106 Prof. Regnault on the Specific Heat of some Simple Bodies. 



sequence of too much evaporation during a lengthened experi- 

 ment, the tube B is somewhat larger towards the upper part. 



A current of air is driven through the tube efg, either by 

 means of an aspirator adapted to the tubulure c, or by a force- 

 pump, or by a pair of bellows applied directly to the tube efg. 

 As I have at my disposal large reservoirs in which a force-pump, 

 moved by a machine, compresses the air to several atmospheres 

 in a very short tine, the operation is very simple ; a large reser- 

 voir of compressed air communicates with the tube efg. By 

 regulating the stopcock r, a more or less rapid current of air 

 traverses the ether of the tube B, and escapes saturated with 

 vapour through the tubulure ac: the temperature rapidly sinks 

 in consequence of evaporation. When the ether is near the desired 

 temperature, which is seen by a thermometer whose bulb dips in 

 the ether, the stopcock is turned so as to stop the cooling, and 

 with a little practice the temperature may be maintained station- 

 ary as long as is desired. The thermometer T, whose bulb is in 

 the basket M, is necessarily behind that which is immersed in 

 the ether ; but the two thermometers gradually approximate when 

 the current of air is suitably regulated. The basket M is only 

 immersed in the calorimeter when equilibrium is almost established. 



The temperatures obtained by this apparatus are not so low as 

 those obtained by means of freezing-mixtures of ice and crystal- 

 lized chloride of calcium : thus, when the external temperature 

 is +20°, it is difficult to keep the ether stationary at a lower 

 temperature than —12° C; under the same circumstances the 

 temperature only sinks with bisulphide of carbon to —-8°: 

 but, from the readiness with which low temperatures are kept 

 stationary for a long time, more accuracy is obtained in the 

 determinations. 



By a precisely similar arrangement, the temperature of a liquid 

 can be gradually lowered and kept stationary at any desired point. 

 I have often used it to determine the point at which a liquid 

 solidifies when this solidification takes place between — 15° 

 and + 10°. The inside tube A is closed at the bottom (fig. 3) ; 

 the liquid is placed in it along with a thermometer which indi- 

 cates the temperature and serves as an agitator. By means of a 

 current of air, the temperature of the ether is lowered gradually 

 and as slowly as required; the thermometer immersed in the liquid 

 sinks in a like degree to the point at which solidification begins; 

 its temperature then becomes stationary. To invert the process, 

 the current of air is diminished or completely stopped. The 

 temperature of the ether then rises ; the liquid should be conti- 

 nually agitated with the thermometer, and it should be ob- 

 served whether, when it commences to rise, the solidified part 

 has entirely resumed the liquid state. 



