68 Mr Dal ton on the Qumitity of Food 



upon 48^ of urine per day. Berzelius has not neglected the 

 analysis of the faeces ; of 100 parts, three-fourths may be esti- 

 mated as water, and the rest do not seem to contain more than 

 10 parts of carbon. This would give half an ounce of carbon 

 in 5 ounces. Hence we may infer that one ounce, a little more 

 or less, of carbon, is carried off from the body daily through 

 these two channels. The remainder, 10^ ounces, must there- 

 fore be spent in the insensible perspiration. 



The quantity of insensible perspiration from the skin, cannot 

 be easily determined by direct experiment. That from the 

 lungs may be approximated from known facts. I have shewn 

 (See Manchester Memoirs, vol. ii. new series, page 27,) that I 

 produced by breathing, in the space of twenty-four hours, 2.8 lbs. 

 troy of carbonic acid gas. This is equivalent to .78 parts of 

 1 Ih. troy of carbon = .642 parts of 1 lb. avoirdupois = 10^ 

 ounces nearly. Now, when I estimated the quantities of car- 

 bon in the several articles of food, &c. just related, I had no 

 recollection of this quantity of carbon expended in breathing ; 

 it may be well supposed, then, that I was highly gratified to find 

 by the calculation, that the difference of the two quantities, found 

 by such different modes of investigation, was only a quarter of 

 an ounce. 



With respect to the aqueous vapour exhaled from the lungs, 

 I have determined, in the essay quoted above, (page 29) that the 

 highest estimate of the quantity I exhale, cannot exceed 1.55 lbs. 

 troy = 1.275 lbs. avoirdupois, =: 20J ounces avoirdupois; if 

 to this we add 10;^^ ounces of carbon, we have 30j ounces for 

 the carbon and water expended from the lungs in one day, 

 and this taken from 37^ leaves 6| ounces per day, for the in- 

 sensible perspiration from the skin, which, if the above estimate 

 be allowed, must consist of 6J ounces water, and one quarter of 

 an ounce carbon. According to this, the matter perspired from 

 the lungs is five times as much as that from the whole surface 

 of the body. 



If, instead of carbon, we trace the element azote into and 

 out of the body, we shall find from our data, that from butchers' 

 meat, cheese, and milk, about 1^ ounce of azote is taken into 

 the stomach daily, and nearly as much passed off by urine and 

 faeces. 



