27S 
VALUATION OP BLEACHING POWDER, 
oxidize 1728 parts of crystallized protosulphate of iron (or 
10 grains of chlorine can peroxidize 78.1 grains of the crys- 
tallized protosulphate.) Now the process consists in dis- 
covering how much of the specimen of the chloride of lime 
is requisite to peroxidize 78.1 grains of the protosulphate? 
which quantity of the chloride must contain 10 grains of 
chlorine. 
".In the first place, 78 grains of the pure protosulphate 
(clean crystals of the salt dried by strong pressure between 
folds of cloth) are dissolved in about two ounces of water, 
and the solution is acidulated by a few drops of hydro- 
chloric or sulphuric acid. Fifty grains of the chloride of 
lime are weighed out, mixed well in a mortar with about 
two ounces of tepid water, and the mixture poured into an 
alkalimeter. The measure is filled up to 0, with the wash- 
ings of the mortar, and the liquids are well mixed by agita- 
tion, the mouth of the alkalimeter being closed by the palm 
of the hand. This solution of chloride of lime is then 
gradually added to the solution of 78 grains of protosulphate 
of iron, until the latter is completely peroxidized, which 
is discovered by means of the red prussiate of potash. 
This salt gives a precipitate of Prussian blue with a 
salt of the protoxide of iron only, and not with a salt 
of the peroxide ; so long then as it produces a blue 
precipitate, protoxide of iron still exists in solution, and 
more chloride of lime must be added. In applying red 
prussiate as the test, it is convenient to have a plate spotted 
over with small drops of its solution, which are touched 
with a drop of the liquid to be tested, taken out on the 
point of a glass stirrer, stopping short exactly at that point 
at which the red prussiate of potash ceases to afford Prus- 
sian blue. 
" The number of measures poured from the alkalimeter is 
carefully observed. The richer in chlorine the specimen 
of chloride of lime is, the less, of course, is required. As 
this amount, whatever it may be, but which, for example. 
