Hinman— Volumetric Determinations by Chromic Acid. 479 
During the last few years I have had occasion to make a 
large number of determinations of the quantity of sulphur in 
coal gas, and have often wished for some process of determin- 
ing sulphuric acid less tedious than the ordinary gravimetric 
ne by barium sulphate and more accurate than the volumet- 
reduced by quite a number of reagents. I had previously 
found a delicate test for chromic acid in the acid solution of 
starch paste and potassium iodide. It remained to be seen if 
the blue color disappeared as soon as the chromic acid was all 
reduced. I found that of the ordinary reducing agents only 
an acid solution of stannous chloride produced Ps result, 
even when a large excess of acid was present. I found that 
as 
allreduced. It was finally found desirable to boil the bichro- 
mate solution And cool it out of contact with the air; when 
this was done the quantity of water present made no difference 
in the amount of stannous chloride required. The following * 
ch 
nearly tothe neck. The flask is closed with a stopper agit 
which passes a glass tube, at the end of which is a rubber v 
opening outward. The contents of the flask are boiled for 
eget Segoe and then cooled; the valve preventing the access 
OF ® A few centimeters of h drochlotie acid are added and 
and potassium iodide added to the contents of the flask pro- 
duces a dark blue color which is to be removed by the cau- 
tious addition of stannous chloride. The exact point is easy 
to hit as at last the color changes rapidly with a small addition 
of the chloride. The following determinations were made in 
this manner, a standard solution of potassium bichromate con- - 
taining 14-761 grams per liter being used 
K,Cr,0, SnCl, Ratio. 
25 ec. req. 19°26 ce 770% 
10°04 
10 7°72 772 
10 7°73 “773 
3 2°32 773 
