- bP Se Tag 
Se a ee ak 
~~ <. Quantity of Heat evolved from Atmospheric Air. A7 
_. When the air attains*a certain pressure in this reservoir, it 
is allowed to discharge itself, by means of a communicating 
pipe,.into an- engine which works expansively through a valve 
so constructed, as to permit of being arranged to cut off 
pte 
_.. There were several appendages to the machinery employed in 
so 
would not be used in a practical application of the principle. 
Among them is the vessel, I. This was a reservoir of a former ex- 
periment, and was used, in this instance, to separate the water of 
injection from the condensed air, the former of which 
| through the cock, K, while the latter proceeded through the pipe, 
| L, into the reservoir, C. It is mentioned, and represented in the 
4 drawing, in order that all the circumstances attending the experi- 
. ments may be understood. 
| As a means of measuring with precision the pressure of air in 
the reservoir, a gauge consisting of a glass tube, closed at the up- 
| per end, having a length of twelve inches, and an internal diam- 
i eter of a quarter of an inch, was used. After filling this tube 
| with dry air, and inserting it through the upper surface of the 
reservoir, into a cup of mercury, in communication with the air 
_ within the reservoir, it was found to act as a convenient manom- 
Bae ane 2 : , 
| distegarding these sources of error, and probably some in charg- 
ing the tube with mercury, it was found to be a valuable instru- 
Ment; its indications were not only more easily attained, but 
Were more accurate than those of the steam indicator, or common 
__ +e standard which I have relied upon, in conducting the ex- 
Petiments of this research, for determining a measure of heat, is 
the assumed quantity required for the conversion of a pound of 
1ce into water. In the absence of any experiments of my own 
- 
