On the Method of Condensation in Calorimetry. 355 



porting" the substance contained within the spbere. But one-half this 

 covering is shown in the plate. It is borne upon the two outside rails 

 of the girder, which between the rails is filled in with mahogany. The 

 tunnel serves to isolate the calorimeter completely from the mechanism 

 of the balance, and thus arranged lean detect no errors due to escape 

 of heat. The apparatus might, however, also be arranged to stand 

 beneath the balance, the balance being supported on a shelf, and a 

 wire carried down from it to the calorimeter. 



The little screws seen at the feet of the standards bear against the 

 upper surface of the rail, enabling the standards to be adjusted for the 

 accurate meeting of the ground joints. This is effected once for all. 

 For smooth working the standards are clipped sideways against the 

 rail by spring straps. Thumbscrews on top of the standards permit 

 axial motion of the several parts, enabling the hemispheres to be 

 adjusted for the free passage of the wire. The steamways are insu- 

 lated from the standards by split rings of hard wood. Beneath the 

 sphere, and accommodated by a gap in the central rail, a little vessel 

 is placed for catching the water which drips from the sphere during 

 experiment. The correct position of the girder is secured by means of 

 a plate fixed to the floor of the balance, and provided with recesses to 

 receive the feet of the girder. The girder is thus placed in position, 

 and may be lifted in and out as required, without necessity of any 

 readjustment. 



The support for carrying the substance being experimented on, and 

 the bucket for catching the condensed vapour dropping from it, are 

 shown about full size in Plate 6. It is best to have these made of 

 platinum. The conical bucket shown to one side of the carrier, and 

 which, when in use, rests on the little claw beneath the latter, is of 

 thin platinum foil. The rest is of platinum wire. This design secures 

 slightness and strength — over 100 grams may be placed on the cross 

 wires — and supports the substance so that it is freely exposed to the 

 steam on all sides, while the bucket beneath can be conveniently 

 removed for cleaning and drying. Buckets made of silver foil quickly 

 tarnish, owing to impurities in the steam. They prove less constant 

 in calorific capacity than those of platinum.* 



Method of Making an Experiment. 



In exemplification of the manipulation involved in making an 

 experiment, I describe one made on cast zinc. The piece of zinc is 

 probably nearly pure. It weighs 48'300 grams. 



About an hour before we make the experiment it is placed on the 

 carrier, which depends by a fine platinum wire from the hook of the 



* All the apparatus described in this paper is the workmanship of Yeates, of 

 Dublin, and leaves nothing to be desired. 



