Identifier: 2573052R.nlm.nih.gov
Title: A system of chemistry : comprehending the history, theory, and practice of the science, according to the latest discoveries and improvements ; illustrated with copper plates
Year: 1791 (1790s)
Authors: Dobson, Thomas, 1751-1823, printer Scot, Robert, 1744?-1823, engraver Vallance, J. (John), 1770-1823, engraver Thackara, James, 1767-1848, engraver
Subjects: Chemistry
Publisher: (Philadelphia) : Extracted from the American edition of the Encyclopedia now publishing, by T. Dobson, at the stone-house, in Second-Street, Philadelphia
Contributing Library: U.S. National Library of Medicine
Digitizing Sponsor: Open Knowledge Commons, U.S. National Library of Medicine

View Book Page: Book Viewer
About This Book: Catalog Entry
View All Images: All Images From Book
Click here to view book online to see this illustration in context in a browseable online version of this book.

Text Appearing Before Image:
be applied to any ufefulpurpofe ; afterwards with an imperfect neutral fait,called greeti vitriol, which is applicable to feveral pur-pofes where the pure acid itfelf could not be ufed ;but ftill the acid by itfclf is not to be had without avery troublefome operation. ^ Though this acid adheres very flrongly to iron, it is Diflimtio*capable of being expelled from it by fire; yet not «f vitriolicwithout a very violent and long-continued one. If acidiromwe attempt to diflil green vitriol in a retort, it fwells C0PFr«-and boils in fuch a manner by the great quantity ofwater contained in its cryftals, that the retort will al-mort certainly crack ; and though it fliouldnot, the faitwould be changed into an hard rtony mafs, which thefire could never fufficiently penetrate fo as to cxtri- tcate the acid. It niuft therefore be calcined previousto the diftillation. This is befl done in fiat iron-pans,let over a moderate fire. The fait undergoes the wa- t«ry ( ji i. M I S T R\ Plate C\\\\l\
Text Appearing After Image:
A A /,/ my- Pra&ice. CHEMISTRY. 89 Vitriolicacid andits combi-nations. 621 Preferva-tives ofwood. 622Rectifica-tion. tery fufton, fSee Fusion) j after which it becomesopaque and wnite. By a continuance of the fire, it be-comes brown, yellow, and at laft red. For the pur-,.pofes of diftillation, it may be taken out as foon as ithas recovered its folidity. The dry vitriol, being now reduced to powder, is tobe put into an earthen retort, or rather long neck(a kind of retort where the neck iffiies laterally, thatthe vapours may have little way to afcend), which itmay nearly fill. This retort mull be placed in a fur-nace capable of giving a very ftrong heat, fuch as themelting furnace we have already defcribed. A largereceiver is to be fitted on; and a fmall fire made inthe furnace to heat the vefiels gradually. Whitefumes will foon come over into the receiver, whichwill make the upper part warm. The fire is to bekept of an equal degree of (Irength, till the fumes be-gin to difappear,

Note About Images