368 



Mr. J. Joly. 



slight as possible. The half chambers being closed, steam is admitted 

 at the top of the apparatus, the expelled air escaping at the bottom 

 through a tube which passes through the base of the instrument. 

 In plan it will be seen that the steam is admitted by a forked or 

 branching tube at two tubulures, which in elevation are seen to be 

 cut back so as to afford a ready seat for the supply pipe, and also that 

 the latter when placed in position may conduce to bind closer the 

 half-chambers. The steam pipe is supported further and retained in 

 position on a light pillar springing from the tripod base. To its seat 

 on this pillar it is clipped by a spring bearing against the centre of 

 the fork, but so that it may readily be laid in its position. A little 

 tubulure is also provided for conveniently taking the temperature by 

 inserting a thermometer.* At other times this tubulure is closed by 

 a little cap (not shown in the drawing). Two half -cylindrical plugs 

 of plaster of Paris, notched at their meeting faces, serve as before to 

 pass the wire depending from the balance,, which is supposed to rest 

 upon a shelf placed above the apparatus. 



Within the outer shell of the calorimeter an inner shield of very 

 slight brass is provided, similar in shape, and capable of a rotational 

 motion of about 60° about its vertical axis. This is effected by 

 attaching it to a tube which rotates smoothly in the exit-tube at the 

 base of the calorimeter. It is worked by a stud projecting through a 

 horizontal slot cut in the latter. The shield is made in halves, and 

 opens on hinges affixed to the rotating tube. Above, each half of the 

 shield is perforated, so that when in one extreme position it receives 

 within it all the entering steam, but on being rotated 60° no longer 

 admits steam directly, the perforations being then, turned away from 

 the entrance tubulures. 



When it is desired to close the exit-tube of the calorimeter, a stop 

 is pressed in through a horizontal slot in the tube.. Water condensed 

 from the steam by radiation from the calorimeter is received in a little 

 trough placed beneath the tripod stand. 



The apparatus is worked as follows : — 



The carrier being suspended at the right height on the wire from 

 the balance, and the substance being arranged upon it, the calorimeter, 

 with its inner and outer cases drawn back, is moved under and then 

 closed upon it. The inner case is now rotated so that the calorimeter 

 is thus still further closed, and also one of the apertures of the shield, so 

 placed that a thermometer may be passed through the small tubulure 

 into the interior of the calorimeter. To guard the calorimeter against 

 sudden changes of temperature while the thermometer is assuming 



# The effect of scale parallax in reading thermometers may conveniently be 

 avoided by bringing tbe scale into coincidence with its reflection on tbe mercury 

 thread of the thermometer. The way of doing this is easily acquired after a couple 

 of trials. 



