45 



223 



\ 



r)' 



m. 



J 



M 



N 



air is drawn out through the porous phigs M and N hy means of the mercury pump. 

 The exhausted tube B is now used as a barometer tube, while the vohime of tiie 

 gas under examination is gauged in tube A. 



To introduce the gas into the measuring tube 

 A, the uppermost part of the latter is narrowed, the 

 outward diameter being only 6 mm., so that the 

 collecting tube G may be pushed over it. By sinking 

 the collecting tube G, the gas contained in it is 

 sucked through the porous plug into A, provided 

 that the pressure in A is less than that of the 

 atmosphere. The apparatus has turned out to be 

 exceedingly convenient for rapid and accurate mea- 

 surements of small volumes of gas, which are col- 

 lected by means of the mercury pump in the collect- 

 ing tubes. This method ensures that the gas is quite 

 safely transported into the measuring tube. Besides 

 this, the measurements of the volume can be per- 

 formed at a suitably low pressure, so that considerable 

 accuracy can be obtained in spite of the volumes to 

 be measured being extremely small. 



In order to prevent impurities of air being carried 

 by the mercury through the indiarubber tube into 

 the tubes A and B, the glass lube connecting the 

 indiarubber tube with the measuring tubes is pro- 

 vided with an air receiver F. This receiver is shown 

 in section in Fig. 12. The air carried by the mer- 

 cury through the inlet b, is collected in the space 

 beneath the porous plug A". There is usually great 

 pressure in this space, and the gas collected is there- 

 fore forced up through the plug, and escapes into the 

 atmosphere. On the other hand, the mercury resting 

 above the plug prevents the air from penetrating 

 into the plug. When the apparatus is arranged in 

 this way, the small amount of gas under ordinary 

 pressure contained in the porous plug is seldom 

 rarified, and never to such an extent that it cannot 

 be contained in the bulb of the receiver, without any danger of the air escaping 

 into the measuring tubes. 



Before abandoning this section on the apparatus and methods employed in 

 this investigation, I shall briefly describe the mercury air pump I used. It is an 

 air pump with falling mercury. The construction of the glass tube through which 



kn 



V=Ja 



Fig. 12. 



