254 PROCEEDINQS OF THE AMERICAN ACADEMY 



the tube is being heated, and the other end raised and extending to- 

 wards the substance, has been found to answer a good purpose. 



2. In the case of volatile bodies (I have not yet analyzed any others 

 by this process), I have found the combustion to proceed most satisfac- 

 torily when, having first heated about four or five inches of the anterior 

 portion of the tube, which includes the oxide of copper, and started the 

 flow of oxygen, I apply the heated bar to the bulb containing the sub- 

 stance, and immediately expel the whole of the liquid, — which becomes 

 at once absorbed by the asbestos, — and then, if necessary, gradually 

 move the heated bar forward, driving the substance towards the ignited 

 portion of the tube, until it shall have reached that point in the tube 

 where the temperature is just sufficient to cause the oxygen to take up 

 the* vapor in suitable proportion; indicated by the bubbles of oxygen 

 and carbonic acid, as will be described below : — a point as easily found 

 as to find, in the old process, the requisite temperature for proper dis- 

 tillation of the substance. When this is accomplished, which will 

 occupy but a short time, the heat in front of and behind the substance 

 being constant and uniform, no further manipulation of the heat is re- 

 tube of Bohemian glass, thus protected, may be used for a large number of analyses ; 

 and, indeed, become almost a permanent fixture upon the furnace. The asbestos 

 prevents the glass and metal from adhering together, — which is probably the chief or 

 only cause of breakage of wrapped tubes, — so that sudden cooling and re-heating 

 may take place with perfect security. It is important that the iron trough should 

 not extend much backward of that part of the tube where it is desired that the 

 combustion should take place, so that the temperature of the principal part of the 

 column of asbestos may remain under the control of the operator, by means of 

 the heated copper bar, or otherwise. 



Independent of the use of a metallic bar, as described above, or any novel ap- 

 pliance, the heat can be regulated by this furnace with as great, or even greater 

 nicety than by the use of coal. The partitions in this furnace, between the cocks, 

 are two inches apart ; so that the gas from one of the jets ignites about two inches of 

 the tube. To rely, therefore, alone upon the cocks for regulating the heat in burn- 

 ing the substance, would doubtless often lead to bad results ; but the heat may be 

 made to approach the substance in the most gradual manner, — next to that of con- 

 duction by a metallic bar, — by making use of a piece of thin brass plate, about 

 two inches long, and half an inch wider than the top of the furnace, the edges of 

 which are turned down against the sides. 



If this plate is laid on the wire gauze covering the furnace, and pressed down so 

 as to fit closely enough to prevent the gas from igniting under it, the gas escaping 

 from the cock underneath may all be made to burn at one end of the plate, and 

 to extend the heat along the tube as gradually as the plate itself is capable of being 

 moved. 



