1856.] and the Means of Determining its Amount. 243 



given number of people have remained in it. Then the quantity of 

 carbonic acid which this number of people would produce in the 

 given time must be calculated, and by deducting the quantity found, 

 from the total quantity produced, the quantity of air which escaped 

 from the given space in that time can be determined. 



The following examples from M. Leblanc's paper will best 

 illustrate this method. 



M. Leblanc remained himself for ten hours in a perfectly closed 

 atmosphere, the capacity of the chamber = 459 cubic feet (13 met. 

 cube) ; this gave him less than one cubic foot of air per minute 

 ( = • 76 cubic foot). At the end of this time he found the car- 

 bonic acid = 0.0075 in volume, or one part carbonic acid in one 

 hundred and thirty-three parts of air. 



He found in a soldier's sleeping-room 25 men in a cubic space, 

 which if perfectly closed would have given about 0*8 cubic foot per 

 minute per man. Analysis gave 3 parts carbonic acid in 1000 air. 

 Had the room been perfectly closed whilst they slept, there should 

 have been 9 parts carbonic acid. Hence, 2' 4 cubic feet of air per 

 minute had been given. 



In another sleeping room, with 52 soldiers, the capacity of the 

 room would have given 0*6 cubic foot per minute, per man, 

 3 parts carbonic acid per 1000 were found ; if perfectly closed, there 

 would have been 10 parts. Hence, about 2 cubic feet per minute 

 had been given to each man. 



In a much smaller and worse ventilated room, with 1 1 soldiers 

 and of capacity about 0*5 cubic foot per minute ^per man, nearly 

 9 parts of carbonic acid were found in 1000 air. If closed, there 

 would have been 14 parts. Hence only 0*8 cubic foot of air per 

 minute was given to each man. 



The method followed by M. Leblanc for determining the car- 

 bonic acid was the following : — an aspirator which held about 

 43 pints of water had tubes fitted to it, for absorbing water and 

 carbonic acid. In the course of one hour about 1 456 cubic inches, 

 or • 844 cubic foot of air was drawn through the tubes by the escape 

 of the water ; on weighing the tube which absorbed the carbonic 

 acid in the second experiment mentioned above,*there was a gain of 

 2*62 grs. corresponding to 5' 2 cubic inches of carbonic acid. 



In his previous experiments on confined air, M. Leblanc used 

 two large globes, holding each about 32 pints, which were ex- 

 hausted and then filled with the air to be examined ; this was drawn 

 through the absorbing tubes by two other exhausted globes. 



For my experiments on the close air in St. Pancras workhouse, 

 I obtained a long tube, which, through the kindness of Mr. 

 De la Rue, was accurately graduated ; this I filled myself with air in 

 the rooms ; the tube was then closed and brought to the laboratory 

 of the College of Chemistry, placed over mercury, and potass bulbs 

 were introduced by Mr. Witt, and the height of the mercury noted. 

 After 12 hours, the height was again noted, and by corrections for 



