120 CONGELATION OF MERCURY. 



begins. The bulb is then wrapped up in a little cotton wool, 

 or what is better, in a little bag of line fleecy hosiery j and after 

 being dipped into ether, the apparatus is quickly laid over the 

 |-eceiyer, which is exhausted as rapidly as possible. In two or 

 three minutes the temperature sinks to about 45 below 0, at 

 which moment the quicksilver in the stem suddenly descends 

 with great rapidity, (in consequence of the remarkable con- 

 traction which the mercury in the bulb undergoes {n congeal- 

 ing) to a distance corresponding to between 300 and 400 de- 

 grees. This, however, seldom happens to that extent, because 

 the descent of the mercury is often impeded by the freezing of the 

 column itself at the entrance of the bulb, before the congelation 

 within the bulb is completed. 

 ^he facts par- If it be desired to exhibit the mercury in its solid state, cotn- 

 tIC V ar y 6 ' a " mon tubes may be used, which should be broken instantly after 

 being removed from the pump. I have frozen in this way 

 bulbs of an elongated shape, about an inch in length, and near an 

 inch in diameter. The pump I have used for these expeii- 

 ments is one of a small size j* the gage of which stands at about 

 a quarter of an inch, when the exhaustion is pushed to its utmost 

 extent. I have occasionally succeeded in this experiment, 

 when the temperature of the room, as well as that of the ether, 

 was about 50° $ but the certainty of success is much increased 

 by operating in a room, the temperature of which does not 

 exceed 40°, and by previously reducing the temperature of the 

 ether. I have been in the habit, in making this experiment, 

 of inclosing sulphuric acid within the receiver, as in Mr. Les- 

 lie's process, as it has appeared to me to promote the evapora- 

 tion of the ether, and the production of cold ; but the experi- 

 ment has also succeeded without the assistance of sulphuric 

 acid. 

 Variationof the The same experiment may be varied by first dipping the bulb 

 experiment. G f the thermometer, surrounded with cotton wool or flannel, 

 into water, and after freezing this by means of the pump, pour- 

 ing a few drops of ether upon the frozen bulb, and exposing it 

 again to the effect of exhaustion. This plan has sometimes 



Made by Mr. Bate, instrumen t maker in the Poultry. 



succeeded 





