1819.] Scientific Intelligence. 389 



tainmg it, have already been mentioned. The degree of exhaus- 

 tion is~ of course judged of by the column which is supported in 

 the attached mercurial gauo-e ; and I think it will excite some 

 surprise when it is stated, that although no pump is employed, 

 yet that column is often at a height of 28 inches during rapid 

 ebullition. In fact, it is common to operate with a column not 

 two inches less than the barometer of the day, and at such times 

 the temperature of the boiling fluid is below 100° Fahr.; often at 

 95° ; and I am satisfied that by certain improvements, this tem- 

 perature may be reduced to less than 90° in the ordinary process 

 of manufacture. The vessels employed in the apparatus first put 

 up were two : the one of cast-iron polished in its inner surface, 

 serving as the evaporating pan, and situated in a water-bath, 

 may be called a still. The head of it leads into a second vessel, 

 which is a large copper sphere, about three times as large as the 

 other, and surrounded at pleasure by cold water; it may be 

 called the receiver. In the pipe which connects these two, is a 

 large stop-cock, by which their communication with each other 

 can be suspended. The manner of setting it to work is this : 

 The juice, or infusion, is introduced through a large opening 

 into the polished iron still, which is then closed, made air-tight, 

 and covered with water. The stop-cock which leads to the 

 receiver is also shut. In order to produce the vacuum, steam is 

 allowed to rush through the copper sphere until it has expelled 

 all the air, for which five minutes are commonly sufficient. This 

 is known to be effected by the steam issuing uncondensed. At 

 that instant the copper sphere is closed, and the steam shut off, 

 and then cold water admitted upon its external surface. The 

 vacuum thus produced in the copper sphere, which contains 

 four-fifths of the air of the whole apparatus, is now partially 

 transferred to the still by opening the intermediate stop-cock. 

 Thus four-fifths of the air in the still rush into the sphere; and 

 the stop-cock being shut again, a second exhaustion is effected 

 by steam in the same maimer as the first was; after which a 

 momentary communication is again allowed between the iron 

 still and the receiver : by this means four-fifths of the air 

 remaining after the former exhaustion is expelled. These 

 exhaustions repeated five or six times are usually found sufficient 

 to raise the mercurial column to the height before mentioned. 

 The water-bath in which the iron still is immersed is now to be 

 heated until the fluid that is to be inspissated begins to boil, 

 which is known by inspection through a window in the appara- 

 tus, made by fastening on air-tight a piece of very strong glass ; 

 and the temperature at which the boiling point is kept up is 

 determined by a thermometer. Ebullition is continued until the 

 fluid is inspissated to the proper degree of consistence, which 

 also is tolerably judged of by its appearance through the glass 

 window. I prefer making, for a single operation, as much juice 

 or infusion as will keep the apparatus employed for nearly the 



