Chap. 3.] Apparatus for evaporating liquids in vacuo. 495

might be beneficially applied to large blowing tubes, and thus contributeto the same result.

There are other useful applications of these blowing instruments. Oneof our first attempts was to employ them as Substitutes for the expensiveair-pumps worked by steam-engines, employed in evaporating sirups andrefining sugar by Howard’s vacuum plan.

No. 221. Apparatus for evaporating liquids in vacuo.

We fitted up a very strong old still, (No. 221) three feet m diameter andabout the same in depth. A jacket of copper was fitted to its lower partso as to form a double bottom. The discharging pipe passed through thejacket, and was closed by a valve V. Steam being conveyed into thejacket heated the liquid within the still, but instead of taking steam fromthe boiler expressly for this purpose, we made use of that by which thevacuum was produced. The open end of a blowing tube was insertedmto the jacket as represented in the cut, and the vacuum tube B connectedby a cock to the neck of the still. C the steam cock and pipe leading tothe boiler. D a pipe that conveyed the surplus steam from the jacketmto the chimney. The orifice of the vacuum pipe within the blowing onewas three-eighths of an inch diameter, and the annular space around it forthe passage of the steam was the same as in No. 217. At the first trialwith this apparatus, 25 gallons of sirup were put into the still through thefunnel, and the cock shut. The steam cock C was then opened, and in afew moments the mercury in the gauge rose 15 inches, but in eight minutesfeil to 10 inches, the fall being occasioned by the evolution of vapor in thestill. The steam in the boiler was raised higher, until the mereury roseto 16 inches; but after the Operation had been eontinued about half anhour it commenced rising, and was at 18 inches when the experiment wasclosed. On another trial 32 gallons of sirup were poured in, and whenC was opened the mercury rose to 22 inches, but in ten minutes feil to 17.In half an hour it began slowly to rise, and in fifteen minutes reached to20 inches, at which height it remained when the concentrated sirup waswithdrawn.

Had a double tube like No. 220 been used, the vacuum might probablyhave been carried to 28 or 29 inches, and the Operation performed in muchless time. The experiment however shows how small a tube can with-