3/4 



On the Determination of the 



[Nov. 



upon so small a proportion, to obtain an exact result was scarcely 

 possible : but the nature of our apparatus, and the great pains 

 which we bestowed on the experiments, induce us to think that 

 the following resuits are not very remote from the truth. 



The air, when it came out of the gazometers, was mixed with 

 a great quantity of vapour, and then passed through a serpentine 

 tube surrounded with water, kept all the time of the experiment 

 at the temperature of 102-2°. In that serpentine it deposited 

 its excess of vapour, so that we may consider it as perfectly 

 saturated with vapour at the temperature of 102*2°. The current 

 was then heated in the steam tube, and passed through the calo- 

 rimeter, as in the other experiments. 



To prevent the air from depositing water while passing 

 through the calorimeter, it was necessary to keep it always above 

 the temperature of 102° : for this purpose it was sufficient to 

 heat the air in the room where the calorimeter was to the tem- 

 perature of about 86°. The air thus saturated with vapour made 

 the calorimeter stand stationary at 106*34°, the ambient air being 

 S5-64°. Hence the effect produced was 106*34° — 85-64° = 

 20-/°; frond which it is necessary to subtract 3-6°, the effect 

 produced by the gas pipe. There remains : 7*1° for the effect 

 produced by air saturated with moisture at the temperature of 

 102-2°. Now this air entered the calorimeter at the tempera- 

 ture of 207' 14°, and came out at the temperature of 106*3 1°. 

 Hence it cooled 100-8° to produce this effect. 



As soon as this experiment was finished, there was substituted 

 for the vessel in which the air became saturated with vapour, a 

 serpentine tube surrounded with a mixture of pounded ice and 

 salt, which, continued during the whole of the experiment below 

 5°. Tilings being thus circumstanced, the experiment was 

 repeated. The current of air thus dried lost in passing through 

 the calorimeter 102*42° of heat, and kept the calorimeter sta- 

 tionary at 104-72°, the amiient air being 85*64°. The effect 

 produced by this dry air, subtracting the heat communicated by 

 the gas tube, was 15*48°. By the rule of proportion it ought to 

 have been 15*12°, if the current of air had lost 100 8° in passing 

 through the calorimeter, as was the case with the current of 

 moist air in the preceding experiment. 



The difference between these two experiments, made exactly 

 in the same way, is 1/~*1° — 15*12° = 1*98°. Therefore l*98 c 

 is the effect produced by the vapour. 



During the continuance of this experiment the barometer 

 stood at 29-906 inches ; and the tension of the vapour, at 

 102-2°, is, according to Dalton's table, 1-988 inch. Of conse- 

 quence, in the air saturated with vapour, the volume of air was 

 to that of vapour in the ratio of 15*0 to 1. The effect of elastic 

 fluids on the calorimeter being, in the same circumstances, pro- 



