METHOD OF PROCEDURE. 13 



bustion-tube meets approximately the ground end of the calcium chloride 

 tube coming from the pump. The pump itself, installed upon a specially 

 constructed table resting on jacks, can be raised or lowered, or tilted at a 

 slight angle in any direction necessary to enable the stopper protruding 

 from the furnace to fit exactly into the drying-tube. As the whole appa- 

 ratus is now rigid glass from end to end, care is required in fitting the two 

 parts together, lest there be strain sufficient to cause serious fracture. 

 To prevent leakage during the extraction of the gas, the ground-glass 

 connection (the only source of leakage) is completely incased in a thick 

 coating of paraffine. 1 



The air in the apparatus is now pumped off until the exhaustion can 

 be carried no further, at which point the pressure may be in the neighbor- 

 hood of 0.01 millimeter. If allowed to stand for several days this vacuum 

 remains entirely without change. When ready, the burners in the furnace 

 are lighted, the separating funnel in which the gases are to be collected is 

 filled with mercury, and the evolution of the gas is under way. As fast as 

 the gases are liberated by the heat they are pumped over into the collect- 

 ing-funnel a process usually requiring about 3 or 4 hours before the last 

 traces of gas have been expelled. 



ANALYSIS OF THE GAS. 



After constant temperature has been established in the room, the gas 

 is drawn from the receiver into a Lunge nitrometer and the carbon dioxide 

 and hydrogen sulphide absorbed by the introduction of a cubic centimeter 

 of 30 per cent potassium hydroxide solution. The remaining gas is trans- 

 ferred to a gas-burette, filled with water, after which the remainder of the 

 analysis is carried on according to the method described by Hempel. 2 

 From the potassium hydroxide solution the amount of hydrogen sulphide 

 absorbed is determined by titration with N/100 iodine solution. If it be 

 desired to measure the quantity of helium and argon, the gas remaining 

 after the removal of all the constituents, except nitrogen and these inert 

 gases, is passed over metallic calcium heated to redness. 3 This absorbs the 

 nitrogen, leaving only helium and argon, which are examined spectro- 

 scopically. 



1 Whenever rocks containing a large proportion of quartz are tested, it is necessary 

 to substitute a porcelain tube, since quartz scratches glass, causing it to crack when heated. 

 The connections are readily made tight with paraffine. 



2 Hempel, Methods of gas analysis : Technical method. 



3 Travers, A study of gases, p. 102. 



