Imágenes de páginas
PDF
EPUB

POCKET ENCYCLOPEDIA

OR A

DICTIONARY

OF

ARTS, SCIENCES,

AND

POLITE LITERATURE

COMPILED FROM THE BEST AUTHORITIES

BY

EDWARD AUGUSTUS KENDAL.

Embellished with Copper Plates designed and engraved by

EMINENT ARTISTS.

SECOND EDITION.-Corrected and much enlarged.

IN FOUR VOLUMES.

VOL. II.

LONDON:

PRINTED FOR LONGMAN, HURST, REES, ORME, AND CO.,

J. HARRIS, SCATCHERD AND LETTERMAN, PEACOCK
AND BAMPTON, WILKIE AND ROBINSON, AND R.
BALDWIN.

[blocks in formation]

Salola 11-14

POCKET ENCYCLOPEDIA.

1172 -- RAF

COLD. Cold, in a relative sense, signifies the sensation which accompanies a transition of the fine vessels of the human body from an expanded to a more contracted state. In an absolute sense, it signifies the cause of that transition ; or, in general, the cause of the contraction of every substance, whether solid or fluid, in nature. Great degrees of cold are produced by mixing together substances which dissolve rapidly. The reason of this will appear when it is recollected that in the conversion of solid bodies into fluids caloric is always absorbed. Mixtures to produce artificial cold are generally made of neutral SALTS (which see) and of snow: or of neutral salts, diluted acids, and powdered ice or fine flaky snow. The following tables given to the public by Mr. Richard Walker of Oxford will exhibit at once all that is important on this subject.

In order to produce these effects, the salts employed must be fresh crystallized, and newly reduced to very fine powder. The vessels in which the freezing mixture is made should be very thin, and just large enough to hold it, and the materials should be mixed together as quickly as possible.

To produce the very low degrees of cold, the materials in the first column are to be cooled previously to mixing, to the temperature required, by mixtures taken from either of the following tables. Tbis obe Servation chiefly applies to the third table.

VOL, II,

[ocr errors]
« AnteriorContinuar »