46 The Substitution of an Alkaline Base in Chlorimetry. 
from time to time by the usual methods, so much more satisfac- 
tory results were obtained than in testing bleaching powder, that 
I made a number of investigations to determine whether correct 
and expeditious results could be secured by converting the latter 
into the former. The result was that, at least as accurate 
determinations of the amount of available chlorine in the several 
samples were obtained by this means as by using the milky 
solution. 
As an excess of alkali is no inconvenience in testing, and 
thereby the liquid settles more readily and is more easily filtered, 
the usual mode of procedure is to dissolve 240 grammes of soda 
crystals (Na,CO,+10aq.) in one litre of water. This amount 
of alkali will be found sufficient for the strongest samples. One 
litre of this alkaline solution will test ten samples of bleaching 
powder where 10 grammes are operated on, and twenty samples 
where 5 grammes are taken. I generally weigh out 5 grammes 
of the sample of bleaching powder, than take 50 C.C. of the above 
alkaline solution, a little of which I add to the powder ina 
mortar, and triturate till there results a pasty mass; next the 
mortar is nearly filled with the alkaline solution, and the contents 
of the mortar rubbed up again with the pestle and transferred to 
a beaker. The remaining part of the alkaline solution is used 
for washing out the mortar into the beaker: water may be 
used to complete the washing if there be not enough of the 
alkaline solution. 
The contents of the beaker are allowed to settle a few minutes, 
and the quickness with which they do so, isa measure of the 
good quality of the lime used in the manufacture of the bleaching 
powder. Bleachers much prefer the lime bleaching liquors 
(solution of bleaching powder,) and alkaline bleaching liquors 
(the liquid I am now describing) which settle quickly. The 
supernatant liquid is then passed through a filter, and the 
precipitated carbonate of lime stirred up with some water and 
then thrown on the filter, the first portion of this filtrate should 
be received in a separate vessel as some of the fine precipitate is 
liable to pass through, but soon cease to do so, when these por- 
tions can be filtered over again. The beaker and filter is then 
washed ; and the washings are known to be complete when they 
no longer give a precipitate with nitrate of silver or discharge 
