1880.] in the Amount of Carbon Dioxide in the A ir, 347 



point of importance, inasmuch as the precision with which the 

 titration point can be fixed is largely dependent upon there being no 

 carbonate in suspension. 



The acid used in titration was a standard solution of sulphuric as 

 used by Dalton, 1 cub. centim. of which was equal to 1 mgrm. of 

 carbonic acid. This was substituted for the oxalic acid as recommended 

 by Pettenkofer owing to its greater stability. 



The point of neutrality was ascertained by means of a dilute alco- 

 holic solution of pure aurin ; a definitely measured quantity being em- 

 ployed, in each titration. 



The results thus obtained and set forth in the following tables, 

 fully establish the existence of a diurnal variation in the quantity of 

 carbonic acid, the night average exceeding that of the day by 0"34 

 cub. centim. in 10,000 of air; the quantities respectively being very 

 nearly in the ratio of 90 to 100. These figures are, as will be seen, 

 based upon 53 day and 62 night experiments ; there being 27 com- 

 plete day and 29 complete night observations. 



The details of the experiments contained in the accompaying tables 

 are arranged in the following order : — 



Column (1). Number of the observation. 



,, (2). Date of the observation. 



,, (3). Hour at which the observation was made. 



„ (4). Barometric reading. 



(5). 



j> Thermometric reading : dry and wet bulb. 

 State and direction of wind, when observable. 



Jars employed and results obtained from each. 

 Special remarks. 



General meteorology at the time of observation. 

 General meteorology of the preceding day or night, if 

 important. 



On looking over tbe day experiments, the averages, it will be seen, 

 are low as compared with those of the older experimenters, the final 

 average being only 2 - 96 vols, of carbonic acid in 10,000 vols, of air. 

 But it is extremely interesting to compare this result with those 

 obtained by Schulze at Rostock* during the years 1868-71. His 

 figures are, as averages : — 



* " Watts' Chem. Diet.," Suppl. Ill, 113. 

 VOL. XXX. 2 B 



