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Mr. J. Joly. 



time to ensure that the thermometer and substance are uniformly at 

 one and the same temperature. This interval of course varies with 

 the nature and mass of the substance. In accurate work sufficient 

 interval must be left to leave no doubt on the matter, the room being 

 one not subject to sudden variations of temperature. When the 

 required interval has elapsed, the thermometer is read by a hand 

 lens, or better through a telescope. The temperature is noted down. 

 The burner is now lighted beneath the boiler, all hot gas and 

 steam being arranged to pass directly out of the room, as already 

 mentioned, and direct radiation carefully screened off from the 

 calorimeter. When the water is boiling, a second reading of the 

 thermometer is taken and noted down. The boiler is now suffered to 

 pass steam through the coupling-tube for about ten minutes, to 

 ensure that all is free from air and mist. During this time it is 

 better that the tube be directed so that the steam escapes up a flue 

 or out of the room. The interval is to be utilised in checking the 

 equilibrium of the balance, noting down the position of the rider, 

 and observing if the valve on the boiler is working freely and with- 

 out vibration. At the expiration of the interval, a third reading of 

 the thermometer is taken and rapidly noted. It is then carefully 

 withdrawn from the calorimeter, laid aside, and its tubulure stop- 

 pered with a little cork kept for the purpose. Everything is now 

 ready for admitting steam. The steam-pipe, with its nozzle held 

 upwards, is laid out along the slanting board which supports it 

 between the boiler and the calorimeter. The nozzle is then grasped 

 in the right hand, the steam- jet being still directed upwards. With 

 the left hand we turn the thumb- screw commanding the exit tubulure 

 at the bottom of the calorimeter, opening it to the full. The stopper 

 closing the entrance-way to the rear of the calorimeter is now to be 

 withdrawn, and then bringing the left hand back to the rubber 

 steam-tube, we pinch it sharply at a convenient point, some 20 cm. 

 below the nozzle, which, while the escape of steam is thus for the 

 moment prevented, is run into its position. The steam tube is 

 instantly released, and we give our attention to connecting by a 

 switch the platinum spiral with the storage-cells. This only takes 

 a moment, but by this time the steam is already pouring out at the 

 exit way. For thirty or forty seconds it should be permitted to flow 

 out freely ; what little condenses on the surrounding objects dries off 

 quickly, and does no harm. The air being thus completely cleared 

 out, the outflow of steam is moderated by closing the smaller tubulure 

 against the exit- way, and in from one to three or four minutes, 

 according to the nature and quantity of the substance, the weighing 

 may be effected. 



It will be at or.ce seen by the balance if the substance is completely 

 heated or not. If it is, it will be found that the vibration of the 



