216 ANNUAL OF SCIENTIFIC DISCOVERY. 



different proportions, through the skin and the lungs. It was, there- 

 fore, necessary to determine directly one of the two quantities, and 

 Professor Pettenkofer conceived that this could only be done by con- 

 ducting a current of air, of known and invariable strength, over a 

 man, and then determining the addition of carbonic acid and water 

 to this current of air. 



As pattern for such an apparatus, the learned professor took the 

 ordinary stove of an apartment. AS long as there is a thorough 

 draught in the chimney, no smoke escapes through the joinings and 

 the door of the stove ; but the air passes from without everywhere 

 on the stove, in order to ascend the chimney. If an accurate meas- 

 urement of the quantity of air moving in the flue which conducts the 

 smoke* from the stove to the chimney can be made ; and if the com- 

 position of the air which enters and leaves the stove can be ascer- 

 tained by examining a fraction of it, all conditions are fulfilled which 

 are necessary for showing that which, during combustion in the 

 stove, is mixed with the current of air. Prof. Pettenkofer now 

 thought that it would be the best plan to construct, within a large 

 apartment, a small room of sheet iron in place of the stove. This 

 small room should be of five feet square, and furnished with an iron 

 door, with a sky-light and windows. The latter should be cemented 

 as air-tight as possible, and the walls and the ceiling should be sol- 

 dered as air-tight as possible. The door should be furnished with 

 movable openings, for rendering possible the entrance of air through 

 other points than on the hinges, according as might be reqm'recl. On 

 the side opposite to the door two openings, one below and the other 

 above, should pass by two flues outside of the small room, into a sin- 

 gle large flue, in which the air streams toward that part of the ap- 

 paratus which serves as a chimney. Tin's part, which should be 

 placed in another room of the house than that in which the iron 

 room is, should consist of two sucking cylinders with ventilating 

 valves, which should be equally moved, at an ad libitum height, by 

 means of a strong clock-work. The falling weignt of the clock-work 

 should, in proportion as it sinks, be continually wound up again by 

 means of a small steam-engine, so that an ad libitum and invariable 

 quantity of air should be kept streaming through the door of the 

 iron room towards the sucking cylinders. The air would then not 

 be able to arrive in these cylinders before having passed through a 

 continually working apparatus for measuring its quantity. A large 

 gas-meter, of such dimensions that three thousand cubic feet English 

 might be accurately measured with it within the hour, seemed for 

 this purpose to be necessary to Prof. Pettenkofer. In order to ex- 

 amine a fraction of the air which would enter the openings of the 

 door and other crevices that might perhaps exist, and which would 

 stream out through the common flue from the apparatus towards the 

 gas-meter; and in order to calculate from the obtained differences 

 of the water and the carbonic acid that quantity winch had been 

 added to them within the apparatus, two aspirators appeared to be 

 necessary, each one of which would suck simultaneously an equal 

 proportion of air. The water mixed with the air should then be ab- 

 sorbed by sulphuric acid, and weighed ; the carbonic acid should be 

 measured by sucking the air in fine vesicles through a certain quau- 



