454 Mr. W. Rosenhain on an 



is cut off, and the tap (n) (figs. 2, 3, and 4) is opened. This 

 establishes free communication between the gas in the com- 

 bustion-chamber and the water o£ the calorimeter through 

 the small pipe (o). As the water-level in the calorimeter 

 when rilled for use is at (p p), the tap (n) is only just above 

 water-level, and the whole of the pipe (o) is immersed in the 

 water ; any gas escaping by this pipe is thus thoroughly 

 cooled. When the tap (n) is open, the water is only pre- 

 vented from entering the combustion-chamber by the ball- 

 valve (k). Such a valve was found necessary to prevent the 

 water from rushing into the combustion-chamber whenever 

 the combustion slackened. At those times the gases in the 

 combustion-chamber would cool and contract so rapidly that 

 the oxygen supply could not keep up the pressure, and, in 

 the absence of a valve, the water often entered and ex- 

 tinguished the combustion. The presence of the valve, 

 however, necessitates a by-pass, which is provided by means 

 of an opening (g) in one of the tubes (;), which is normally 

 closed by a stopper with a long handle projecting above the 

 water-level. It will be seen that no stirring arrangement is 

 used, as it is found that the vigorous bubbling of the gas 

 from the many small holes (m) stirs the water most efficiently. 



The combustion is started in the first instance by means of 

 xi platinum wire heated electrically. An insulated wire 

 passes down the tube (t) from the terminal (s) ; the other 

 terminal is formed by the oxygen inlet-tube (/), whose upper 

 end carries the terminal (u). Both the oxygen inlet-tube 

 -and the lead-tube (t) pass through the upper clamping-plates 

 by means of stuffing-boxes which allow the heating-wire to 

 be moved about and also admit of the adjustment of the 

 position of the oxygen inlet. 



The stand (v) (fig. 4) is provided with a bayonet-joint 

 similar to that on the base of the calorimeter-vessel for the 

 purpose of holding the combustion-chamber when removed 

 from the calorimeter. For the introduction of the sample of 

 coal at the commencement of an experiment, the chamber is 

 placed on this stand and the wing-nut (w) is loosened ; this 

 allows the lamp-glass and its attachments to be lifted off and 

 replaced when the coal has been put in place. The com- 

 bustion-chamber, having been screwed up, is then removed 

 from the stand and put into place within the calorimeter- 

 vessel, the water being only poured in after this has been 

 done. 



The length of time occupied by a combustion varies with 

 the conditions : with a sample of coal in the shape of a 

 briquette, weighing about 1J grammes, and containing 7 per 



