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PHIPPs’S JOURNALe 587
afcend with the vapour, and aét on the ftill-head and worm pipe, impregnating the water
with metallic falts of the moft pernicious quality.
«© 4, The fpace occupied by the ftill, ftill-head, and worm-tub, renders the ufe of
them in moft cafes totally impracticable on board fhips. Add to this, their wearing out
fo faft on account of the caufes above mentioned, the great expence of the apparatus,
with the hazard of the ftill-head being blown off, and the inconveniences thence arifing.
“6, The ufe of,ingredients, which though omitted in fome experiments in {mall,
were neverthelefs erroneoufly confidered as effential to the making {ea-water iweet and
palatable by diftillation.
*©6, The inconvenience of a cumberfome apparatus, calculated only to be event-
wally ufeful in unexpetted diftrefs for water, but con{tantly occupying a great deal of
room in a fhip, too neceflary for the ordinary purpofes to be {pared for that object.
<‘ Having fpecified the principal defects of the feveral methods hitherto prdpofed for
making fea water frefh, it will be proper before ftating the advantages of Doctor Ir-
ving’s method, to confider briefly the principles of diftillation in general, and the che-
mical analyfis of fea water.
«© Water in an exhautfted’ receiver, rifes in vapour more copioufly at 180° of Fahren-
heit’s thermometer, than in the open air at 212°, which may be confidered as its boiling
oint.
ee It therefore follows, that any compreffion upon the boiling fluid cheeks the vapour
in rifing, and confequently diminifhes the quantity of water obtained. ‘This is clearly
exemplified in the fteam-engine, where the confumption of water in the boiler is very
inconfiderable, in comparifon to what would happen if the compreflion arifing from the
throat pipe, and valve of that machine was taken off, and the preflure of the atmofphere
only admitted. But by the reftraint of that valve, the vapour becomes hotter, and in-
creafes in rarity and elafticity ; qualities effential to the purpofes of the engine, although
the reverfe of thofe which ought to take place in common diftillation, For the columns
of vapour fhould be removed from the boiling fluid as faft as they afcend, without fuf-
fering any other refiftance than that of the atmofphere, which, in the ordinary bufinefs
of diftillation, cannot be prevented.
“¢ The impropriety of the common procefs of diftillation, will appear evident by com-
paring it with the above principles and facts.
«« In the common method of diftillation, the whole column of vapour from a {till of
whatever fize, after afcending to the ftill-head, muft not only find its paflage through a
pipe of fcarce an inch and half diameter ; but defcend contrary to its fpecific gravity
through air which is fifteen times its weight, in fpiral convolutions: a courde fo ex-
tremely ill adapted to the progrefs of an elaftic vapour, that frequently the {till head is
blown off withincredible violence, owing to the increafed heat and elafticity of the va-
pour confined by this conftruction. In the mean time the external furface of the pipe
communicates heat to the water in conta& with it, which, inftead of being entirely car-
ried off, mixes the furrounding fluid, and heats the whole, rendering it unfit for con-
denfing the vapour within; efpecially when it is confidered that the fubftance of the
pipe is at leaft a quarter of an inch thick.
«- From what. has been faid, it is plain, that the quantity of diftilled water will be
leffened in proportion to the refiftance made to the afcent of the vapour, while the dif-
ficulty of condenfation will be greatly augmented, in confequence of the increafed heat
and elafticity of the vapour. But thefe difadvantages, however great, refpecting the mode
of diftillation, give rife to another evil of a {till more important nature, as affecting the
diftilled fluid with a noxious burnt tafte or empyreuma ; occafioned by the vapour,
4F 2 highly
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