ON PERCHROMIC ACID. 
55 
The balloon was half-filled with impure very acid peroxide 
of hydrogen, and placed in cold water. A tube connected 
with the balloon passed with its curved end under a gra- 
duated cylinder entirely filled with water. The apparatus 
so arranged was left for twenty-four hours, during which 
time not a bubble of gas passed into the cylinder. Upon 
this an accurately weighed quantity of bichromate of potash, 
in pieces of a nearly equal size, was conveyed through the 
cock into the liquid. As these pieces fell into the liquid they 
were surrounded with blue streaks, and bubbles of gas were 
disengaged, which passed into the cylinder. When the 
whole of the bichromate of potash had been added to the 
liquid, the amount of gas disengaged was read off after 
two hours' standing, and a second reading made after 
twenty-four hours; during this interval there was no per- 
ceptible increase of gas, although the liquid still contained 
peroxide of hydrogen. The chromium is no longer con- 
tained in the liquid as chromic acid when the evolution of 
oxygen has ceased, for the acid itself loses a portion of its 
oxygen during the effervescence, and is left as oxide. 0.5 
grm. bichromate of potash disengaged.— I. 152,11. 157^ 
III. 150, IV. 151, V. 150 cubic centimetres of oxygen, that 
is 1 equiv. of the salt to 4 equivs. of the latter, theory re- 
quiring 151 (equiv. of chromium = 310) or 155 (equiv. of 
chromium = 32S.) Now, since the chromium in 1 equiv. 
of the bichromate of potash, after it has been converted into 
the blue compound, and this again decomposed, is left be- 
hind as oxide, and consequently 1 equiv. of the salt parts 
with 3 equivs. of its oxygen, we may thence conclude that 
the peroxide of hydrogen, for every equivalent of the salt, 
adds 1 equiv. of oxygen to 6 in the chromic acid of the salt, 
so that the blue body obtains the composition Cr^ The 
reaction which gives rise to the perchromic acid may be 
expressed in the following manner : 
?(K0,Cr03 )-f HCI+0 = KCl + H04-Cr^ 
