176 
hyposulphite and sulphite are in our possession, and we 
can form two equations from which both the unknown 
quantities x l and y x can easily be calculated. 
Let x x = grammes iodine corresponding to Na 2 S 2 0 3 present, 
y v = grammes iodine corresponding to Na 2 S0 3 „ 
A. = the quantity of iodine which the unit requires for 
testing with starch. 
= grammes Na 2 S0 4 which the unit yields on perfect 
oxidation, 
x 1 + y l = k 
2Na 2 S0 4 
and 
then 
Na 2 S 2 0 3 
Na 2 S 2 0 3 
or 2Na 2 S0 4 
X-i "t 
Na 2 SQ 4 
Na,SO, 
Na 2 S0 3 
21 
. V\ = B 
x x -f 
Na 0 SCb 
21 
which gives us 
*i = 
21 
3Na,S(X 
■ B - JA 
yi = -f A - 
21 
B. 
3Na 2 S0 4 
To get the result as grammes Na 2 S 2 0 3 and Na 2 S0 3 it is only 
, , Na 2 S 2 0 3 . , Na 2 S0 3 _ 
necessary to multiply x x by — = — , and y x by — ~ T — . From 
this we find x = grammes Na 2 S 2 0 3 = 
2Na 2 S 2 0 3 
B 
21 
Na 2 S 2 0 3 
y = grammes Na 2 S0 3 = 
3Na 2 S 0 4 31 
= -741784 B- -414698 A. 
2Na 2 S0 3 , Na 2 S0 3 
B 
31 3Na 2 S0 4 
= •661417 A - -295775B. 
Care must of course be taken that the dilution while 
titrating is sufficient, and at least two titrations ought to 
be made. 
If besides hyposulphite and sulphite, sulphate is present 
it is necessary to estimate this by itself, and the Na 2 S0 4 thus 
found subtracted from the total Na 2 S0 4 is B. As long as 
there is no sulphide present this can be done in the follow- 
ing manner. The liquor to be examined is heated in a 
flask and carbonic acid passed through till all the air is ex„ 
pelled. Then hydrochloric acid is added in excess, and the 
liquid boiled down in a C0 2 atmosphere to one fourth of its 
volume. After filtering it is precipitated with barium 
chloride as usual. 
