54 Gooch and Clemons—Selenious Acid, etc. 
ments in which this precaution was taken. The entire process 
of oxidation, which was otherwise similar to that of the previous 
experiments, was brought about between the temperature of 
75° C. at the beginning and 50° C., or even a little less, at the 
end. The end-reaction was in every case sharp and the final 
color was permanent for several minutes at the least. 
TABLE II. 
Oxygen Oxygen 
equivalent to equivalent to 
permanganate oxalic acid 
SeO. taken. used. used. SeO. found. Error. 
orm. orm. erm. erm. erm. 
(13) 0:1000 0°03506 0°02065 0°1001 0°0001+ 
(14)  0°1000 0°03419 0°02073 0°1004 0°0004 + 
(15) 0°1000 0°03706 0°02255 0:1007 0°0007 + 
(16) 1000 0°03853 0°02422 0°0994 0°0006 — 
(17) 0°1000 0°05512 0°02065 0°1005 0:0005 + 
(18) 0:2000 0°06124 0°03256 0°1992° 0°0006 — 
(19) 02011 0°06069 0°03177 0°2008 0°0003 — 
(20) 0°2004 0°06072 0°03177 .0°2010 0°0006 + 
(21) 0°2020 0°06083 0°03185 0°2012 0°0008 — 
(22) 0°2038 0°06106 0°03185 0°2028 0°0010— 
These results are evidently an improvement upon those of 
the first series of experiments, and are fairly satisfactory so far 
as concerns the estimation of the amounts of selenium dioxide 
discussed. The determination of large amounts of selenious 
acid by this method is somewhat less advantageous than it 
would be if the reduction of the permanganate proceeded far- 
ther in the first action. One hundred cubic centimeters of a 
standard solution is as much as can be conveniently handled in 
a single process of titration, and that volume of decinormal per- 
manganate (which is about as strong as the standard solution 
should be when accurate work is expected) is capable of oxi- 
dizing about 0°258'™ of selenium dioxide. 
The process which we recommend consists, in brief, in the 
addition of standard potassium permanganate to the solution 
of selenious acid containing not more than five per cent of its 
volume of strong sulphuric acid, the introduction of standard 
oxalic acid until the liquid clears, and the titration of the excess 
of oxalic acid by permanganate, at a temperature not much 
exceeding 50° or 60° OC. The permanganate and the oxalic 
acid should be standardized under similar conditions of acidity 
and temperature, and for a standard of final reference we prefer 
pure crystallized ammonium oxalate. 
We have made experiments in which the initial oxidation of 
the selenious acid was made in alkaline solution, but inasmuch 
as the amount of permanganate required for the oxidation is 
about three times as great as that needed in the acid solution 
the treatment in alkaline solution is practically inferior. 
