252 PROCEEDINGS OF THE AMERICAN ACADEMY 



far as I am informed, having been mostly confined to the combustion 

 of the residual carbon of highly carbonaceous substances, after the 

 other decomposition products, containing the hydrogen, had been burnt 

 at the expense of oxide of copper. 



By a very simple device I entirely obviate the danger of explosion ; 

 viz. the combustion tube is closely packed with asbestos, or other inert 

 substance,* and yet so loosely as to leave free passage for gases through 

 the interstices. The packing of the tube requires some care. This, 

 however, may be readily accomplished, giving great uniformity to the 

 mass of asbestos, by having the latter carefully broken into small, loose 

 pieces, which are gradually added to the tube, and arranged in position . 

 by means of a stiff iron wire. Little attention need be had to the pack- 

 ing of the centre of the tube, as this will come right of itself, if the 

 packing against the sides is properly done. It will be found convenient 

 and expeditious to turn the tube continuously in the hand, and cause 

 the end of the iron rod to follow around against the sides of the tube, 

 placing the asbestos, by gentle taps, alongside its inner surface, so that 

 only very small open spaces may be seen. 



In the experiments which I have made I have generally had about 

 ten or twelve inches in length of the tube filled with asbestos. As the 

 combustion takes place within a very short space, it seemed at first that 

 the tube might be reduced considerably below the ordinary length ; it 

 was found, however, that shortening of the tube below a certain limit 

 made it difficult to control the distillation of volatile substances and pre- 

 vent too rapid combustion ; it being essential in this, as in other pro- 

 cesses, that the combustion should proceed slowly, and with a good 

 degree of regularity ; otherwise it would be difficult to regulate the 

 supply of oxygen to meet the demand of the burning substance. By 



* I have used only asbestos in my experiments thus far, and in every instance 

 with perfect success. Quartz sand, selected with care as to the size of the grains, 

 had suggested itself, on account of greater convenience in filling the tube, as it 

 would properly arrange itself on simply being poured into the tube. It would, 

 however, be liable to the objection, that any jarring of the tube, while lying upon 

 the combustion furnace, would be likely to settle the particles more closely together, 

 and form a channel along the top, in which an explosion might take place which 

 would spoil the analysis. I therefore prefer asbestos to anything which I have 

 thought of; and any apparent inconvenience in preparing a tube with this substance 

 will pass into insignificance, if the precautions which I advise for protecting the 

 tube from breakage are observed, as tlien the same tube may be made to last for a 

 long time. 



