APPENDIX. 



237 



S with sources of carbon dioxid and oxygen, respectively. All of these gas-streams 

 pass through small wash-bottles or bulbs to render the speed of the stream ascertain- 

 ablr, and are controlled by screw-clamps on short pieces of rubber tubing. Do not 

 heat the part of the tube near the cork, and keep it free from any support in order 

 to avoid the danger of charring the cork. 



(2) COMBUSTION. 



Place from 1 to 5 grams in weighed platinum boats. Everything being arranged 

 as described in section (1), close the clamps at S and D, controlling the oxygen. Pass 

 a slow current of carbon dioxid in through K, and heat the part of the tube from E to 

 H to a low red heat. It is advisable to have the temperature a little higher at E than 

 at H, and diminish it gradually along the tube from E toward H, maintaining at the 

 latter point a temperature below dull red heat. When the part EH is hot, admit a 

 very slow stream of oxygen through D, the carbon dioxid stream being left unaltered. 

 Next heat very gradually from E toward the boat M. Light one burner near A to 

 prevent any back distillation. The instant the substance in the front part of the 

 boat M begins to char, increase the oxygen stream through D, and after a short time 

 usually only a few seconds the platinum spiral at E begins to glow, and the gases 

 from M catch fire in the excess of oxygen and burn with a small flame at or near4he_ 

 spiral. After M is charred light burners under M'. At the beginning have a fairly 

 strong oxygen stream going through 

 D. When the gases have caught 

 fire, the adjustment of the stream 

 at D is an easy matter, the position 

 and shape of the disk of the flame 

 itself indicating the state of affairs. 

 In fig. 2 the line ab shows in section 

 the position assumed by the disk of 

 flame when the oxygen supply is 

 properly adjusted. When the flame 

 becomes vertical and travels off 

 toward the substance, assuming the 

 position ef, for example, a needless 

 excess of oxygen is being used. On 

 the other hand, if the oxygen be FIG. 2.-Detail of combustion tube, 



insufficient, the gases from the char tilt the disk of flame into some such position as 

 that represented by cd. In this case the lower edge d begins to flutter, the flame 

 turns smoky, and carbon is deposited on the first portions of the sodium carbonate. 

 The soot, however, almost instantly disappears if the oxygen supply is momentarily 

 increased. A supply of oxygen which just prevents the deposition of soot is sufficient. 



From this moment on, the combustion goes forward almost automatically. Grad- 

 ually extend the heat toward the front end of the tube the cork end avoiding 

 a high temperature. All that is necessary in this stage is the complete charring of 

 the substance, and this takes place below red heat. The gases from the charring 

 mass are carried by the stream of carbon dioxid (which may now be made very slow) 

 to the flame. It will be seen at once that it is impossible for an explosive mixture to 

 be formed between D and A, since the gases are prevented by the carbon dioxid 

 stream from mixing with oxygen until they reach the surface of the flame, beyond 

 which sharply defined surface there is a large excess of oxygen. 



When the whole substance is charred, the flame assumes a vertical position and 

 travels slowly toward the boat. If an attempt is now made to bring it back to ab by 

 diminishing the supply of oxygen, the flame grows smaller, flickers, and goes out. At 

 this point turn up the burners along the section from D to A, shut off the carbon dioxid, 



