36 Improvements in Physical Science (Jan. 
oxyprussic acid, formed by mixing chlorine-and prussic acid, has 
likewise been examined by Gay-Lussac. He has shown it to be a 
coinpound formed by the union of equal volumes of chlorine gas 
and cyanogen gas, and in consequence has given it the name of 
chloro-cyanic acid. ‘This acid is a colourless liquid, having a very 
strong smell, and acting on the eyes and nose nearly as strongly as 
ammonia. It reddens litmus; is not combustible. The specific 
gravity of its vapour is 2111. Its solution in water does not preci- 
pitate nitrate of silver nor barytes-water. Alkaline bodies seem to 
combine with it ; but the instant an acid is poured on the compound, 
the chloro-cyanic acid is decomposed, and carbonic acid and am- 
monia formed. Gay-Lussac has rendered it probable that in this 
case the whole chloro-cyanic acid and the portion of water decom- 
posed are resolved into 
1 volume muriatic acid, 
1 volume carbonic acid, 
]_ volume ammoniacal gas. 
G6. In the historical introduction published iu the Annals of Phi- 
losophy at the beginning of last year (vol. v. p. 25), I gave an 
account of ferrureted chyazie acid and sulphureted chyazie acid, 
two new compounds discovered by Mr. Porrett. Since that time 
this ingenious chemist has subjected these acids to a new analysis. 
The results whiclr he obtained are as follows. Ferrureted chyazic 
acid is composed of 
Prussic acid...... £ ISS EBITD Ss oe Sh atotis 
Black oxide of iron... 86°21 ...... 1 
100-00 
Sulphureted chyazic acid is composed of 
Prussic acid, 3. Mieke on, OLS coo ce only atom 
Sulphur...... pierced 55 Ee, Sam eyo seeds 
100-0 
I should not be surprised if these two acids were in reality com- 
pounds of cyanogen with iron and sulphur ; that is to say, cyanides 
of iron and sulphur. As some of Mr. Porrett’s data were erroneous, 
it is obvious that his conclusions cannot be quite correct. 
7. Chromic Acid.—In the year 1812 an elaborate set of experi- 
ments on chromic acid by Mr. Brandenburg, an apothecary at 
Polotzk, in Russia, was read before the Imperial Academy of 
Sciences at St. Petersburgh. It was published in the Russian lan- 
guage in the technological Journal of the Academy, vol. x. 1813. 
The original German copy is inserted in Schweigger’s Journal (vol. 
xiii. p. 274). The object of the experiments is to show that the 
substance called chromic acid by Vauquelin is not a simple combi- 
nation of chromium and oxygen; but that it always contains a 
portion of the acid employed ‘to separate it from the alkaline body 
with which it was combined, and that to it only it owes its acid 
