On the Steam Calorimeter. 



245 



of a cork ; this is removed when steam is first admitted. When the 

 calorimeter is thoroughly filled it is replaced by a second cork, pierced 

 by a short brass tube having a bore of about 7 mm. The diameter 

 of this exit tube might also, with advantage, be reduced from that 

 shown. 



The platinum spirals used in drying and warming the suspending 

 wires at their points of exit are in series, of the same length and fine- 

 ness. The automatic adjustment at the orifices is applied, and, indeed, 

 alone renders the differential arrangement workable. There is no 

 difficulty in effecting the most accurate observation of weight. 



The body of the calorimeter is cylindrical in form — a form used for 

 its stiffness and inexpensiveness. The ends of the cylinder are closed 

 by hemispherical caps of thin, spun copper. These have a swelled 

 flange fitting smoothly over the ends of the cylinder, and are further 

 kept in their places by two thumbscrews, fixed in the box covering 

 the calorimeter, one at each end, and so located that when the box is 

 in position and the screws screwed in, they will bear against the 

 hemispheres. Owing to the shape of the calorimeter, it is necessary 

 to shelter the carriers from drip by guards or umbrellas of thin Dutch 

 metal, sprung on two projecting wires into the tubulures of the 

 orifices, so that they can be removed and dried. 



To allow of weights being placed on either side of the balance, 

 the ordinary stirrups must be removed. The arrangement shown on 

 the figure works well. Weights may be laid on or taken off the little 

 inner pans without swinging the suspending wires supporting the 

 carriers. 



In conclusion, it may be worth remarking that many laboratory- 

 instruction, or even lecture-table experiments of interest may be 

 readily shown with the differential calorimeter. Thus the law of 

 atomic heats is illustrated by placing quantities of two simple bodies, 

 proportional to their atomic weights, in the calorimeter, and equili- 

 brating by weights placed in the upper pans. On admitting steam, 

 the equilibrium of the balance will (theoretically) remain undisturbed. 

 Similarly Wcestyn's law of the constancy of specific heats of bodies 

 in the free and combined states might be illustrated by placing the 

 free elements in the proportions of chemical composition on one carrier, 

 and an equal weight of the combined elements on the other. 



The application of the vapour calorimeter to the determination of 

 latent heats of vaporisation is very probably possible. I regret that 

 neither this application of it, nor the allied question of the employment 

 of other vapours besides that of water, can be considered here, the 

 study of the capabilities of the steam calorimeter and a couple of its 

 applications having occupied my time up to the present. 



