric acid. The koumiss bottle is placed in a bath of water which is raised to the boiling point as the evolution of the gas is accomplished. The arrangement of the apparatus is shown in Fig. 113. At the end of the operation any residual carbon dioxid in the apparatus is removed by aspiration after removing the tap and connecting it with a soda-lime tube to hold the carbon dioxid in the air. A large balance suited to weighing the koumiss bottle is required for this determination. The carbon dioxid may also be determined, but less accurately, by loss of weight in the koumiss bottle after adding weight of water retained in the apparatus.

=519. Acidity.=—Although koumiss may contain a trace of acetic acid, it is best to determine the acid as lactic. The clarification is most easily accomplished by mixing the koumiss with an equal volume of ninety-five per cent alcohol, shaking and filtering. The first filtrate will usually be found clear. If not it is refiltered. In an aliquot part of the filtrate the acidity is determined by titration with tenth-normal sodium hydroxid solution, using phenolphthalein as indicator. The necessary corrections for dilution and volume of the precipitated casein are to be made. A linen filter may be used when paper is found too slow.

=520. Alcohol.=—Half a liter of koumiss, to which 100 cubic centimeters of water have been added, is distilled until the distillate amounts to 500 cubic centimeters.

If the distillate be turbid 100 cubic centimeters of water are added and the distillation repeated. The alcohol is determined by the processes described hereafter.

=521. Lactose.=—The milk sugar may be determined by any of the methods described, but most conveniently by double dilution and polarization (=86=).

=522. Fat.=—Evaporate twenty grams of the sample to dryness and extract with pure ether or petroleum spirit in the manner already described (=455=).

The analysis is more quickly accomplished by the volumetric method of Babcock or Gerber (=473-475=).

=523. Proteids.=—The total proteids are most easily estimated by the official kjeldahl method.[530] The separation of the proteid bodies is accomplished by the methods described in paragraphs =475-489=.

In addition to the methods already described for separating the soluble and suspended proteid bodies in milk, and which may be used also for koumiss, the following should also be mentioned as of especial worth:

_Separation by Filtration through Porous Porcelain._—A purely physical method, and one which is to be recommended by reason of the absence of any chemical action upon the different proteid matters, is that proposed by Lehmann, depending upon the principle that when milk is forced through porous porcelain, the albumin passes through together with the milk, sugar and other soluble constituents as a clear filtrate, while the casein and fat are perfectly retained.[531]

By this method it is quite certain that the albumin and other perfectly soluble proteids of milk may be obtained in the purest form.

_Separation by Precipitation with Alum._—Probably the best chemical method of separating the two classes of proteid matters is that proposed by Schlosmann, which is effected by means of precipitating the casein with a solution of alum.[532]

The principle of this separation rests upon the fact that a solution of potash alum, when added to milk diluted with four or five times its volume of water, will completely separate the casein without affecting the albumin or globulin. The operation is conducted as follows:

Ten cubic centimeters of the milk are diluted with from three to five times that quantity of water and warmed to a temperature of about 40°. One cubic centimeter of a concentrated solution of potash alum is added, the mixture well stirred and the coagula which are formed allowed to subside. If the coagulation of the casein does not take place promptly, a small addition of the alum solution is made, usually not exceeding half a cubic centimeter, until the precipitation is complete. The temperature during the process should be kept as nearly as possible 40°. After a few minutes, the mixture is poured upon a filter and the filtrate, if not perfectly clear, is poured back until it is secured free of turbidity. In difficult cases the filtration may be promoted by the addition of some common salt or calcium phosphate, the latter acting mechanically in holding back the fine particles of casein. The precipitate is washed with water at a temperature of 40°, and afterwards with alcohol, not allowing the alcohol wash water to flow into the filtrate. When the water has been chiefly removed from the precipitate by washing with alcohol, the fat of the precipitated casein is removed with ether and the residue used for the determination of nitrogen in the usual way. The albumin is removed from the filtrate by a tannin solution in the manner already described (=480=). If it be desired to separate the albumin and globulin, the methods described in paragraph =399= may be used.

=524. Mercurial Method.=—A volumetric method for determining the total proteid matter in milk has lately been proposed by Deniges.[533] It is based upon the observation that in the precipitation of proteid matter by mercury salts, a definite quantity of mercury in proportion to the amount of proteid, is carried down therewith. The precipitation is made with a mercurial salt of known strength and the excess of the mercurial salt in the filtrate is determined by titration. For the details of the manipulation, the paper cited above may be consulted.

=525. Water and Ash.=—From two to five grams of the koumiss are dried to constant weight in a flat platinum dish over ignited sand, asbestos or pumice stone, and the dried residue incinerated.

=526. Composition of Koumiss.=—The composition of koumiss varies with the character of the milk used and the extent of the fermentation. Some of the data obtained by analysts are given below:[534]

COMPOSITION OF KOUMISS.

Carbon
Kind Water, Sugar, Alcohol, Fat, Proteid, dioxid, Acidity,
of Per Per Per Per Per Per Per
milk. cent. cent. cent cent. cent. cent. cent.
Cow 89.32 4.38 0.76 2.08 2.56 0.83 0.47
Probably 3.95 1.38 0.88 2.89 0.82
cow
skim’d
Mare 91.87 0.79 2.89 1.19 1.91 1.04

From the above it is seen that koumiss is made either from whole or skim milk, and that the percentage of alcohol may vary within large limits, its proportion being inverse to that of the milk sugar.

Koumiss is a beverage which is very palatable, easily digested and one which is not appreciated in this country in proportion to its merits, especially for the use of invalids.

AUTHORITIES CITED IN PART SIXTH.

[400] Wiley; Proceedings of the Society for the Promotion of Agricultural Science, 1889, p. 84. (Omit “food” before idiosyncrasy.)

[401] Pharmaceutical Journal and Transactions, Series 3, Vol. 18, p. 479.

[402] The Analyst, 1892, p. 85.

[403] Henkel; Wiener Landwirtschaftliche Zeitung, 1888, S. 401: Bulletin No. 24, Division of Chemistry, U. S. Department of Agriculture, p. 155.

[404] Die Landwirtschaftlichen Versuchs-Stationen, Band 35, S. 351: Bulletin No. 24, Division of Chemistry, U. S. Department of Agriculture, p. 151.

[405] Baumeister; Milch und Molkerei-Producte, S. 16.

[406] Bulletins Nos. 9 and 25 of the Office of Experiment Stations, U. S. Department of Agriculture: Farmers’ Bulletins Nos. 9 and 29, U. S. Department of Agriculture.

[407] Annales de Chimie et de Physique, 3e Série, Tome 64, p. 61.

[408] Bulletin de la Société Chimique de Paris, 3ᵉ Série, Tome 15-16, p. 248.

[409] Vid. op. cit. supra, p. 453.

[410] Central-Blatt für medicinische Wissenschaft, Band 34, S. 145.

[411] Conn; Farmers’ Bulletins 9 and 25, Office of Experiment Stations, U. S. Department of Agriculture: Farmers’ Bulletins 9 and 29, Department of Agriculture: Les Microbes et leur Rôle dans la Laiterie Freudenreich: Langlois, Le Lait, pp. 95 et seq.

[412] The Analyst, Vol. 20, p. 157.

[413] Vid. op. cit. supra, p. 152.

[414] Forschungs-Berichte über Lebensmittel etc., Band 2, S. 368.

[415] Vid. op. cit. supra, Band 1, S. 422.

[416] Vid. op. cit. supra, S. 372.

[417] Hopkins and Powers; Bulletin No. 47, Division of Chemistry, U. S. Department of Agriculture, p. 127.

[418] Bulletin No. 38, Division of Chemistry, U. S. Department of Agriculture, p. 118.

[419] Becke; Die Milchprüfungs-Methoden, S. 45: Rouvier; Le Lait, p. 45.

[420] The Analyst, 1890, Vol. 16, p. 170.

[421] Rouvier; Le Lait, p. 35.

[422] Central-Blatt für Nahrungs und Genussmittel Chemie, Band 13, S. 277.

[423] Bulletin No. 46, Division of Chemistry, U. S. Department of Agriculture, p. 36.

[424] Journal für Landwirtschaft, 1882, S. 293; 1885, S. 251.

[425] Vid. op. cit. supra, 1879, S. 249.

[426] Forschungen auf dem Gebiete der Viehhaltung, 1879, S. 265.

[427] The Analyst, Vol. 7, p. 129.

[428] Vid. op. cit. supra, Vol. 13, p. 26.

[429] Bulletin No. 47, Division of Chemistry, U. S. Department of Agriculture, p. 123.

[430] This work, Vol. 1, page 411.

[431] Bulletin No. 16, Division of Chemistry, U. S. Department of Agriculture, p. 36.

[432] Sixth Annual Report Wisconsin Agricultural Experiment Station, p. 64.

[433] Fourth Annual Report New York (Geneva) Agricultural Experiment Station, p. 298.

[434] Woll; Seventh Annual Report Wisconsin Agricultural Experiment Station, p. 238.

[435] The Analyst, 1885, p. 46: Bulletin No. 13, Part 1, Division of Chemistry, U. S. Department of Agriculture, p. 86.

[436] Haidlen; Die Milchprüfungs-Methoden, S. 12.

[437] Dingler’s polytechnisches Journal, Band 232, S. 461.

[438] Macfarlane; The Analyst, Vol. 18, p. 73.

[439] Duclaux; Le Lait, p. 176.

[440] Abraham; The Analyst, Vol. 9, p. 22.

[441] Gantter; Zeitschrift für analytische Chemie, Band 26, S. 677.

[442] Morse, Piggot and Burton; American Chemical Journal, Vol. 9, pp. 108 and 222.

[443] Chemiker-Zeitung Repertorium, 1889, S. 228.

[444] Journal de Pharmacie et de Chimie, 1890, p. 460.

[445] Richmond; The Analyst, Vol. 17, p. 48: Bulletins 28, 31, 35, 38, 43, and 46, Division of Chemistry, U. S. Department of Agriculture.

[446] Bulletin No. 28, Division of Chemistry, U. S. Department of Agriculture, p. 31.

[447] Zeitschrift für analytische Chemie, Band 27, S. 464.

[448] Chemical News, Nov. 1889.

[449] The Analyst, Vol. 16, p. 67.

[450] Vid. op. cit. supra, Vol. 18, p. 53.

[451] Vid. op. cit. supra, Vol. 17, p. 81.

[452] Chemiker-Zeitung, Band 15, S. 1833.

[453] Journal of Analytical Chemistry, 1888, Vol. 2, p. 371: Fifth Annual Report Wisconsin Agricultural Experiment Station.

[454] Molkerei Zeitung, 1892, No. 1; Chemisches Central-Blatt, 1892, Band 2, S. 429.

[455] Chemiker-Zeitung, Band 18, S. 1816; Band 19, S. 348.

[456] Zeitschrift für analytische Chemie, Band 32, S. 168.

[457] Zeitschrift des Landwirtschaftlichen Vereins in Bayern, 1880; Zeitschrift für analytische Chemie, Band 20, S. 452.

[458] Bulletin No. 13, Division of Chemistry, U. S. Department of Agriculture, p. 92.

[459] Instruction sur l’Emploi du Lactobutyrometer, Paris, 1856 et 1878: Becke; Die Milchprüfungs-Methoden, S. 66.

[460] Bulletin No. 8, Iowa Agricultural Experiment Station, p. 295.

[461] Dingler’s polytechnisches Journal, Band 261, S. 219.

[462] Milch Zeitung, Band 21, S. 496.

[463] Op. cit. supra, Band 22, S. 85.

[464] Bulletin No. 24, Wisconsin Agricultural Experiment Station.

[465] Bulletin No. 31, Wisconsin Agricultural Experiment Station.

[466] The Analyst, Vol. 17, p. 83.

[467] Bulletin No. 21, Vermont Agricultural Experiment Station.

[468] Vid. op. cit. 67, Vol. 17, p. 144; Vol. 18, p. 130; Vol. 19, p. 62.

[469] Chemiker-Zeitung, Band 16, S. 1839.

[470] Vid. op. cit. supra, Band 19, S. 348; Band 18, S. 1816.

[471] Vid. op. cit. supra, Band 19, S. 348.

[472] Comptes rendus, Tome 107, p. 772; Hoppe-Seyler’s Handbuch der Physiologisch- und Pathologisch-Chemischen Analyse, S. 479.

[473] Proceedings of the Society for the Promotion of Agricultural Science, 1888, p. 13.

[474] Journal of Physiology, Vol. 11, p. 459.

[475] Die Land wirtschaftlichen Versuchs-Stationen, Band 31, S. 131.

[476] Sixth Annual Report of the Wisconsin Agricultural Experiment Station, p. 64.

[477] Bulletin No. 46, Division of Chemistry, U. S. Department of Agriculture, p. 36.

[478] Zeitschrift für Biologie, Band 33, S. 43.

[479] Journal für praktische Chemie, {2}, Band 15, S. 329.

[480] Vid. op. cit. 79, Band 33, {Neue Folge, 15}, S. 55.

[481] Stenberg; Zeitschrift für physiologische Chemie, Band 13, S. 138.

[482] Vid. op. cit. supra, S. 137.

[483] Vid. op. cit. supra, S. 160.

[484] Journal of the American Chemical Society, Vol. 15, p. 644.

[485] Handbuch der Physiologisch- und Pathologisch-Chemischen Analyse, S. 285. (Read, Makris instead of Makeris.)

[486] Zeitschrift für Biologie, Band 23, S. 64.

[487] Bulletin de la Société Chimique de Paris, 3ᵉ Série, Tome 11, p. 152.

[488] Vid. op. cit. 86, S. 487.

[489] Zeitschrift für Nahrungsmittel-Untersuchung, Band 10, S. 104.

[490] Zeitschrift für physiologische Chemie, Band 9, S. 445.

[491] American Chemical Journal, Vol. 6, p. 289.

[492] Journal of the American Chemical Society, Vol. 18, p. 428.

[493] Journal de Pharmacie et de Chimie, 6e Série, Tome 4, p. 65.

[494] Contribution à l’Étude des Lactoses, Thèse pour le diplôme supérieure de Pharmacie, Paris, 1892. (Read Thibault instead of Thibonet.)

[495] Journal für praktische Chemie, Neue Folge, Band 15, S. 348.

[496] Zeitschrift für angewandte Chemie, 1896, S. 72.

[497] Chemisches Central-Blatt, 1892, Band 2, S. 1028.

[498] Vid. op. cit. supra, Band 21, S. 753.

[499] Vid. op. cit. 90, S. 86.

[500] Bulletin No. 13, Division of Chemistry, U. S. Department of Agriculture, pp. 29 et seq.

[501] Vid. op. cit. supra, pp. 73-75: Bulletin No. 46, Division of Chemistry, U. S. Department of Agriculture, p. 26.

[502] Benedikt and Lewkowitsch; Oils, Fats and Waxes, p. 490.

[503] Forsuchungs-Berichte über Lebensmittel, 1895, Band 2, S. 424; Chemiker-Zeitung Repertorium, 1896, Band 20, S. 15.

[504] Revue Internationale des Falsifications, Mai, 1893, p. 157.

[505] Chemiker-Zeitung, 1893, Band 17, S. 468.

[506] Zeitschrift für angewandte Chemie, 1896, S. 177.

[507] Vid. op. cit. 90, Aug. 26, 1894, S. 219; Le Stazioni Sperimentali Agrarie Italiane, 1893, pp. 25-77.

[508] Farmers’ Bulletin No. 12, U. S. Department of Agriculture.

[509] Bulletin de l’Association Belge des Chimistes, Tome 9, p. 279.

[510] Vid. op. cit. 101, p. 26.

[511] Vid. op. cit. supra, p. 27: Chemical News, Vol. 55, p. 49.

[512] Vid. op. cit. 111, p. 28.

[513] Vid. op. et. loc. cit. supra.

[514] Russell; Dairy Bacteriology.

[515] Woll; Dairy Calendar, p. 223.

[516] Van Slyke; Bulletin 82, New Series, New York Agricultural Experiment Station, p. 654.

[517] Babcock; Twelfth Annual Report Wisconsin Agricultural Experiment Station, p. 133.

[518] Woll; Dairy Calendar, 1895, p. 220.

[519] Bulletin No. 46, Division of Chemistry, U. S. Department of Agriculture, p. 37.

[520] Landwirtschaftliches Jahrbuch, 1872, part 1.

[521] Molkerei Zeitung, 1893, Nos. 20, 22.

[522] This work, Vol. 2, p. 204.

[523] Vid. op. cit. 120, p. 24.

[524] Milch Zeitung, 1895, Band 24, S. 729: Chemiker-Zeitung Repertorium, Band 19, S. 372.

[525] Chemiker-Zeitung, 1895, S. 554.

[526] Zeitschrift für analytische Chemie, Band 35, S. 497.

[527] Vid. op. cit. supra, S. 499.

[528] Vid. op. cit. supra, S. 502.

[529] Bulletin No. 13, Division of Chemistry, U. S. Department of Agriculture, pp. 118, 293.

[530] This work, Vol. 2, p. 204.

[531] Pflüger’s Archiv, Band 56, S. 558.

[532] Hoppe-Seyler’s Zeitschrift für physiologische Chemie, Band 22, S. 213.

[533] Bulletin de la Société Chimique de Paris, Tomes 15-16, p. 1126.

[534] American Chemical Journal, Vol. 8, p. 200: Bulletin 13, Division of Chemistry, U. S. Department of Agriculture, p. 120.

PART SEVENTH.

MISCELLANEOUS AGRICULTURAL PRODUCTS.

=527. Classification.=—In the preceding parts have been set forth the fundamental principles underlying the conduct of agricultural analysis and a résumé of the best practice of the art. The analyst, as a rule, will seldom be required to undertake investigations which are unnoticed in the preceding pages. Cases will arise, however, in which problems are presented which can not be solved by the rules already elucidated. In respect of the great classes of agricultural bodies, it will be observed that dairy products have already received special mention. In respect of foods and fodders in general, it is evident that they are chiefly composed of moisture, ash, carbohydrates, oils and proteid matters. The methods of identifying, separating and estimating these constituents have been fully set forth. It is not necessary, therefore, to study in this part the analytical processes which are applicable to cereals, cattle foods and other food products, further than is necessary to present in the most important cases a working résumé of principles and methods. There remain, however, certain products of importance which require some special modifications of treatment, and it is to these that the present part will be chiefly devoted. Among these are found tobacco, tea and coffee, fruits, fermented and distilled drinks and certain animal products. It is evident that an enumeration of all agricultural products, with a description of their methods of examination, would be impracticable in the available space and undesirable by reason of the repetition which would be required. In each case the analyst, in possession of the methods described, will be able to adapt the means at his disposal to the desired purpose to better advantage than any rigid directions could possibly secure.

In respect of the analytical methods of determining the nutritive value of foods, they may be divided into chemical and physiological. The chemical methods embrace the thermal and artificial digestion investigations, and the physiological include those which are carried out with the help of the animal organisms. In the latter case the digestive process is checked by the analysis of the foods before ingestion and of the excreta of all kinds during and after digestion.

It is evident that a detailed description of this method should be looked for in works devoted to physiological chemistry.

CEREALS AND CEREAL FOODS.

=528. General Analysis.=—The cereals are prepared for analysis by grinding until the fragments pass a sieve having circular perforations half a millimeter in diameter. The moisture, ash, ether extract, proteids and carbohydrates are determined by some one of the processes already described in detail. In this country the methods of the Association of Official Agricultural Chemists are generally followed.[535] For convenience these methods are summarized below.

_Moisture._—Dry from two to three grams of the fine-ground sample for five hours, at the temperature of boiling water, in a current of dry hydrogen. If the substance be held in a glass vessel, the latter should not be in contact with the boiling water.

_Ash._—Char from two to three grams of the sample and burn to whiteness at the lowest possible red heat. If a white ash can not be obtained in this manner, exhaust the charred mass with water, collect the insoluble residue on a filter, burn it, add this ash to the residue from the evaporation of the aqueous extract and heat the whole to low redness until the ash is white.

_Ether Extract._—Pure ether is prepared by washing the commercial article four or five times with water to free it of the chief part of the alcohol it contains. The residual water is mostly removed by treating the liquid with caustic soda or potash. Any residual alcohol or water is finally removed by the action of metallic sodium. The ether thus prepared is stoppered, after the evolution of hydrogen has ceased, and is kept over metallic sodium. Immediately before use it should be distilled out of contact with moist air.

The residue from the determination of moisture, as described above, is extracted in an appropriate apparatus (=39=) with the pure ether for sixteen hours. The extract is dried to constant weight. The weight may be checked by drying and weighing the extraction tube and its contents before and after the operation.

_Crude Proteids._—Proceed as in the method of determining nitrogen in the absence of nitrates and multiply the weight of nitrogen obtained by 6.25. This factor is a general one, but should not be rigidly applied. In each instance, according to the nature of the cereal, the appropriate factor, pointed out in paragraph =407= should be used, and the factor 6.25 be applied only in those cases where a special factor is not given. The factors for the common cereals are wheat 5.70, rye 5.62, oats 6.06, maize 6.22, barley 5.82 and flaxseed 5.62.

For separating the proteid matters consult paragraphs =392-410=. In the case of wheat the methods of Teller may be consulted.[536]

_Amid Nitrogen._—The albuminoid nitrogen is determined as directed in paragraph =203= of volume II. The difference between this number and that representing the total nitrogen gives the nitrogen as amids.

_Fiber and Carbohydrates._—The methods of analysis are described in detail in Part Third.

=529. Bread.=—In general, the same processes are followed in bread analysis as are used with cereals and flours. In addition to the regular analytical processes, breads are to be examined for adulterants, bleaching and coloring matters, and for the purpose of determining the changes which have taken place in their nutrient constituents in the processes of fermentation and cooking.

_Temperature of Baking._—The interior of a loaf during the process of baking does not attain the high temperature commonly supposed. This temperature is rarely found to be more than one degree above the boiling point of water.[537] In biscuits and other thin cakes, which become practically dry and which by reason of their thinness are the more readily penetrated by heat, the temperature may go as high as 110°.

_Soluble Extract._—The quantity of matters both in flour and bread, soluble in cold water, is determined by extraction in the usual way and drying the extract. Soluble albuminoids, sugars and mineral salts are extracted by this process. When possible, the operation should be conducted both on the bread and the flour from which it is made.

_Color._—In baker’s parlance is found an apparent contradiction of terms, since it speaks of bread with “no color” when the loaf is dark brown, while a white loaf is said to have a high color. An ideal color for the interior of a loaf is a light cream tint, which is more desirable than a pure white.[538] The texture, odor and flavor of the loaf are also to be considered, but these are properties of more importance to the technical expert than to the analyst.

_Quantity of Water._—It is not possible to set a rule of limitation in respect of the quantity of water a bread should hold. For full loaves, perhaps forty per cent is not too high a maximum, while some authors put it as low as thirty-four per cent. Some flours are capable of holding more water than others, and the loaf should have just enough water to impart to the slice of bread the requisite degree of softness and the proper texture. Most breads will have a content of water ranging from thirty to forty per cent. In biscuits and other thin cakes the moisture is much less in quantity.

_Acidity._—The acidity of both bread and flour is determined by shaking ten grams of the sample with 200 cubic centimeters of distilled water for fifteen minutes, pouring the mass on a filter and titrating an aliquot part of the filtrate with tenth-normal alkali. The acidity is reckoned as lactic acid in the case of breads raised by fermentation.

_Nature of Nitrogenous Compounds._—The methods of investigation are described in paragraphs =392-410=.

=530. Determination of Alum in Bread.=—The presence of alum in bread may be detected by means of logwood. Five grams of fresh logwood chips are digested with 100 cubic centimeters of amyl alcohol. One cubic centimeter of this decoction and the same quantity of a saturated solution of ammonium carbonate are mixed with ten grams of flour and an equal quantity of water. With pure flour, a slight pink tint is produced. In the presence of alum the color changes to a lavender or blue, which is persistent on heating.

The test may be varied by diluting five cubic centimeters of the reagents mentioned with ninety cubic centimeters of water and pouring the mixture over ten grams of the crumbled bread. After standing for five minutes, any residual liquid is poured off and the residue, washed once with a little water, is dried in a steam bath, when the blue color is developed if alum be present.[539]

=531. Chemical Changes Produced by Baking.=—Changes of a chemical nature, produced in bread by baking, are found chiefly in modifications of the starch and proteids. The starch is partly converted into dextrin and the albumins are coagulated. The changes in digestion coefficient are determined by the methods which follow. The fermentations which precede the baking are due to the usual decompositions of the carbohydrates under the influence of yeast germs.

FODDERS, GRASSES AND ENSILAGE.

=532. General Principles.=—The analyst, in examining the fibrous foods of cattle, is expected to determine moisture, ash, fiber and other carbohydrates, ether extract and albuminoid and amid nitrogen. If a more exhaustive study be required, the sugar and starch are separated from the other non-nitrogenous matters, the carbohydrate bodies yielding furfuraldehyd separately determined and the ash subjected to a quantitive analysis. The processes are conducted in harmony with the principles and methods of procedure fully set forth in the preceding pages.

Green fodders and grasses are easily dried and sampled by comminution in the shredder described on page 9, and roots by that shown on page 10. The moisture is determined by drying a small sample of the shredded mass, while the rest of it is dried, first at about 60° and finally at 100°, or a little above, ground to a fine powder and subjected to analysis by methods already described. The food values as obtained by analysis should be compared, when possible, with those secured by natural and artificial digestion.

Ensilage is shredded and analyzed in precisely the same way, but in drying, the content of volatile acids formed during fermentation must be considered. In other words, the loss on drying ensilage at 100°, or slightly above, is due not only to the escape of water but also to the volatilization of the acetic acid, which is one of the final products of fermentation which the mass undergoes in the silo.

=533. Organic Acids in Ensilage.=—In the examination of ensilage, the organic acids which are present may be determined by the processes described in following paragraphs. The acetic acid, formed chiefly by fermentation, is conveniently determined by the method given for tobacco further on. Lactic acid is detected and estimated by expressing the juice from a sample of ensilage, removing the acetic acid by distillation, repeated once or twice, and treating the filtered residue with zinc carbonate in excess, filtering and determining the zinc lactate in the filtrate. The zinc is determined by the method described for evaporated apples and the lactic acid calculated from the weight of zinc found. Crystallized zinc lactate contains 18.18 per cent of water and 27.27 per cent of zinc oxid.[540]

=534. Changes due to Fermentation in the Silo.=—Silage differs from green fodder in having less starch and sugar, more acetic and lactic acids and alcohol and a higher proportion of amid to albuminoid nitrogen.[541] There is also a considerable loss of nitrogenous substances in ensilage, due probably to their conversion into ammonium acetate, which is lost on drying.

=535. Alcohol in Ensilage.=—The fermentation which takes place in the silo is not wholly of an alcoholic nature, as the development of lactic acid, noted above, clearly indicates. The alcohol which is formed may escape and but small quantities can be detected in the ripened product. So small is this quantity of alcohol that it appears to be useless to try to secure a quantitive estimation of it. Qualitively, it may be detected by collecting it in a distillate, which is neutralized or made slightly alkaline with soda or potash lye and redistilled. The greater part of the alcohol will be found in the first few cubic centimeters, which are made alkaline with potash lye and as much iodin added as can be without giving a red tint to the solution. Any alcohol which is present will soon separate as iodoform.

=536. Comparative Values of Fodder and Ensilage.=—In judging of the comparative values of green and dry fodders for feeding purposes, it is necessary to secure representative samples in the green, quickly dried and ensilaged condition. It is quite certain that the greater part of the sugar contained in green fodders is lost both by natural curing and by placing in a silo. When well cured by the usual processes there is but little loss of nitrogenous matters, but in the silo this loss is of considerable magnitude, amounting in some instances to as much as thirty per cent.

The ideal way of preparing green fodders in order to preserve the maximum food value efficiently, is to shred them and dry rapidly by artificial heat, or in the sunlight, until they are in a condition which insures freedom from fermentation. In this condition, when placed in bales, under heavy pressure, the food constituents are preserved in the highest available form. The immense sugar content of the stalks of maize and sorghum could be preserved in this way almost indefinitely.

FLESH PRODUCTS.

=537. Names Of Meats.=—The parts of the animal from which the meats are taken have received distinctive names, which serve to designate the parts of the carcass offered for sale. These names are not invariable and naturally are quite different in many markets. In this country there is some degree of uniformity among butchers in naming the meats from different parts. The names in scientific use for the parts of mutton, beef and pork are found in the accompanying illustrations.[542]

=538. Sampling.=—When possible the whole animal should constitute the sample. The relative weights of blood, intestinal organs, hide, hoofs, horns, bones and edible flesh are determined as accurately as possible. The general method of preparing samples of animal products is given in paragraph =5=.

The method of sampling employed by Atwater and Woods is essentially that just noted.[543] The sample, as received at the laboratory, is weighed, the flesh (edible portion) is then separated from the refuse (skin, bones etc.) and both portions weighed. There is always a slight loss in the separation, evidently due to evaporation and to small fragments of the tissues that adhere to the hands and to the implements used in preparing the sample. The perfect separation of the flesh from the other tissues is difficult, but the loss resulting from this is small. In sampling the material for analysis, it is finely chopped, either in a tray or in a sausage cutter, and in each case is well mixed.

=539. Methods of Analysis.=—The general methods for the analyses of food products are applicable to meats and animal products in general. In the separation of the nitrogenous constituents the methods described in paragraphs =411-414= are followed. It is not safe to estimate as proteids the total nitrogen multiplied by 6.25, since the flesh bases have much higher percentages of nitrogen than are found in proteid matters. As indicated in paragraph =280= the complete extraction of dried meats by ether is difficult of accomplishment. After a few hours it may be assumed that the total extract will represent the fat, although additional soluble matters are obtained by continuing the process. The heat producing power may be calculated from the analytical data secured. The methods which have been described in the preceding pages will be found sufficient for guidance in the examination of animal products, and the analyst will find them, when modified to suit particular cases, adapted to the isolation and estimation of proximate food principles.

The methods of analyses followed by Atwater and Woods are given below:[544]

_Water and Water-Free Substance._—The drying is done in ordinary water ovens at a temperature of nominally 100°, but actually at 96° and 98°. For each analysis of animal tissues (flesh) one or more samples of from fifty to one hundred grams of the freshly chopped substance are weighed on a small plate, heated for from twenty-four to forty-eight hours, cooled, allowed to stand in the open air for about twenty-four hours, weighed, ground, sifted through a sieve with circular holes one-half millimeter in diameter, bottled and set aside for analysis. In case of fat samples which cannot be worked through so fine a sieve, either a coarser sieve is used or the substance crushed as finely as practicable and bottled without sifting.

For the complete desiccation, about two grams of material are dried for three hours. It is extremely difficult to get an absolutely constant weight, though it is found that this is in most cases approximately attained in four hours.

_Nitrogen, Protein, Albuminoids etc._—The nitrogen is determined in the partly dried substance by the method of Kjeldahl. The protein is calculated by multiplying the percentage of nitrogen by 6.25. The nitrogenous matters in meats and fish, _i. e._, in the materials which have practically no carbohydrates, are also estimated by subtracting the sum of ether extract and ash from the water-free substance, or the sum of water, ether extract and ash from the fresh substance, the remainder being taken as proteids, albuminoids etc., by difference. While this is not an absolutely correct measure of the total nitrogenous matter, it is doubtless more nearly so than the product of the nitrogen multiplied by 6.25.

_Fat (Ether Extract)._—The fat is extracted with ether in the usual manner. The point at which the extraction is complete is not always easy to determine. For the most part, the extraction is continued for such time as experience indicates to be sufficient, and then the flask is replaced by another and the extraction repeated until the new flask shows no increase in weight.

According to experience, the fat of many animal tissues is much more difficult to extract than that of most vegetable substances. In general, the greater the percentage of fat in a substance the more difficult is the removal of the last traces. Dried flesh is frequently so hard that the fineness of the material to be extracted seems to be a very important matter.

_Ash._—Ash is determined by the method recommended by the Association of Official Agricultural Chemists.

_Food Value—Potential Energy._—The food materials are not necessarily burned in the calorimeter, but the fuel value of a pound of each of the foods, as given in the tables, is obtained by multiplying the number of hundredths of a pound of protein and of carbohydrates by 18.6 and the number of hundredths of a pound of fat by 42.2, and taking the sum of these three products as the number of calories of potential energy in the materials.

More reliable results are obtained by using the factors obtained by Stohmann; _viz._, 5731 calories for proteids, 9500 calories for common glycerids, 9231 calories for butter fat, 3746 calories for pentose sugars, 3749 calories for dextrose and levulose and 3953 calories for sucrose and milk sugar.[545]

=540. Further Examination of Nitrogenous Bodies.=—It is evident that both of the methods proposed above for the examination of the nitrogenous constituents of meats are unreliable. If the total nitrogen be determined and multiplied by 6.25 the product does not by any means represent the true quantity of nitrogenous matter since the flesh bases contain in some instances more than twenty-five per cent of nitrogen.

If, on the other hand, the water, ash and fat in a meat sample be determined and the sum of their per cents be subtracted from 100, the difference represents the nitrogenous bodies plus all undetermined matters and errors of analysis. The assumption that meats are free of carbohydrates is not tenable since glycogen is constantly found therein and in horse flesh in comparatively large amounts. In a thoroughly scientific analysis of meats, the nitrogenous bodies should be separated and determined by groups, according to the principles developed in paragraphs =411-414=. This process requires a great amount of analytical work and in general it will be sufficient to make a cold water extract to secure the flesh bases and a hot water extract to secure the gelatin. The nitrogen is then determined in each of these portions separately. The nitrogen in the cold water extract is multiplied by four, in the hot water extract by six and in the residue by 6.25. The sum of these products represents approximately the total nitrogenous matter in the sample.

Aqueous extracts containing nitrogen are easily prepared for moist combustion by placing them in the digestion flasks, connecting the latter with the vacuum service and evaporating the contents of the flask nearly to dryness. The sulfuric acid is then added and the nitrogen converted into ammonia and determined in the usual manner.

=541. Fractional Analysis of Meats.=—A better idea of the composition of a meat is obtained by separating its constituents into several groups by the action of different solvents. This method has been elaborated by Knorr.[546]

The separation of the meats in edible portion and waste and the determination of moisture and fat are conducted as already described. The residue from the fat extraction is exhausted with alcohol, and in the extract are found the nitrogenous bases kreatin, kreatinin, sarkin and xanthin, and urea, lactic, butyric, acetic and formic acids, glycogen and inosit. In the residue from the alcohol extraction, the proteid nitrogen is determined in a separate sample.

A separate portion of the sample is ground to a fine paste and repeatedly rubbed up with cold water, which is poured through a tared filter. When the extraction is complete, the filter and its contents are dried and the dry residue determined. This residue represents the nitrogenous constituents of the muscle fibers and their sheaths together with any other bodies insoluble in cold water. The filtrate from the cold water extraction is heated to boiling to precipitate the albuminous matters which are collected, dried and weighed, or the nitrogen therein determined and the albuminous matters calculated by multiplying by the usual factor. The filtrate from the coagulated albuminous bodies is evaporated to dryness and weighed. It consists essentially of the same materials as the alcoholic extract mentioned above. The ash and nitrogen in the aqueous extract are also determined.

The mean content of the edible parts of common meats, expressed as per cents in groups as mentioned, follow:

Per cent.
Water 73.11
Ash 1.18
Total soluble matter 26.89
Phosphoric acid 0.49

Per cent.
{ Proteids insoluble in cold water 13.76
{ Of which coagulable by heat 2.24
Cold water extract 3.56
{ Ash in water extract 1.09
{ Of which phosphoric acid 0.38

Per cent.
Fat 4.93
Alcohol extract 3.03
Proteids in residue from alcohol 17.88
Total nitrogen in sample 3.37

=542. Estimation of Starch in Sausages.=—Starchy substances are sometimes added to sausages for the purpose of increasing their weight. The presence of starch in a sausage is easily detected by iodin. The quantity may be determined by the following process:[547]

The principle of the process is based upon the observation that while starch is easily soluble in an aqueous solution of the alkalies, it is insoluble in an alcoholic solution thereof. The chief constituents of meat, _viz._, fat and proteid matters, on the other hand, are readily soluble in an alcoholic solution of potash or soda. This renders the separation of the starch easy. The sample is warmed on a water bath with a considerable excess of an eight per cent solution of potassium hydroxid in alcohol whereby the fat and flesh are quickly dissolved. The starch and other carbohydrate bodies, remain in an undissolved state. In order to prevent the gelatinizing of the soap which is formed, the mass is diluted with warm alcohol, the insoluble residue collected upon a filter and washed with alcohol until the alkaline reaction disappears. The residue is then treated with aqueous potassium hydroxid solution, whereby the starch is brought into solution and, after filtration, is treated with alcohol until it is all precipitated. The precipitated starch is collected upon a filter, washed with alcohol and finally with ether, dried and weighed. Starch prepared in this way contains a considerable quantity of potash, the amount of which can be determined by incineration. In order to avoid this trouble, the starch, after separation in the first instance as above mentioned and solution in aqueous potassium hydroxid, is precipitated on the addition of enough acetic to render the solution slightly acid. The precipitated starch, in this instance, is practically free of potash, since potassium acetate is soluble in alcohol.

=543. Detection of Horse Flesh.=—Since horse flesh has become an important article of human food and is often sold as beef and sausage, a method of distinguishing it is desirable. The comparative anatomist is able to detect horse flesh when accompanied by its bones, or in portions sufficiently large for the identification of muscular characteristics. It is well known that horse flesh contains a much higher percentage of glycogen than is found in other edible meats. Niebel has based a method of detecting horse flesh upon this fact, the glycogen being converted into dextrose and determined in the usual way. Whenever the percentage of reducing sugars in the dry fat-free flesh exceeds one per cent, Niebel infers that the sample under examination is horse flesh.[548]

The reaction for horse flesh, proposed by Bräutigam and Edelmann, is preferred by Baumert. In this test about fifty grams of the flesh are boiled for an hour with 200 cubic centimeters of water, the filtered bouillon evaporated to about half its volume, treated with dilute nitric acid and the clear filtrate covered with iodin water. Horse flesh, by reason of its high glycogen content, produces a burgundy red zone at the points of contact of the two liquids. In the case of sausages, if starch have been added, a blue zone is produced, and if dextrin be present, a red zone, both of which obscure the glycogen reaction. The starch is easily removed by treating the bouillon with glacial acetic acid. No method is at present known for separating dextrin from glycogen. The detection of horse flesh is a matter of considerable importance to agriculture as well as to the consumers, especially of sausages. A considerable quantity of horse flesh is annually sent to the market, little of which presumably is sold under its own name. As a cheap substitute for beef and pork in sausages, its use must be regarded as fraudulent, although no objection can be urged against its sale when offered under its own name.[549]

METHODS OF DIGESTION.

=544. Artificial Digestion.=—The nutrient values of cereals and other foods are determined both by chemical analysis and by digestion experiments. The heat forming properties of foods are disclosed by combustion in a calorimeter, but the quantity of heat produced is not in every case a guide to the ascertainment of the nutritive value. This is more certainly shown, especially in the case of proteid bodies, by the action of the natural digestive ferments.

It is probable that the digestion, which is secured by the action of these ferments without the digestive organs, is not always the same as the natural process, but when the conditions which prevail in natural digestion are imitated as closely as possible the effects produced can be considered as approximately those of the alimentary canal in healthy action.

Three classes of ferments are active in artificial digestion, _viz._, amylolytic ferments, serving to hydrolyze starch and sugars and to convert them into dextrose, maltose and levulose, aliphalytic ferments, which decompose the glycerids and proteolytic ferments, which act on the nitrogenous constituents of foods. When these ferments are made to act on foods under proper conditions of acidity and temperature, artificial digestion ensues, and by the measurement of the extent of the action an approximate estimate of their digestibility can be secured. In artificial digestion, the temperature should be kept near that of the body, _viz._, at about 40°.

The soluble ferments which are active in the digestion of foods, as has been intimated, comprise three great classes. Among the first class, _viz._, the amylolytic ferments, are included not only those which convert starch into dextrose, but also those which cause the hydrolysis of sugars in general. Among these may be mentioned ptyalin, invertase, trehalase, maltase, lactase, diastase, inulase, pectase and cyto-hydrolytic ferments which act upon the celluloses and other fibers.

Among the aliphalytic ferments, in addition to those which act also upon proteid matter, may be mentioned a special one, lipase.

In the third class of ferments are found pepsin, trypsin or pancreatin and papain.

For the latest information in regard to the nature of the soluble ferments and their nomenclature, the work of Bourquelot may be consulted.[550]

=545. Amylytic Ferments.=—A very active ferment of this kind is found in the saliva. Saliva may be easily collected from school boys, who will be found willing to engage in its production if supplied with a chewing gum. A gum free of sugar is to be used, or if the chewing gum of commerce is employed, the saliva should not be collected until the sugar has disappeared. A dozen boys with vigorous chewing will soon provide a sufficient quantity of saliva for practical use. The amylolytic digestion is conducted in the apparatus hereinafter described for digestion with pepsin and pancreatin. The starch or sugar in fine powder is mixed with ten parts of water and one part of saliva and kept at about 37°.5 for a definite time. The product is then examined for starch, sucrose, maltose, dextrose, dextrin and levulose by the processes already described. In natural digestion the hydrolysis of the carbohydrates is not completed in the mouth. The action of the ferment is somewhat diminished in the stomach, but not perhaps until half an hour after eating. The dilute hydrochloric acid in the stomach, which accumulates some time after eating, is not active in this hydrolysis. On the contrary the amylolytic ferment of the saliva is somewhat enfeebled by the presence of an acid. The active principle of the saliva is ptyalin.

The diastatic hydrolysis of starch has already been described (=179=). It is best secured at a somewhat higher temperature than that of the human stomach.

=546. Aliphalytic Ferments.=—In the hydrolysis of glycerids in the process of digestion the fat acids and glycerol are set free. Whether the glycerids be completely hydrolyzed before absorption is not definitely known. In certain cases where large quantities of oil have been exhibited for remedial purposes, the fat acids and soaps have been found in spherical masses in the dejecta[551] and have been mistaken for gall stones.

The fat which enters the chyle appears to be mostly unchanged, except that it is emulsified.[552] The aliphalytic ferment can be prepared from the fresh pancreas, preferably from animals that have not been fed for forty hours before killing. It is important to prepare the ferment entirely free of any trace of acid. The fresh glands are rubbed to a fine paste with powdered glass and extracted for four days with pure glycerol, to which one part of one per cent soda solution has been added. The filtered liquor contains aliphalytic, proteolytic and amylytic ferments, and is employed for saponification by shaking with the fat to form an emulsion and keeping the mixture, with occasional shaking, at a temperature of from 40° to 60°. The free acids can be titrated or separated from the unsaponified fats by solution in alcohol.[553]

Heretofore it has not been possible to separate a pure aliphalytic ferment from any of the digestive glands. The digestion of carbohydrates and that of fats are intimately associated, and these two classes of foods seem to play nearly the same rôle in the animal economy.

The aliphalytic ferments, prepared from the fresh pancreas, act also on the glucosids and other ester-like carbohydrate bodies. Since the fats may be regarded as ethers, the double action indicates the similarity of composition in the two classes of bodies.[554] The aliphalytic ferments exist also in plants and have been isolated from rape seed.[555]