2 



Dr. F. S. B. Francois de Chaumont on [May 4, 



for health, taking the carbonic acid as the measure. The results showed 

 that the mean amount of carbonic acid as respiratory impurity in air un- 

 distinguishable by the sense of smell from fresh external air was under 

 0-2000 per 1000 volumes *. My object in the present note is to call 

 attention to the relative effects of temperature and humidity upon the 

 condition of aii', as calculated from the same observations. 



If we adopt the figures of Class Xo. 1 (that is " fresh," or not differ- 

 ing sensibly from the external air) we find the following : — 

 Temperature. Huraidity. Carbonic acid. 



63° F. 73 per cent. 0-1943 per 1000 volumes. 



If, now, we arrange the observations according as they differ from the 

 above standard of temperature and humidity, and note the record of 

 sensation attached to each, we may ascertain how far the said record 

 departs (if at all) from what it ought to have been as calculated from the 

 actual CO2. To do this we may employ the numerical values of the 

 different classes, taking ISo. 1 (fresh) as unity, thus : — 



Class. Sensation. Value. 



Xo. 1. Fresh 1-00 



2. Eather close 2-13 



3. Close 3-46 



4. Extremely close .... 4'66 



Taking each observation and dividing the CO^ found by the mean quan- 

 tity of No. 1, viz. 0-1943, we get a number which wiU give the theore- 

 tical value of its effect upon the se nes ; and by comparing this with 

 the actual value of the recorded sensation, we can note whether the 

 difference is plus or minus, if any. All observed quantities of CO^ below 

 0-1943 are considered equal to that number, and all quantities above 

 0-9054 as equal to it, as the sense of smell does not seem capable of 

 differentiating quantities except between those limits. 



Out of 458 fully recorded cases, 186 gave a recorded sensation in excess 

 of the theoretical value — that is, the air seemed less pure than would 

 have been expected from its CO2. In these the average temperature and 

 humidity were both above Class 1. 



* In the former paper the amount was given at O'lSSO per 1000; but on revising the 

 calculations, a previously imobserved error was found in one of the constants employed, 

 the cori'ection for which would have the effect of altering the figures a little, the 

 changes being as follows . — 



Eespiratorj- impurity as CO.,. 

 Classes. Original figures. Corrected figures. 

 No. 1. Fresh 0-1830 0-1943 



2. Eather close 0-3894 0-4132 



3. Close 06322 0-6708 



4. Extremely close 0-8533 0-9054 



Except for the sake of rigid accuracy the difference is immaterial, as I adopted 0-2000 

 as the hmit of respiratory impurity in an air-space well ventilated, and the corrected 

 number 0-1943 is still below that. 



