356 



Mr. J. Joly. 



balance. The hemispheres of the calorimeter are then run up on the 

 rail from each side of the balance and closed around the carrier. 

 They are placed so that the wire passes freely through the aperture 

 provided. A thermometer graduated to the tenth pai*t of a degree 

 Centigrade is next inserted in the tubulure opening to the front of the 

 balance, so that its bulb projects well into the sphere. The tunnel- 

 shaped covering is placed in position, and the piece of zinc and the 

 carrier counterpoised. The balance is sensitive to half milligrams. 



We assume that the thermometer indicates closely the temperature 

 of the zinc after the lapse of about an hour. At the end of that time 

 the boiler is heated up, and steam passed briskly through the leading 

 tube to heat it throughout. This tube is of a length permitting the 

 boiler to be placed at a safe distance from the calorimeter. The ther- 

 mometer, where it projects from the sphere, is now read, in doing 

 which it is necessary to remove the front half of the tunnel for a 

 moment. The temperature indicated is 10" 73° (corrected at Kew), 

 the last number by estimation. 



The thermometer is now withdrawn and the admission pipe slid 

 quickly along the rail up to the calorimeter, the leading tube being 

 pinched for a moment during this brief operation. Steam is now 

 flowing rapidly into the calorimeter ; in a few seconds it begins to 

 escape at the exit tube to the far side of the balance. When it is 

 seen to come out freely a valve on the boiler is opened, and so much 

 steam diverted directly into the air that it now issues but slowly from 

 the exit tube of the calorimeter. 



The balance being let down on its bearings, weights are added till equi- 

 librium obtains. If the substance is quite heated this weight remains 

 absolutely adequate, if not the weight is again adjusted when no further 

 increase is apparent. After the space of about one minute we find the 

 balance continues to vibrate equably ; we observe it for some five or 

 ten minutes, and see that there is no change in the equable vibrations 

 of the pointer. We are sure then that the total weight of con- 

 densation is obtained. It is found to be 0'798 gram. 



A thermometer — also reading to tenths — inserted in a little tubulure 

 provided for it on the boiler, reads 100*25° (corrected at Kew). 



The experiment is now completed, and it only remains to make a 

 couple of corrections on the value obtained as the weight of con- 

 densed steam before calculating the specific heat of the piece of zinc. 

 Two corrections are necessary — 



(1.) The bucket has, by a previous experiment, been found to 

 condense 0*031 gram of water over a range of 87*90°. The range in 

 our experiment is 100*25° — 10'73° = 89*52. Therefore the deduction 

 for the bucket is — 



0-031 + 89-52-87-90 x Q.Q31, 

 87*90 



or 0*0315 very nearly. 



