WOULFES APPARATUS. Under various forms, and with several modifications, this apparatus is much employed in chemical operations.
The arrangement, first described by its inventor in the Philosophical Transactions,' is inconvenient in form ; we shall therefore give a description of one of several improvements to which it has been subjected. A retort a (Jig. 1.) is attached and secured by means of lute to the first receiver b, which has a right-angled glass tube, open at be's, ends, fixed into its tubulure ; and the other extremity of the tube is made to terminate beneath the surface of distilled water, con tained, as high as the horizontal dotted line, in the three-necked battle c. From another neck of this bottle a second pipe proceeds, which ends, like the first, under water contained in a second bottle d.
To the central neck a straight tube, open at both ends, is fixed, so that its lower end may be a little beneath the surface of t,he liquid. Of these bottles any number may be employed that is thought necessary. The materials being introduced into the retort, the arrangement completed, and the joints secured in the manner to be described, the distillatiou is begun. The condensable vapour collects in a liquid form in the balloon b, while the evolved gas passes through the vent tube, beneath the surface of the water in c, which continues to absorb it till saturated. When the water of the first bottle can absorb no more, the gas passes, uncondensed, through the second right-angled tube into the water of the second bottle, which, in its turn, becomes saturated. Any gas that may be produced, which is not absorbable by water, escapes through the vent-tube e, and may be collected, if requisite, in an air-jar filled with and inverted in water in the pneu matic trough. This is represented in fig. 2 by f, f, and g.
Supposing the bottles to be destitute of middle necks, and con sequently without the perpendicular tubes, the process would be liable to be interrupted by an accident ; for if, id consequence of diminished temperature, an absorption or condensation of gas should take place in the retort a, and of course in the balloon kit must necessarily ensue that the water of the bottles c and d would be forced by the pressure of the atmosphere into the balloon, and possibly into the retort, which might cause a dangerous explosion ; but, with the addition of the central tubes, a sufficient quantity of air rushes through them to supply any accidental vacuum. This inconvenience, however, is still more effectually obviated by Welther's tube of safety (jig. 2) b, which super sedes the expediency of three necked bottles. The apparatus being adjusted, a small quantity of water is poured into the funnel, so as to about half fill the ball b. When any absorption happens, the fluid rises in the ball till none remains in the tube, when a quantity of air immediately rushes in and supplies the partial vacuum in a. On the other hand, no gas can escape under ordinary circumstances ; because any pressure from within is instantly followed by the formation of a high column of liquid in the perpendicular tube, which resists the egress of the gas.
We have .already observed that various modifications of this appa ratus have been proposed, an account of which may be seen in different chemical treatises ; the above description is taken almost entirely from Dr. Elements.'