A manual of physics, theoretical and practical : for medical students / by Hugh C. H. Candy.

  • Candy, Hugh Charles Herbert, 1859-1935
Date:
1918
Catalogue details

Licence: In copyright

Credit: A manual of physics, theoretical and practical : for medical students / by Hugh C. H. Candy. Source: Wellcome Collection.

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    wish to obtain the heat equivalent metabolized in the body, or the fuel value of the food. The best results in this direction have been obtained by Atwater, and the calculations of “ energy value ” in the Keport* on the Food Supply of the United Kingdom (p. 3) are based on his values,*]' “ modified in accordance with the special characteristics of the British supply.” With this modification it is reckoned that, when consumed in human diet, the fuel value, or energy value, of 1 grm. of protein. is 4-1 Calories 1 ,, „ fat . „ 9-3 1 ,, ,, carbohydrate . . ,,4-1 ,, With these factors we can calculate the total fuel value of any given diet. About 80 per cent, of this total seems to be spent as heat, and about 20 per cent, in work. The fuel value required from a daily diet varies widely with the occupation and other personal factors of the consumer, but an average standard is probably somewhere between 3,000 and 4,000 Calories. Heat of combustion of coal, etc.—The heat liberated in the burning of a sample of coal can be estiinated as follows : The coal is finely powdered, and 2 grm. of the powder are mixed with about 24 grm. of oxygen mixture [KClOg (3 parts) + KNOg (1 part)]. The mixture is then pressed into a stout copper cylinder. In the mouth of this cylinder is inserted a dry piece of cotton wick previously soaked in a solu¬ tion of potassium nitrate, to serve as a slow match. A calorimeter, containing a sufficient quantity of Water, about 2 litres, is prepared. Wffien all is * Cd. 8421. 1917. t “The Chemical Composition of American Food Materials,” Bulletin No. 28, IT.wS. Department of Agriciilture. Revised edition, Washington, 1906.