480 Hinman— Volumetric Determinations by Chromic Acid. 
Of course bodies like ferric and cupric salts that are reduced 
by stannous chloride must be absent and the solution must not 
be so concentrated that the green of the chromic chloride ob- 
scures the iodo-starch blue. Stannous chloride has had the 
reputation of changing rapidly on standing, but I have found 
it quite stable, when properly protected from the air, as the fol- 
lowing results show : 
March * 10 cc. potassium bichromate required, ; ep ec. stannous chloride. 
“ Aai a“ “ ““ . Joucy a sé 
April 16, a“ “cc 4“ “ 7-734 ce : “ 
May 21, “ “c “ “ i V4 “ i“ 
The following determinations can be made by means of 
chromic acid. The chromates of lead, barium, and bismuth 
n be accurately precipitated, barium from an ammonical 
ion, the others from an acetic solution. The determina- 
tion of lead is given as an exam 
Twenty-five cc. of a solution of lead acetate, fifty cc. of 
which gave 0°5908 gram lead sulphate, were diluted with water 
and a little acetic acid, heated to boiling in a small beaker and 
10 ce. standard bichromate solution added. The precipitate 
of lead chromate was filtered off after standing a few minutes, 
washed, and the excess of chromic acid determined in the fil- 
trate. The quantity of stannous chloride required was 0-20 ce. ; 
other experiments gave 0°21, 0.21, 0°20, and 0:20, by calcula- 
_ tion from the amount of lead sulphate there should have been 
peguiran 0°19 ce. being an error of one or two parts in about 
fa known quantity of bichromate is added to acid solu- 
tions of arsenious or antimonious acids they will be oxidized to 
can then be determined. Twenty-five cc. of a solution of 
arsenious acid, containing 5-2675 grams per liter, plus 10 cc. 
standard bichromate solution, required 1:36, 1°35,.1°33, and 
1-35 cc. of stannous chloride. If the arsenious acid had been 
pure only 1°22 cc. stannous chloride would have been required 
instead 1°85. In other words the arsenious acid contained 
about one and four-tenths per cent impurity. The only anti- 
mony compound I happened to have at hand was tartar emetic, 
but tartaric acid in that seemed to interfere with the reaction 
to a certain extent so that the results were not satisfactory. 
Sulphuric acid can be determined as follows: ‘To a slightly 
acid solution of a sulphate heated to boiling is added a small 
excess of a solution of barium chromate in hpdrochilorie acid, 
barium sulphate is precipitated ; then the solution is neutral- 
ized with ammonia which precipitates the remaining barium 
chromate, the precipitates of barium sulphate and chromate 
are filtered off and the chromic acid determined in the filtrate 
is equivalent to the sulphuric acid in the original solution. 
