324 
SELECTED ARTICLES. 
carbonate of iron (itself a hydrated peroxide) in muriatic acid, 
and throw it down again by liquor potassae. Our readers may 
recollect the rhyme: 
" The king of France, with twenty thousand men, 
Sailed up the Scheldt — and then sailed down again," 
Lastly, there are several preparations which are objectionable 
in every point of view. Tartar emetic is made by boiling 
cream of tartar with crocus of antimony. Hear what Berze- 
lius says of this method: " L'ancienne pharmacopee suedoise 
prescrit de faire bouillir, pendant une heure, du crocus avec de 
la creme de tartre, de filtrer la dissolution et de Pevaporer 
jusqua siccite, mais on obtient par ce moyen un produit dont la 
composition^ varie, et qui renferme quelquefois de la creme 
de tartre non saturee." 
Iodide of potassium is made by decomposing the iodide of 
iron by carbonate of potash. This is Baup's process; which 
is objectionable from the difficulty of avoiding an excess of 
potash on the one hand, or of suffering a considerable loss on 
the other, from the precipitation of peroxide of iron carry- 
ing down a large quantity of iodine. Mr. Ferguson has 
mentioned to us a process which he has been in the habit 
of pursuing, which is simple, cheap, and most extraordi- 
nary: by boiling carbonate of potash, iodine, and iron turn- 
ings together, with a proper quantity of water, iodide of 
potassium is formed; carbonic acid and oxygen escaping with 
a violent effervescence, and the iron turnings remaining un- 
touched. This is most strange, and evidently belongs to the 
operations of catalysis, lately generalized by Berzelius. We 
are told in the notes, (a fact with which chemists were hitherto 
unacquainted,) that iodide of potassium loses none of its weight 
by being subjected to the fire. Chloride of barium is directed in 
the Pharmacopoeia to be prepared by decomposing carbonate 
of baryta with muriatic acid; every one knows how much 
more rare a mineral witherite is than heavy spar. 
Sulphate of potash, the College order to be made by roast- 
ing the supersalt remaining after the preparation of nitric acid. 
