Elements of chemistry : including the applications of the science in the arts . kettle with a safety valve,water may be raised to 3 or 400° without ebullition: but theinstant that this great pressure is removed, the boiling com- i^sSSSLmences with prodigious violence. The facility with which liquids boil under reduced pressure isfrequently taken advantage of in the arts, in concentrating liquorswhich would be injured in flavour or colour by the heat necessaryto boil them under the pressure of the atmosphere. Mr. Howardapplied this principle in concentrating the syrup of sugar, which plliJIili/
Elements of chemistry : including the applications of the science in the arts . kettle with a safety valve,water may be raised to 3 or 400° without ebullition: but theinstant that this great pressure is removed, the boiling com- i^sSSSLmences with prodigious violence. The facility with which liquids boil under reduced pressure isfrequently taken advantage of in the arts, in concentrating liquorswhich would be injured in flavour or colour by the heat necessaryto boil them under the pressure of the atmosphere. Mr. Howardapplied this principle in concentrating the syrup of sugar, which plliJIili/i- apt to be browned when made to boil under the usual thus boiled syrup at 150°, applying heat to it in a pan co-vered by an air-tight lid, and pumping off the air and steam from the upper part 1 For the most recent minute determinations of the boiling point of water, under varia-tions of atmospheric pressure, see the memoir of M. Regnault; Ann. de Chimie, &c, 3 serie,t. xiv. p. 196. A simple portable apparatus for the experiment is also described there. 5. GO VAPORIZATION, of the pan by means of a steam-engine. This was the most essential part of Inspatent process, by which nearly the whole of the loaf sugar consumed in this countryhas been manufactured for many years. In the same apparatus vegetable infusions may be inspissated, or reduced to thestate of extracts, for medical purposes, with great advantage. When an extract isprepared in the ordinary way, by boiling down an infusion or expressed juice in anopen vessel under atmospheric pressure, a considerable and variable proportion of theactive principle is always destroyed by the high temperature and exposure to theair. But the extract is not injured when the infusion or juice is evaporated at alow temperature, and without access of air, and is generally found to be a more activemedicine. The temperatures at which different liquids are converted into vapour are exceed-ingly various; but other things remaining
Size: 1296px × 1927px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1850, bookpublisherphila, bookyear1853
