Selenious Acid by Potassieum Permanganate. 53 
distinguishable. The exact point at which precipitation of the 
manganic hydroxide begins depends upon the dilution, acidity, 
and temperature of the solution. In experiments (1) and (2}, 
the permanganate was added to the cold solution at the first, 
but the liquid was heated after the addition of oxalic acid and 
before the final titration with the permanganate. The remain- 
ing determinations of the series were made in solutions kept 
hot throughout. 
TABLE I. 
[Se=s7 9 Oesr6: | 
Oxygen Oxygen 
equivalent of equivalent of 
permanga- oxalic acid 
SeO, taken. nate used. used. SeO, found. Error. 
erm, erm. erm. orm. erm. 
(1) 0°1000 0:03026 O:01s71 0°1010 0°0010+ 
(2) 0°1002 0:03038 0°01578 © 071014 0°0012+ 
(3) 0:0997 0°02634 0 01182 0°1008 O°;O011+ 
(4) 0°0999 . 0°02568 0°01122 0'1004 0°0005 + 
(5) 0°1000 0°02536 0:01077 O°1012 0°0012 + 
(6) 0°1000 0°03226 0°01765 O'1015 0°0015 + 
7) 0°1001 0'04455 0°02992 1°1016 00015 + 
A 0°2001 0°05448 0:02543 0°2018 O:;0017+ 
(9) 0°1997 0°05219 0:02318 0°2014 0:0017+ 
(10) 0:1997 0°05215 0°02318 0°2011 0°0014+ 
(11) OD 178 0°13215 O05 724 0°5203 0°0025 + 
(12) 0°5197 0°14105 0°06541 0°5252 0°0055 + 
An examination of these results develops the fact that the 
action proceeds regularly in the main under the conditions of 
experimentation, but that there is an apparent waste of per- 
manganate in the process. It was observed that the addition 
of a little permanganate beyond the exact amount necessary to 
produce the end-reaction occasioned the precipitation of man- 
ganese hydroxide, evidently, according to Guyard’s reaction, by 
interaction between the permanganate and the manganous sul- 
phate present. Plainly the amount of sulphuric acid present, 
which we kept purposely low to obviate the spontaneous 
decomposition of the permanganate, was not sufficient to pre- 
vent the ultimate formation of the hydroxide at the tempera- 
ture of action. The natural inference is that the difficulty in 
the determinations may have been due rather to an interference 
with the color reaction at the end of the oxidation process, due 
to the incipient tendency of the permanganate to act upon the 
manganous salt, than to direct loss of oxygen from the 
permanganate. If this is true, the obvious and simple remedy 
should be found in effecting the oxidation of the oxalic acid at 
the end of the process at a temperature so low that the inclina- 
tion of the permanganate and manganous sulphate to interact 
shall be diminished. Table II contains the record of experi- 
