250 CHEMISTRY OF RESPIRATION. 



that a characteristic sound is emitted. Not unfrequently it is due to irritation of 

 the gastric mucous membrane, and sometimes it is a very troublesome symptom in 

 uraemic poisoning.] 



Chemistry of Respiration. 



121. Quantitative Estimation of Carbonic Acid, 

 Oxygen, and Watery Vapour, 



1. Estimation Of C02- 1. The volume of C0 2 is estimated by means of the 

 anthracometer (Fig. 110, II) of Vierordt. The volume of gas is collected in a gradu- 

 ated tube, r r, provided with a bulb at one end (previously filled with water and 

 carefully calibrated, i.e. t the exact amount which each part of the tube contains is 

 accurately measured), and the tube is closed. The lower end has a stop-cock, h, 

 and to this is screwed a flask, w, completely filled with a solution of caustic potash; 

 the stop-cock is then opened, the potash solution is allowed to ascend into the 

 tube, which is moved about until all the C0 2 unites with the potash to form 

 potassium carbonate. Hold the tube vertically and allow the potash to run 

 back into the flask, close the stop-cock, and remove the bottle with the potash. Place 

 the stop-cock under water, open it and allow the water to ascend in the tube, when 

 the space in the tube occupied by the fluid indicates the volume of C0 2 which 

 is combined with the potash. 



2. By weight. A large quantity of the mixture of gases which has to be investi- 

 gated is made to pass through a Liebig's bulb filled with caustic potash. The 

 potash apparatus having been carefully weighed beforehand, the increase of weight 

 indicates the amount of C0 2 which has been taken up by the potash from the air 

 passed through it. 



3. By Titration, A large volume of the air to be investigated is conducted 

 through a known volume of a solution of barium hydrate. The C0 2 unites with 

 the barium and forms barium carbonate. The fluid is neutralised with a standard 

 solution of oxalic acid, and the more barium that has united with the C0 2 the 

 smaller will be the amount of oxalic acid used, and vice versa. 



II. Estimation Of Oxygen. According to volume (a) By the union of the 

 O with potassium pyrogallate. The same procedure is adopted as for the estima- 

 tion of C0 2 , only the flask, n, is filled with the pyrogallate solution instead of 

 potash. (6) By exposure in an eudiometer (see Blood gases, p. 55). 



III. Estimation Of Watery Vapour. The air to be investigated is passed 

 through a bulb containing concentrated sulphuric acid or through a tube filled with 

 pieces of calcium chloride. The amount of water is directly indicated by the 

 increase of weight. 



122. Methods of Investigation. 



I. Collecting the Expired Air. 1. The air expired may be collected in the cylinder 

 of the spirometer ( 108) which is suspended in concentrated salt solution to 

 avoid the absorption of C0 2 . 



