Volume 5

Elements of natural history, and of chemistry / being the second edition of the ... lectures ... first published in 1782 ... translated into English with occasional notes, and an historical preface by the translator [W. Nicholson].

  • Fourcroy, Antoine-François de, comte, 1755-1809
Date:
1788-1789
Catalogue details

Licence: Public Domain Mark

Credit: Elements of natural history, and of chemistry / being the second edition of the ... lectures ... first published in 1782 ... translated into English with occasional notes, and an historical preface by the translator [W. Nicholson]. Source: Wellcome Collection.

    156/408 (page 142)
    fun, faw, that a fliort time afterwards a blue co- lour was developed, which formed a precipi- tate until its total decompofition. A like mixture, preferved in a dark place, did not become blue, nor ^afford a precipitate even at the end of fevera! months : a ftrong heat pro- duces abfolutely the fame effedf. From thefe ex- periments, Mr. Berthollett fhews on what inac- curate information the procelTes recommended for purifying the alkaline pmffiates were found- ed : for, faid he, they were decompofed for the moft part, inftead of depriving them of a portion of Prufiian blue, which chemifts pre- tended was only accidentally mixed with it. As the prufliate of potafli is a triple fait, the PiTilfian acid has only a very flight adhefion to the potafli, and is feparated by all the other acids. In proportion as the foreign acid unites to the porafli, part of the Pruflian acid unites to the oxide of iron, forming Prulfian blue ; and the other is volatilized in the ftate of acid, or reduced to its principles. The iron which is precipitated by the al- kaline prufliates, retains, according to Mr. Ber- thollett, a confiderable portion of thofe falts : it may be deprived of them by repeated wafli- ings. Thefe lixiviums contain the alkalis, combined with a fmall portion of Pruffian acid ; and the prufliates, with excefs of alkali, are not earned off until the excefs of acid in the foliition of iron is carried off by the firfh wafliings; for the latter lixiviums precipitate iron