376 IT. Gr. Mixter — Deportment of Charcoal with 



tact with the wire. In many of the trials 

 the charcoal ceased to glow as soon as the 

 current of electricity was stopped, burning 

 readily, however, when ignited in moist 

 oxygen. The failures in the experiments 

 led to an investigation of the burning of 

 charcoal. Baker* in his experiment used 

 charcoal previously ignited in chlorine. 

 Snch charcoal contains chlorine unless 

 heated for a long time to a white heat,f 

 and the writer has frequently observed that 

 chlorinated charcoal only partly burns at 

 the temperature of a combustion furnace 

 in oxygen dried as for organic analyses, 

 and that after the coal has ceased to glow 

 it ignites again on admitting moist oxygen 

 and bums completely, Dubrunfaut^: failed 

 to burn sugar charcoal mixed with copper 

 oxide in a current of dry oxygen. Other 

 chemists have alluded to the difficulty 

 attending combustions in dry oxygen ; 

 Dumas,§ however burned graphite in oxygen dried by solid 

 caustic potash and sulphuric acid. 



A Hoffmann apparatus, snch as shown in fig. 1, was used in 

 the investigation. It held about 350 cc of gas and had heavy 

 platinum wires passing through the stopper to the small wire 

 which held the charcoal. To prepare it for use sufficient mer- 

 cury was poured in to fill the tube at the bend below the stop- 

 cock and a short wide tnbe containing phosphorous pentoxide 

 was placed in the neck below the bulb which was then closed. 

 Xext the charcoal and all the platinum below the stopper were 

 heated in a blast lamp. The charcoal used in 1, £, 3 and 4-, 

 was allowed to cool in carbon dioxide, but the sugar charcoal 

 of the other experiments was put into the apparatus while 

 glowing as it did not burn in air. The apparatus was then 

 filled with oxygen by passing through it about two liters of the 

 gas dried as for organic analyses. In 1, 2, 3 and .£, the sup- 

 porting wire passed through a hole in the charcoal, thus giving 

 only one point of contact, in the other experiments it was 

 placed in an inverted cone of platinum wire. 



Experiment 1. — 0*033 gram of dense wood charcoal pre- 

 viously heated to redness tor an hour was taken, and the gas 

 was allowed to dry a day. The charcoal ignited when heated 

 by a current of electricity through the wire and burned com- 

 pletely without further heating. The volume of the gas at 



* Loc. cit. 



% Comp. rend., Lxxiii, 1395. 



f This Journal, p. 364. 

 fc$ Comp. rend., lxxiv, 131. 



