AMOUNT OP CAEBONIC ACID EXHALED. 385 



could eat and drink, read, or sleep within it. This was connected with 

 an apparatus, by which the air was continually renewed ; and the air 

 drawn off was carefully analysed, in order to determine the quantity of 

 carbonic acid contained in it. The average per hour, in different states 

 having been ascertained, it was calculated that, allowing seven hours 

 for sleep in adults, and nine hours for children, the total' amount of 

 carbon consumed in the twenty-four was as follows : 



No. Weighing. Grains. Oz. Troy. 



1. A male, aged thirty-five, ..... 131 Ibs. 3387 or 7-0 



2. A male, aged sixteen, 115 Ibs. 3453 or 7-2 



3. A soldier, aged twenty-eight, . . . 164 Ibs. 3699 or 7-7 



4. A girl, aged nineteen, . . . . . . Ill Ibs. 2540 or 6-3 



5. A boy, aged nearly ten, 44 Ibs. 2054 or 4-3 



6. A girl, aged ten, 46 Ibs. 1930 or 4-0 



695. This estimate is perhaps rather too low, as it does not take 

 sufficient account of the great increase which is produced by exercise. 

 Another method has been adopted by Prof. Liebig, who endeavoured to 

 ascertain the total amount of carbon excreted from the body in the 

 form of carbonic acid, by comparing the amount of carbon taken in as 

 food, with that contained in the faeces and urine ; the difference being 

 set down to the account of respiration. His estimate amounts to the 

 very large sum of 13'9 oz. of solid carbon per day, which he considers 

 to be thus set free by the lungs and skin ; but this is almost certainly 

 above the truth. The observations were made upon a body of soldiers, 

 who were subjected to severe daily exertion; and they were far from 

 being exactly conducted, many of the items being set down by guess 

 only, whilst of others no account whatever was taken. We may per- 

 haps consider 10 or 11 oz. as more nearly representing the amount of 

 carbon consumed by adult men exposed to severe exertion ; whilst from 

 Prof. Scharling's experiments it may be inferred, that from 7 to 8 oz. 

 of carbon are thrown off during the twenty-four hours, by the lungs and 

 skin of adult men not using much active exertion ; to which another 

 ounce or two may be added, as the increased quantity excreted during 

 moderate exercise. In a subsequent series of experiments, Prof. Schar- 

 ling ascertained the proportion of carbonic acid given off from the 

 general surface of the human body, to be from about l-30th to l-50th 

 of the whole amount ; so that, adopting l-40th as the average, out of 

 eight ounces of carbon exhaled, only one-fifth of in ounce is set free in 

 the form of carbonic acid from the Skin. 



696. If we assume 10 oz. or 4800 grains of solid Carbon, as the 

 total amount excreted from the lungs and skin of a male adult, using 

 active exercise, in the course of twenty-four hours, we find that the 

 volume of carbonic acid thus generated must be nearly 37,000 cubic 

 inches, or more than 21 cubic feet. Of this, about 16 cubic feet are 

 probably extricated from the lungs. But it is probable, that about 10 

 cubic feet per day is nearer the ordinary average. Now it has been 

 ascertained, that the whole quantity of air which passes through the 

 chest during that time under similar circumstances, is about 266 cubic 

 feet ; so that the proportion of carbonic acid contained in the expired 

 air seems to average about 4 per cent. It is certain, however, that 



25 



