[29] See Horace Fletcher, The A-B-Z of our own Nutrition. (1903.) New York. p. 48.
[30] For a fuller account of this study, see Chittenden, Physiological Economy in Nutrition. Popular Science Monthly, June, 1903.
[31] All figures for nitrogen throughout the book, whether referring to food, urine, or fæces, were obtained by exact chemical analysis, using the Kjeldahl-Gunning method.
Uric acid was determined by the method of Folin, i. e., precipitation of the urine with ammonium sulphate, etc., and titration with potassium permanganate.
Phosphoric acid was estimated by titration with a standard uranium solution, using potassium ferrocyanide as an indicator.
At times, as will be seen from the tables, nitrogen, uric acid, etc., were not determined in each day’s urine. In such cases, an aliquot part of each twenty-four hours’ urine was taken and the analyses made with the mixed samples for the given period, the figures thus obtained showing the average daily composition for that period.
[32] All foodstuffs were analyzed from large samples, to diminish as much as possible the errors of analysis. Nitrogen was determined by the Kjeldahl-Gunning method, the figures given being the average of closely agreeing duplicate analyses.
While nitrogen was thus determined in every sample of food by direct chemical analysis, the fuel value of the food was calculated mainly by use of the data furnished by the Bulletin issued from the U. S. Department of Agriculture, Office of Experiment Stations. No. 28
[33] The fæces of this period were separated by lampblack. They were dried on a water-bath after admixture with alcohol and a little sulphuric acid, nitrogen being determined by the Kjeldahl-Gunning method on samples of the dry mixture from the six-day period.
[34] The figures given for weight of fæces during this balance period are tabulated for convenience as above, but naturally the last yield was not obtained until the 8th of March. The total of 182 grams, however, is the exact amount of air-dry fæces collected between the two charcoal layers, marking off accurately the balance period.