134 Apparatus for freezing Water by the aid of Sulphuric Acid. 



best order possible ; for the purpose of obviating leakage through 

 the cocks associated with the instrument, I closed the hole in the cen- 

 tre of the air pump plate by a screw, and for a receiver made use of 

 a bell glass with a perforated neck furnished with a brass cap and a 

 female screw, by means of which one of my valve cocks was attach- 

 ed. A communication between the bell, and the chambers of my 

 pump, was established through the valve cock and a flexible lead 

 pipe, in a mode analogous to that already described in the account 

 of the valve cock. In this way I succeeded in preserving the vacu- 

 um, longer than when the cocks of the air pump were employed in 

 the process ; and accomplished the congelation of water by means 

 of the vacuum, and sulphuric acid. 



Latterly, I have used an apparatus which is represented by the ad- 

 joining figure, in which a brass cover is made to close a large glass 

 jar so as to be quite tight. In operating, the bottom of the jar was 

 covered with sulphuric acid, and another jar with feet, also supplied 

 with acid enough to make a stratum half an inch deep on the bottom, 

 was introduced as represented. The bottom of the vessel last men- 

 tioned, was, by means of the feet, kept at such a height above the 

 surface of the acid in the outer jar, as not to touch it. Upon the sur- 

 face of the glass vessel, a small piece of very thin sheet brass was 

 placed, made concave in the middle, so as to hold a small quantity 

 of water. 



The brass cover was furnished with three valve cocks, one com- 

 municating with the air purop, another with a barometer guage, and 

 the third with a funnel supplied with water. Under these circum- 

 stances, having made a vacuum on a Saturday, I was enabled to 

 freeze water situated on the brass, and to keep up the congelation till 

 the Thursday following. As the water in the state of ice evaporates 

 probably as fast as when liquid, during the night the whole quantity 

 frozen would have entirely disappeared, but for the assistance of a 

 watchman whom I engaged to supply water at intervals. At a max- 

 imum I suppose the mass of ice was at times about two inches square, 

 and from a quarter to a half an inch thick. The gradual introduc- 

 tion of the water, by aid of the funnel and valve cock, also of the 

 pipe represented in the figure, by which it was conducted to the cav- 

 ity in the sheet brass, enabled me to accumulate a much larger mass 

 than I could have produced otherwise. The brass band which em- 

 braces the inner jar near the brim, with the three straps proceeding 



