VOLUMETRIC METHOD 329 



tube by a rubber joint, thus aiding in inserting it into the V- 

 shaped nozzle of the azotometer. 



The azotometer used is the one devised by Schiff and modified 

 by Johnson and Jenkins. 83 



The V nozzles may be got separately and joined to any 

 good burette by a rubber tube. The water-jacket is not neces- 

 sary, but the apparatus can be left exposed until it reaches room 

 temperature. 



Any form of mercury pump capable of securing a vacuum 

 may be used, but the one just described is commended by sim- 

 plicity, economy, effectiveness, and long use. 



288. The Pump and Combustion Furnace. The pump and 

 combustion furnace, as used in the above process, are shown in 

 Fig. 14. The pump is constructed as just described, and rests in 

 a wooden tray which catches and holds any mercury which may 

 be spilled. The furnace is placed under a hood which carries 

 off the products of the burning gas and the hot air. A well 

 ventilated hood is an important accessory to this process, espe- 

 cially when it is carried on in summer. A small mercury pneu- 

 matic trough catches the overflow from the pump and also serves 

 to immerse the end of the delivery tube during the exhaustion 

 of the combustion tube. 



The other details of the arrangement and connections have 

 been sufficiently shown in the previous paragraph. 



289. Volumetric Method of Bureau of Chemistry. It has been 

 found convenient to vary slightly the method of the official 

 chemists in the following respects: The tube used for the com- 

 bustion is made of hard refractory glass, which will keep its shape 

 at a high red heat. It is drawn out and sealed at one end after 

 being well cleaned and dried. It should be about 80 centime- 

 ters in length and from 12 to 14 millimeters in internal diameter. 

 The relative lengths of the spaces occupied by the several con- 

 tents of the tube are approximately as follows : Sodium bicar- 

 bonate, two ; asbestos, three ; coarse copper oxid, eight ; fine copper 

 oxid, containing sample, 16 ; coarse copper oxid, 25 ; spiral copper 



M American Chemical Journal, 1880-81, 2 : 27. 



