330 On the Quantity of Carbonic Acid Gas [Nov. 



to many hundreds of experiments, were generally consistent, and 

 may be comprised under the two following laws : — 



Law I. — The quantity of oxygen gas consumed, and conse- 

 quently of carbonic acid gas formed, during respiration, is not 

 uniformly the same during the 24 hours, but is always greater at 

 one and the same part of the day than at any other, that is to 

 say, its maximum occurs between 10 a. m. and 2 p. m., or 

 generally between 11 a. m. and 1 p.m.; and its minimum com- 

 mences about 8 h 30' p.m., and continues nearly uniform till 

 about S' a 30' a. m. 



Laic ii. — Whenever the quantity of oxygen gas consumed, 

 and consequently of carbonic acid gas formed, has been by any 

 cause increased or raised above the natural standard of the period, 

 it is subsequtntly as much decreased or depressed below that 

 standard, and v'ue versa. 



Illustration of Law 1. — This law is subject to some remark- 

 able variations, though I have never met with an exception to it. 

 In all my experiments there has been constantly a greater quan- 

 tity of carbonic acid gas given orf in the middle of the day than 

 at any other period of it. From what Mr. Brande advanced in 

 the paper above alluded to, I was indeed prepared to meet with 

 the reverse of this; and for some time felt inclined to suspect 

 the accuracy of my experiments, till, by varying them in almost 

 every possible manner, and with the same results, I could no 

 longer resist their united evidence. 



Generally, the degree and order of these variations are the 

 following. The quantity of carbonic acid gas, which has 

 remained stationary during the night at 3"30 per cent.,* its 

 minimum, about 3 h 30' a. m.,f suddenly begins to increase, at 

 first slowly, and afterwards more rapidly, till about noon, when 

 it is usually as high as 4*10 per cent., or its maximum; from 

 this point, however, it almost immediately begins to sink, at first 

 rather quickly, and then more slowly, till about 8" 30' p. m.,f 

 by which time it generally arrives again at its minimum, 3'30 

 per cent., when it remains stationary, as before observed, till 

 the morning. Hence the quantity given off in the middle of the 

 day, when it is at its maximum, exceeds that given oft' in the 

 night, when it is at its minimum, by about 4- of the whole. 

 The mean quantity given oft' in the 24 hours is 3"45 per cent. 

 (See Table 1.) 



* By this is meant that fur every 100 cubic inches of air inspired, 3\30 cubic 

 inches of oxygen gas arc consumed, and consequently of carbonic acid gas 

 formed. The -■arm- is to be Understood of all the subsequent numbers. 



+ That is, at the beginning and end of twilight. Many circumstances have 

 occurred to induce me to believe that the presence and absence of the sun along 

 regnla e these variations. Future observations'] however, mu^ decide this, 

 curious question. 



