ORGANIC ANALYSIS. 



703 



FIG. 92. of tne furnace, to prevent the cork being burned and 

 B the chloride of calcium tube being heated, by radiation 

 from the furnace. But the fore end of the tube, which 

 is empty and projects an inch beyond the furnace, 

 should be kept so hot during the whole operation that no 

 water condenses in it; in the course of twenty minutes or 

 half an hour the screen has been moved to the end of the tube, 

 and the combustion completed. When the evolution of gas 

 stops all at once, the combustion is certainly complete, and a 

 good result is obtained ; the tube should be heated red hot, but 

 not to bright redness ; it begins to stick to the supports when 

 heated too hot. 



As soon as the evolution of gas terminates, the potash ley 

 begins to rise into the bulb m. The pointed extremity of the 

 combustion tube should then be broken by means of a pair of 

 pliers, after removing the charcoal from that end of the furnace. 

 An open tube h, 12 or 15 inches long, is then placed over the 

 opened end, and supported by a stand, (Fig. 93), while by 



FIG. 93. 



means of the suction tube B, a certain quantity of air is drawn 

 by the mouth through the potash apparatus. The whole wa- 

 tery vapour and carbonic acid remaining in the combustion 

 tube, are thus brought into the chloride of calcium tube and 

 potash apparatus, and completely absorbed. 



The data furnished by the combustion afford the means of 

 calculating the composition of the substance analysed, as the 

 composition of water and carbonic acid is known, the former 



