M. TECHNOLOGY. 



523 



before mentioned by means of the rubber ring or cork. In 

 order to insure the perfect tightness of the joint between the 

 flask and the tube, upon whicli the success of the operation 

 of freezing is largely dependent, the stop-cock upon the tube 

 is closed, a small quantity of water is poured between the 

 cork and rim of the glass (to render any subsequent leak- 

 age visible), a few strokes of the pump are made to exhaust 

 partially the acid receiver, and the stop-cock is turned on. 

 The effect of this preliminary manipulation is to firmly attach 

 the flask to the tube by atmospheric pressure, and insure a 

 perfectly air-tight joint. The pump is now worked rapidly 

 for a few minutes, w^hen the water in the flask begins to 

 evaporate rapidly, and at last bursts into violent ebullition. 

 The vapor evolved is drawn through the receiver containing 

 the acid, which at once absorbs and condenses it. Very soon 

 a few filaments of ice will be observed to form in the water, 

 and the pumping is to be continued for a few minutes longer, 

 after which a stop-cock connecting the pump with the re- 

 ceiver is closed and the flask left on the tube. In fifteen or 

 tw^enty minutes afterward the water will be found to be 

 frozen throughout. The flask can then be removed and an- 

 other substituted, and if the stop-cock between the flask and 

 the receiver was closed previous to the removal of flask No. 

 1, the vacuum in the receiver will have been preserved, and 

 much of the preliminary pumping may be dispensed with in 

 the case of flask No. 2. 



The theory of this operation is the same as that of the fa- 

 miliar lecture-room experiment of freezing water by its own 

 evaporation. In the case of M. Carre's device, the rapid evap- 

 oration of the water effected with the pump by relief of press- 

 ure is materially aided by powerful absorptive qualities of 

 the sulphuric acid in the receiver; and in order to insure 

 better contact of the acid and vapor, an ingenious apparatus 

 called the agitator is provided by the inventor, which stirs 

 up the acid during the motion of the pump. This agitator 

 consists of a rocker furnished with paddles, and extending 

 the length of the receiver, the motion of the rocker being ob- 

 tained by means of a lever attached to the pump-handle. 

 The apparatus is carefully constructed, so as to avoid the en- 

 trance of acid either into the flask or the pump, so that the 

 employment of the acid need afford no inconvenience to the 



