ELEMENTAEY DEMONSTEATIONS 



149 



H 



eudiometer. To facilitate the escape of the gases F is placed in warm 



water and shaken. If the 



blood froths too violently 



the frothing can be allayed 



by pouring some warm 



water on the tube E. The 



tap is so manipulated that 



the gases only, and not 



the water which condenses 



in B, aje driven over into 



the eudiometer. The water 



is returned back into F. 



Three or four exhaustions 



are sufficient to extract 



the gases. The eudiometer 



tube is filled with mercury 



and surrounded with a 



water jacket to keep the 



temperature constant. The 



eudiometer is transferred to 



a vessel of mercury and 



the volume of gas read, 



the level of mercury inside 



and outside the eudio- 

 meter being the same. The 

 temperature of the water 

 in the jacket of the eudio- 

 meter is also read and the 

 barometric pressure. Potash 



FIG. 130. Hill's blood-gas pump. 



solution 20 per cent, is then introduced into the eudiometer by means 

 of a pjpette provided with a bent end. The C0 9 is thus absorbed and 



123 



FIG. 131. The three-way tap of the mercury pump. 



the difference in volume read. Pyrogallic acid is then introduced and 

 the 2 absorbed. The remainder is N^ The temperature of the water 

 jacket is kept constant by adding cold water during the estimation. 



