Combi7iation of Bodies voith Oxygen. 329 



order to ascertain positively that the whole of the heat had 

 been obtained. 



The longer period of time occupied in these experiments 

 rendered the corrections for the cooling and heating influence 

 of the air of more importance than in the former observations. 

 To determine with absolute accuracy the value of these cor- 

 rections, under the varying circumstances of each experiment, 

 would have been extremely difficult. It has therefore been 

 my endeavour so to arrange the experiments, that the amount 

 ot correction to be applied in each case may be very small; 

 so small, indeed, that tiie application of an imperfect approxi- 

 mation may be practically sufficient. From the effects of fric- 

 tion, the proximity of the person of the observer and other 

 causes, the rate of heating was always greater than the rate of 

 cooling for equal differences between the temperature of the 

 air and of the apparatus; and for the same reasons, the latter 

 was found to maintain a stationary temperatin-e only when the 

 thermometer in it indicated a temperature about 0°'3 C. higher 

 than that of tlie surrounding air. If we represent by a the 

 difference between the temperature of the air and of the ap- 

 paratus, the correction V lor the gain or loss of heat sustained 

 by the apparatus during m minutes will be expressed by the 

 formula^ 



V=+?K(a + 0°-3) Q^-0025. 



The values of V given by this expression agree within the 

 ranges of temperature which occurred in these experiments, 

 very closely with the direct results of observation. 



The usual time which elapsed between the observation of 

 the initial and final temperatures was sixteen minutes ; and in 

 such cases it was assumed that the apparatus was at the 

 minimum temperature during one and a half minute, at the 

 maximum during eight minutes, and during the intermediate 

 period at the temperature of the air. In other cases, where 

 the combination took place more quickly, the corrections were 

 made on the assumption that the apparatus was at the minimum 

 point during one minute, and at the maximum during one-half 

 of the whole time occupied by the experiment. 



Carbon and Oxygen. 



The carbon was employed in the form of wood-charcoal. 

 It was purified by the method of M. Dumas from all oxidable 

 mailers; first by ebulliiion in strong nitro-mi'riatic acid, and 

 afterwards by exposure I'or several hours at a strong red heat 

 to the action of dry chlorine gas. To expel all volatile com- 

 pounds, it was finally exposed to a strong white heat under a 

 layer of charcoal. The earthy impurities, together with a 



