Experiments on the metabolism of matter and energy in the human body / By W.O. Atwater, PH.D., and F.G. Benedict, PH.D., with the cooperation of A.W. Smith, M.S., and A.P. Bryant, M.S.

  • Atwater, W. O. (Wilbur Olin), 1844-1907.
Date:
1899
Catalogue details

Licence: Public Domain Mark

Credit: Experiments on the metabolism of matter and energy in the human body / By W.O. Atwater, PH.D., and F.G. Benedict, PH.D., with the cooperation of A.W. Smith, M.S., and A.P. Bryant, M.S. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

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    While this is thecommon usage in metabolism experiments, it isof course inc'OiTet't iu so far as the urine contains creatinin and allied compounds which were in the food. The error thus introduced, however, is not large. The carbon and hydrogen in organic combination iu the urine represent partially oxidized compounds, and the heat of combustion of the dried residue of the urine is a measure of the amount of energy which is carried away from the body in these partially oxidized compounds. Sdinplinf/ (Old totah/.sis.—The urine of six-hour periods, beginning with the experimental day at 7 a. m., was collected in glass jars, tightly sealed, and, after remaining in the chamber for about three hours in order to come to the temperature of the apparatus, was jjassed out through the food aperture. It was then weighed and its specific gravity taken, after which an aliquot portion, usually one-half, was reserved to make a part of a composite sample for the day, and the remainder was used for the determination of nitrogen and other constituents. The nitrogen was determined in the fresh urine by the Kjeldahl method. Portions of 100 or 200 grams of the composite sample for the whole experiment were evaporated to dryness in a partial vacuum, and deter- minations of carbon and hydrogen were made in this dried residue. Loss of urea in dry in f/.—Even when urine is dried in a vacuum at com- paratively low temperature there is danger of some decomposition by which nitrogen may be lost, in the form either of ammonia or, more prob ably, of ammonium carbonate. The process of drying is also tedious. For this reason in the latter experiments an attempt was made to dry the urine at 100° C. and to determine the loss of nitrogen during this drying. In order to estimate the amount of this loss of nitrogen several samjdes were dried in a flask over a water bath or calcium chlorid bath giving a temperature of from 100 to 105*^ C. A current of air was forced through the flask by means of a water blast. This air was freed from carbon dioxid by passing it over soda-lime before it reached tiie flask. The air as it came from the flask was passed through a known amount of a standard solntion of acid in another flask, after which it was dried by ]>assing through suli)huri(! acid and the carbon dioxid removed by soda lime. After the urine had been brought nearly to dryness in the first flask, the standard acid in the second llask was titrated and the amount of nitrogen in the ammonia wliich had been absorbed by the acid was cahuilated. The increase in weight of the soda lime tube and the sulplinricacid tube immediately following it gave the amount of carbon dioxid that liad been given off from the urine. In two exi)eriment8 the projwrtions of nitrogen and of carbon dioxid giv(;n off conesi»ondc(l (piite nearly to the i)ro])ortions in ammo- nium carbonate, 'i'lie natnial inference was that it would be within the limits of error to assume that all the nitrogen and carbon lost in drying were in ammoninni <;arbonate. Of conrse this conld not be exactly true, becaus«^ there is a certain amount of free carbon dioxid iu the urine.