OF ARTS AND SCIENCES. 



23 



A 



and by multiplying observations possibly to the one bunflredth of a 

 degree. In his admirable investigation of the boiling point of sul- 

 phur at different temperatures, the observations of temperature are 

 undoubtedly accurate to this extent; but Regnault's own discussion of 

 these observations plainly indicates that there must have been un- 

 known or accidental causes influencing his experiments, which render 

 the results uncertain to at least one degree ; and the boiling point of 

 sulphur is still in doubt to this extent. It should be added, however 

 that there are only a very few boiling points which are 

 known more accurately ; for, even when within the range 

 of a mercury thermometer, an observation of a boiling point, 

 to be accurate to a tenth of a centigrade degree, requires ( 

 an attention to circumstances which is seldom bestowed on 

 such observations. 



The glass thermometer-bulb used in our experiments is 

 represented in the accompanying figure (Fig- 1) of one half 

 the actual size in its linear dimensions. The longer stem 

 was made of thermometer tube, and a shorter stem was 

 added to the opposite end of the bulb in order to facilitate 

 the cleaning, drying, filling, or emptying of the interior, all 

 of which was easily accomplished by the aid of a Bunsen 

 pump. The shorter stem was of course sealed after the 

 bulb had been dried and made ready for use, and before it 

 was immersed in the medium whose temperature was to be 

 measured. After an equilibrium had been established at 

 this unknown temperature, T'°, the protruding end of the 

 longer stem was sealed, and at the same time the height of 

 the barometer, H, was noted. The bulb was then taken to 

 a room of uniform temperature provided in the laboratory 

 for gas analysis, and, after being mounted on a convenient 

 support, the end of the stem was broken off under mercury, 

 and the apparatus left to itself for a time to secure a per- 

 fect equilibrium of temperature. This temperature, T°, 

 was then observed, by means of a standard thermometer 

 hanging near the bulb ; also the height, h, to which the mercury had 

 risen in the bulb, was measured by a cathetometer ; and in addition 

 the height, H', of a barometer (hanging in the same room) was noted. 

 Closing now the open stem with the finger, the bulb was quickly in- 

 verted and the containing mercury drawn out into a tarred vessel and 

 weighed (nipping off the extreme end of the shorter stem for the pur- 

 pose). This gave the weight, xo. Lastly, the bulb and stem having 



\l 



Fig. 1. 



