On the Steam Calorimeter. 



2m 



the tube and boiler ; air entering and flowing along one side of the 

 pipe, steam issning along the other. On narrowing the opening of 

 the tube, so that a well-defined current of steam having the full 

 section of the tube issued, the effect disappeared. The foregoing- 

 method of providing for the exit of the surplus steam is defective 

 and unsafe. It is preferable to use a non-return valve of some sort. 

 I find the simple arrangement shown on the boiler in PL 7 (scale 

 one-tenth) very effective. It is simply a balanced flap-valve, meeting 

 the vertical exit-tubulure on a ground edge brought fine, so as not 

 to stick with precipitated water. The counterpoise to the weight of 

 the flap can be placed at discretion in one of several notches near the 

 end of the beam, so that the pressure may be increased or diminished. 

 To keep this valve from falling into vibration, the pivot on which it 

 turns bears at one end against a screw, which may be tightened so as- 

 to retard a little the oscillatory motion of the beam. The pressure 

 maintained should be small, as pressures appreciably in excess ox 

 atmospheric pressure interfere with the working of the calorimeter. 

 The valve should therefore be so set that it just falls shut readily 

 when steam is not issuing. This, according to measurement, in the 

 case of che valve used by me corresponds to rather less than a pres- 

 sure of 1 mm. of water. The material of the boiler is copper, tinned 

 within. The burner is a large " solid flame " of Fletcher. 



Method of Carrying out an Experiment. — I will suppose the calori- 

 meter dry and cold, and ready for the introduction of the substance. 

 This is placed on the carrier which hangs within the calorimeter 

 dependent from the balance. Having adjusted the substance 

 centrally on the carrier, and so that there is no fear of water dropping 

 from any protruding point of the substance over the edge of the 

 catch water, and so escaping estimation by the balance, the ther- 

 mometer for taking the initial temperature of the substance is to be 

 inserted in its tubulure. This is done now, before closing the calori- 

 meter, in order to see that its bulb does not strike against the 

 substance or the stirrup of the carrier, and that it is inserted suffi- 

 ciently far to be well over and close to the substance. The substance 

 should now be roughly counterpoised by placing weights in the right- 

 hand pan of the balance, and before the final adjustment of the 

 balance, the calorimeter closed. On now finally adjusting the equi- 

 librium of the balance, we observe if the wire swings freely through 

 the several orifices through which it passes. The weight placed oil 

 the right-hand pan affords W, the weight of the substance, if, as 

 should be arranged, equilibrium be previously obtained between the 

 carrier and the pan. It is necessary also to see that the lower orifice 

 of the calorimeter is closed with the wooden stop, and that the 

 entrance- way for the steam-pipe at the back is also stoppered. 



After these preparations the calorimeter must be left a sufficient 



VOL. XLVII. T 



