168 Dr. H. F. Weber on the Specific Heat of 



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w 11 w fl) w„...wj 



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were determined were briefly as follows : — 



The amounts by weight, G, of the substance to be examined 

 were determined, by means of an (Ertling's balance, to within 

 0*1 to 0*03 per cent, of the total weight ; a greater exactness was 

 unnecessary, since the values of T and W could not be deter- 

 mined to within less than 0*1 percent, of their absolute amount. 

 The values T^ T lf T 2 , . . . T n and W„ W 2 , . . . W n were not de- 

 termined by the same means throughout. Within the limits 

 —80° to +300° the temperature was determined directly by 

 means of thermometers, and the corresponding quantities of heat 

 measured by the ice- calorimeter; for high temperatures, 500° to 

 1000°, both of these values were calculated from the calorimeter- 

 readings. The detailed description of both methods is as fol- 

 lows. As means for obtaining a range of temperature from low 

 to high points under a red heat, solid carbon dioxide, freezing- 

 mixtures of snow and salt, and an oil- bath were used. By regu- 

 lating the gas-flame and by constantly stirring the liquid, the 

 temperature of the oil-bath could be kept so nearly constant, that 

 in an interval of 15 to 20 minutes it did not alter more than one 

 degree. Two test-tubes 10 centims. long, placed one within the 

 other, the space between them being filled with cotton-wool, 

 formed the vessel in which the substance was heated. After 

 the substance had been placed in this vessel, a plug of cotton- wool 

 was inserted as a stopper, and the vessel was immersed in the 

 cooling (or heating) liquid for a full hour. The temperature of 

 the solid carbon dioxide and of the freezing-mixture remained 

 during that time perfectly constant. Small variations in the 

 temperature of the oil-bath were, as far as possible, prevented 

 by regulating the gas-flame. At the expiry of one hour the 

 final temperature was determined, the heating-vessel seized in 

 the hand, removed from the bath (or cold mixture), brought into 

 a horizontal position, and moved as quickly as possible towards 

 the opening of the calorimeter standing close by. At the mo- 

 ment when the opening of the heating- vessel came very near 

 the opening of the calorimeter the plug of cotton-wool was with- 

 drawn, and by a quick jerk the heated substance was thrown 

 into the calorimeter, so that without touching the walls of the 

 instrument it should fall into the receiving vessel. After a little 

 practice the heated substance could be deposited in the calori- 

 meter not more than two seconds after the vessel containing it 

 was removed from the bath. During this interval of time the 



