2S2 
VALUATION OF BLEACHING POWDER. 
which is nearly requisite for the operation, and it is only 
then that the drop of blue sulphate of indigo is added. The 
number of measures employed is carefully observed, The 
richer in chlorine the specimen of chloride of lime proves, 
the less of course is required. To know the per centage 
which the number found indicates, the following method is 
adopted :— 
Suppose that twenty-five divisions have been employed, 
which indicate 5.1 of chlorine, it must be calculated how 
many times the number of divisions employed will go in 
100, namely, four times; then by multiplying 5.1 by 4, 
the result is 20.4 grains of chlorine, per cent. Should 20 
divisions be used, 100-;~20 gives 5; then 5.1 by 5 indicates 
25.5 grains of chlorine per cent., and so on for any other 
number found. 
In addition to the advantage of determining with ease 
the exact moment when the operation is at an end, this 
method affords, after a little practice, a very rapid mode of 
ascertaining the value of a bleaching liquor, and of being 
able to prepare a large bulk of standard liquor, which, by 
its non-deterioration, can be employed with safety for a long 
period, for by taking one thousand grains of it the value of 
a bleaching liquor can be determined in a short space of 
time. 
M. Gay Lussac also proposed the employment for stan- 
dard liquors of the yellow prussiate of potash, and the 
nitrate of mercury, transformed by a little chloride of sodium 
into protochloride ; but standards made with those sub- 
stances are in time susceptible of undergoing changes, which 
might lead to errors, besides, like the protosulphate of iron, 
they do not present a rapid indication of the moment when 
the operation is completed, — Pharm. Jour. 
