METHODS OF INVESTIGATION. 



22 7 



until all the carbon dioxid is absorbed by the potassium, with the forma- 

 tion of potassium carbonate. Then the solution is allowed to run back into the 

 bottle, the stop-cock is closed, and the potassium-bottle is removed. The end of 

 the tube is dipped into water, and the latter is allowed to rise in the tube. The 

 volume of water thus admitted is equal to the volume of carbon dioxid removed 

 by the potassium-solution. 



Determination by Weight. A considerable volume of the gaseous mixture 

 is passed through Liebig's bulbs, filled with a solution of potassium hydrate and 

 arranged in a combination such as that of Scharling's apparatus (Fig. 86, e, f, g). 



Determination by Titration. A considerable volume of the air to be exam- 

 ined is conducted through a definite quantity of a known solution of barium 

 hydrate. The carbon dioxid combines to form barium carbonate. The solution 

 is then neutralized with a titrated solution of oxalic acid. The quantity of oxalic 

 acid necessary to neutralize the remaining barium hydrate varies inversely with 

 the amount of barium already combined with the carbon dioxid. 



Estimation of the Oxygen. 



The volume of oxygen may be determined in two ways: (a) By combining the 

 gas with potassium pyrogallate. Vierordt's anthracometer may be employed for 

 this purpose, substituting a solution of potassium pyrogallate for that of potassium 

 hydrate. (6) By explosion in an eudiometer. 



Estimation of the Aqueous Vapor. 



The volume of air to be examined is allowed to pass either through a bulb- 

 apparatus containing concentrated sulphuric acid, or through a tube filled with 

 pieces of calcium chlorid. In both cases the water is energetically abstracted, 

 and the increase in weight will give the amount of water in the air examined. 



METHODS OF INVESTIGATION. 



Collecting the Expired Air. 



If only the gases exhaled from the lungs are to be collected, the bell-jar 

 of the spirometer (Fig. 76) may be used, suspended in a concentrated solution 

 of sodium chlorid to limit the gas-absorption. Andral and Gavarret permitted 

 several successive expirations to be made into a large bell- jar (Fig. 85, I, C). 

 For this purpose a mouth-piece M was applied in an air-tight manner over the 

 mouth, the nostrils being closed; the direction of the air-current was regulated by 



FIG. 86. Respiration Apparatus of Scharling. 



means of two so-called Muller's mercurial valves (a, b), which allowed the air to 

 pass only in the direction of the arrows. 



If the gases given off from the skin during perspiration are to be investigated, 

 as well as those from the lungs, then the subject must be placed in a closed cham- 

 ber, from which the gases may be withdrawn for experimental purposes. 



The Most Important of the Respiration Apparatus. (a) The apparatus of Schar- 

 ling (Fig 86) consists primarily of a closed chamber A, capable ot contain: 

 a human being. The chamber has an afferent opening z, and an efferent opening 

 b. The latter is connected with an aspirating contrivance C, consisting of a g< 

 sized barrel filled with water. It is evident that when the water flows out ot the 



