OP ARTS AND SCIENCES : MARCH 8, 1864. 259 



oxygen at that point, and thereby diminish the hability to loss from 

 diffusion of gases or vapor backward into the drying apparatus, which 

 is always too liable to occur when the posterior end of the combustion 

 tube is not sealed. 



As an additional precaution against loss from this source, this con- 

 necting tube is packed with asbestos in the same manner as the com- 

 bustion tube ; and during the combustion is heated with one of Bunsen's 

 burners. In case vapor of the substance should reach this tube, not- 

 withstanding the above precaution against it, it could not reach the 

 drying apparatus as such ; but would be immediately decomposed, and 

 the carbonic acid formed would at least stand a good chance of being 

 carried forward, and prevent a loss in the determination of the carbon. 

 The heating of this connecting tube may be superfluous for the object 

 above described (a point which I have not yet taken the time to deter- 

 mine) ; but it certainly has the good effect of heating the oxygen, and 

 thus preventing the condensation of liquid at the cork in the end of 

 the combustion tube. 



In the performance of an analysis, the first step should be to expel 

 the moisture from the combustion tube, while hot, by passing through 

 it, for some time, a stream of dry air from the gasometer.* The tube 

 should then be filled with oxygen, before the substance, if volatile, is 

 added ; as otherwise particles of unburnt substance might escape during 

 the displacement of the air, and occasion loss. The absorbing appa- 

 ratus, having been previously weighed, is then attached, and, if the 

 excess of oxygen employed is to be saved, the oxygen again admitted 

 to expel the air from the absorbing apparatus. The connection is then 

 made with the receiver G, if used, and the tightness of the joints tested 

 by turning down the tube B, so as to partially exhaust the apparatus. 



* The necessity for this may be entirely obviated, after the first analysis, and 

 much time saved and uncertainty avoided, by connecting the anterior end of the 

 combustion tube, at the close of a day's operations, with a set of stationary drying 

 tubes of ample capacity, which may stand back of the furnace out of the way, com- 

 munication with which is established by means of a flexible tube. Or, better, a 

 movable tube may be attached by means of a screw to the opening in the top of the 

 gasometer, extending to the top of the upper reservoir, so that water cannot enter, 

 and then, by simply turning the cock underneath, communication would be opened 

 between the surrounding air and the combustion tube, through the intervening 

 drying apparatus. At the close of work the anterior end of the combustion tube 

 should then be tightly corked, the fire extinguished, and the tube allowed to cool in 

 diy air. It would thus be always ready for immediate use. 



