| Q = [Q] + | ( | H | - O | ) | 0.291. |
| 2 |
566. Calorimetric Equivalents.—By the term calorie is understood the quantity of heat required to raise one gram of water, at an initial temperature of about 18°, one degree. The term ‘Calorie’ denotes the quantity of heat, in like conditions, required to raise one kilogram of water one degree.
For purposes of comparison and for assisting the analyst in adjusting his apparatus so as to give reliable results, the following data, giving the calories of some common food materials, are given:
| Substance. Proteids. | Calories. | Chemical composition. | ||||
|---|---|---|---|---|---|---|
| C. | H. | N. | S. | O. | ||
| Per cent. | Per cent. | Per cent. | Per cent. | Per cent. | ||
| Serum albumin | 5917.8 | 53.93 | 7.65 | 15.15 | 1.18 | 22.09 |
| Casein | 5867.0 | 54.02 | 7.33 | 15.52 | 0.75 | 22.38 |
| Egg albumin | 5735.0 | 52.95 | 7.50 | 15.19 | 1.51 | 22.85 |
| Meat free of fat and | 5720.0 | 52.11 | 6.76 | 18.14 | 0.96 | 22.66 |
| extracted with water | ||||||
| Peptone | 5298.8 | 50.10 | 6.45 | 16.42 | 1.24 | 25.79 |
| Proteids (mean) Glycerids. | 5730.8 | 52.71 | 7.09 | 16.02 | 1.03 | 23.15 |
| Butterfat | 9231.3 | |||||
| Linseed oil | 9488.0 | |||||
| Olive oil | 9467.0 | |||||
| Carbohydrates. | Formula. | |||||
| Arabinose | 3722.0 | C₅H₁₀O₅ | ||||
| Xylose | 3746.0 | C₅H₁₀O₅ | ||||
| Dextrose | 3742.6 | C₆H₁₂O₆ | ||||
| Levulose | 3755.0 | C₆H₁₂O₆ | ||||
| Sucrose | 3955.2 | C₁₂H₂₂O₁₁ | ||||
| Lactose | 3736.8 | C₁₂H₂₂O₁₁ + H₂O | ||||
| Maltose | 3949.3 | C₁₂H₂₂O₁₁ | ||||
567. Distinction between Butter and Oleomargarin.—Theoretically the heats of combustion of butter fat and oleomargarin are different and de Schweinitz and Emery propose to utilize this difference for analytical purposes.[583] The samples of pure butter fat examined by them afforded 9320, 9327 and 9362 calories, respectively. The calories obtained for various samples of oleomargarin varied from 9574 to 9795. On mixing butter fat and oleomargarin, a progressive increase in calorimetric power is found, corresponding to the percentage of the latter constituent. Lards examined at the same time gave from 9503 to 9654 calories.
FRUITS, MELONS AND VEGETABLES.
568. Preparation of Sample.—Fresh fruits and vegetables are most easily prepared for analysis by passing them through the pulping machine described on [page 9]. Preliminary to the pulping they should be separated into skins, cores, seeds and edible portions, and the respective weights of these bodies noted. Each part is separately reduced to a pulp and, at once, a small quantity of the well mixed substance placed in a flat bottom dish and dried, first at a low temperature, and finally at 100°, or somewhat higher, and the percentage of water contained in the sample determined. The bulk of the sample, three or four kilograms, is dried on a tray of tinned or aluminum wire, first at a low and then at a high temperature, until all or nearly all the moisture is driven off. The dried pulp is then ground to as fine a powder as possible and subjected to the ordinary processes of analysis; viz., the determination of the moisture, ash, nitrogen, fiber, fat and carbohydrates.
In this method of analysis it is customary to determine the carbohydrates, exclusive of fiber, by subtracting the sum of the per cents of the other constituents and the nitrogen multiplied by 6.25 from 100.
569. Separation of the Carbohydrates.—It is often desirable to determine the relative proportions of the more important carbohydrates which are found in fruits and vegetables. The pentoses and pentosans are estimated by the method described in paragraph [150]. The cane sugar, dextrose and levulose are determined by extracting a portion of the substance with eighty per cent alcohol and estimating the reducing sugars in the extract before and after inversion by the processes described in paragraphs [238-251]. The percentages of sugars deducted from the percentage of carbohydrates, exclusive of fiber, give the quantity of gums, pentosans, cellulose and pectose bodies present.
Pectose exists chiefly in unripe fruits. By the action of the fruit acids and of a ferment, pectose, in the process of ripening, is changed into pectin and similar hydrolyzed bodies soluble in water. The gelatinous properties of boiled fruits and fruit juices are due to these bodies, boiling accelerating their formation. In very ripe fruits the pectin is completely transformed into pectic acids. The galactan is estimated as described in [585].