28 COMPARISONS OF RESPIRATORY EXCHANGE. 



The advantages of the glass bottle over the silver-plated can are the 

 decreased expense of construction, the rapidity with which the bottle 

 can be filled and closed, the readiness with which it may be made air- 

 tight, and the fact that, as the carbon dioxide is absorbed, the change 

 in color of the soda-lime to a chalky white is easily seen. When this 

 discoloration extends to the bottom, it is evident that the bottle 

 should be refilled. Experimenting has shown that when air enters 

 the bottle at the top and is withdrawn from the bottom through the 

 tube, the results are more satisfactory than when the passage of air 

 is reversed. 



The method of making the soda-lime has been fully described in a 

 previous publication. 1 In order that the soda-lime may be efficient, it 

 is always prepared in such a way that the finished product is slightly 

 moist. Much of the difficulty found in the use of soda-lime as an 

 absorbent for carbon dioxide has been due to the fact it was too dry. 



Water-absorber. — In the passage of absolutely dry air through moist 

 soda-lime, moisture is taken up by the air. As the carbon dioxide is 

 determined by weight, it is necessary to know the amount of moisture 

 leaving the carbon-dioxide absorber. In the first two or three years of 

 experimenting with this apparatus, a form of absorbing vessel was used 

 which was adapted from the bottom part of a 500 c.c. Kipp generator. 

 The lower bulb was filled about half full of strong sulphuric acid. The 

 upper bulb was filled with broken pumice stone and drenched with 

 sulphuric acid. A bent glass tube led from the top of the bottle, 

 through a rubber stopper, into the acid to a depth of 5 to 10 mm. The 

 side outlet in the upper bulb was used as the exit of the absorber. This 

 form was employed for several years and proved satisfactory, but was 

 subsequently replaced by the absorber devised by Dr. H. B. Williams, 

 of the Department of Physiology at Columbia University, New York. 

 The Williams absorber, which is shown in detail in figure 6, is 9.5 cm. 

 in diameter and 15 cm. high. It is so constructed that the air entering 

 the apparatus is broken up into a number of bubbles during its passage 

 into the acid by means of two concentric rows of openings. When 

 charged with 450 c.c. of sulphuric acid, it can be relied upon to absorb 

 completely at least 10 gm. of water-vapor from an air-current of 35 liters 

 per minute without allowing any weighable amount to pass. The 

 bottle is closed with a rubber stopper and fitted with hose-couplings at 

 the ends; the outside is protected with a wire basket which has a handle 

 for carrying. The Williams bottle and soda-lime container can be 

 weighed together on a Sauter balance, their combined weight being 

 about 5,000 gm. 



Apparatus for testing completeness of carbon-dioxide absorption. — 

 A 100 c.c. Erlenmeyer flask with a two-hole rubber stopper is partly 



*Atwater and Benedict, Carnegie Inst. Wash. Pub. 42, 1905, p. 29; also Benedict, Deutsch. 

 Archiv f. klin. Med., 1912, 107, p. 166. 



