44 GAS ANALYSIS. [CH. II 



readings of the gas-volume. To obtain the result it is 

 necessary to reduce the readings of the calibrated tube 

 (before and after the injection of KHO) to C. and to 

 1 meter mercury pressure, and to make allowance for 

 water vapour tension, etc. This is to be done according 

 to the formula of Btmsen 1 . 



It is by no means necessary to employ a tube of the 

 above-described form. We employ tubes of test-tube 

 form of 2 cm. internal diameter and containing 100 c.c. 

 Oleander leaves (which are especially good material in 

 the winter months) fit these tubes well. The mercury is 

 raised to the desired height by a thick-walled india- 

 rubber tube pushed up into the cavity, and connected 

 with a water air-pump. The rubber tube is then closed 

 between the fingers and drawn out : if in this process a 

 few drops of mercury are drawn into the tube, they may 

 be sucked (by turning on the pump) into a bottle fitted 

 like a washing bottle, w r hich serves as a trap between the 

 pump and any vessel to which suction is to be applied. 



(51) Winkler-Hempel apparatus. 



For demonstration purposes, where it is desirable to 

 avoid barometer readings, calculations, &c., fair results 



(y - m) (6 - 6t - 6 2 ) 



1 + 0-00366 



Where v l = the reduced volume of gas. 



v =the observed volume. 



m = the correction for meniscus. 



b = the barometric reading. 



t 1 = the mercury pressure in the eudiometer. 



& 2 = the water-vapour tension at the temperature t. 

 See Bunsen and Itoscoe, Gasometric Analysis. 



