452

EVAPORATION.

the steam only 224, the same boiler in the same time would produce a diminished quan-tity of steam, in the proportion of 12 to 30 ; or to produce the same quantity the boiler ortubular surface should be enlarged in the proportion of 30 to 12. In general, however,steam boilers employed for this mode of evaporation are of such capacity as to give anunfailing supply of steam.

I shall now illustrate by some peculiar forms of apparatus, different systems of eva-poration. Fig. 381 explains the principles of evaporating in vacuo. A b represents

a pan or kettle charged with the liquor to be evaporated. The somewhat wide orifi*®c, secured with a screw-plug, serves to admit the hand for the purpose of cleaning llthoroughly out when the operation is finished; h is the pipe of communication with thesteam boiler; 6 is a tube prolonged and then bent down with its end plunged into th eliquor to be evaporated, contained in the charging back, (not shown in the figure). H ISa glass tube communicating with the vacuum pan at the top and bottom, to show by theheight of the column the quantity of liquid within. The eduction evaporating P : P ec is provided with a stop-cock to cut off the communication wh.cn required, i is a tH * ,efor the discharge of the air and the water from the steam-ease or jacket; the reiV;t:rr : ’.t'”'E is best formed of thin copper tubes about 1 inch in diameter, arranged zig-zag or spn •like the worm of a still in a cylinder. The small air-tight condenser f, connected witthe efflux pipe /"of the refrigerator, is furnished below with n discharge cock g> ® nsurrounded by a cooling case, for the collection of the water condensed by the refrige r "ator. In its upper part there is a tube k , also furnished with a cock, which communicawith the steam boiler, and through which the pan A nis heated.

The operation of this apparatus is as follows : after opening the cocks c, /,and before admitting the cold water into the condenser e, the cock of the pipeopened, in order that by injecting steam it may expel the included air; after winchcocks k and g are to be shut. The water must now be introduced into the conden-^and the cock b opened, whereon the liquid to be evaporated rises from the chargingthrough the tube b, and replenishes the vacuum pan to the proper height, as shown ^the register glass tube H. Whenever the desired evaporation or concentration is e jed, the cock c must be closed, the pipe 1c opened, so as to fill the pan with steam,then the efflux cock a is opened to discharge the residuary liquor. By shutting ^cocks a and It, and opening the cock 6, the pan will charge itself afresh with liquor,the operation will be begun anew, after 6 has been shut and c opened. ation-

The contents of the close water cistern f, may be drawn off during each °P e *" . 0 fFor this purpose, the cock / must first be shut, the cold water is to be then run o ^

the condenser g, and k and g are to be opened. The steam entering by k man fce

water flow, but whenever the steam itself issues from the cock g, this orifice m ..immediately shut, the cock f opened, and the cold water again introduced, w . or ,the condensed water that had meanwhile collected in the under part of the reli g

flows off into the condenser vessel r. Since some air always enters with