AVAILABLE CHLORINE 329 
and beat until all of the arsenious acid is in solution. Cool and make 
up to 1 liter with distilled water. 
2. Iodized starch paper. 
Dip pieces of filter or other bibulous paper into a starch solution 
containing a very small amount of potassium iodide. Moisten when 
using. 
Procedure. ‘Transfer 50 c.c. of the bleach solution (either that pre- 
pared from the powder or that taken from the orifice box) to an Erlen- 
meyer flask. Add very slowly the N/10 arsenious acid solution until a 
drop of the solution causes no dark coloration on the moist iodized 
starch paper. The number of cubic centimeters of arsenious acid 
solution used is equivalent to the percentage of available chlorine in the 
bleach. — 
1 c.c. N/10 arsenious acid = .003545 gram cl. 
The computation to determine how much available chlorine may 
be made as follows: Take 50 c.c. of bleach solution from the orifice box 
and titrate with N/10 NasSeO3. One c.c. of this is equivalent to 
0.003545 gm. chlorine. If the 50 c.c. of bleach solution requires 30 c.c. 
of N/10 NagSe2Os3 then 30 0.003545 & 20 = 2.127 gms. chlorine per liter. 
One liter=1000 gms., then the solution contains .2127 per cent 
available chlorine. A cubic foot of the solution weighs about 28,320 
gms. In this case then 1 cu. ft. of the solution will contain 59.094 
gms. of available chlorine. 
Examination of Water for Available Chlorine. The Committee on 
the Analysis of Water and Sewage of the American Public Health Asso- 
ciation recommended the following procedure. This has not been 
accepted by the Canadian Public Health Association. They have 
recommended that it be eliminated from standard methods. (Amer. 
Jour. Pub. Health 8. (1918) 320.) 
In waters that have been treated with calcium hypochlorite or liquid chlorine 
it is frequently advisable to ascertain the presence or absence of available 
chlorine. As the reagents which have been proposed for its detection are not 
specific for chlorine but give similar or identical reactions with oxidizing agents 
or reducible substances, care must be exercised in interpreting the results of such 
tests; nitrites and ferric salts are of common occurrence, and chlorates also may 
lead to misinterpretation in waters treated with calctum hypochlorite. 
Reagents 1. Tolidin solution. One gram of o-tolidin, purified by being 
recrystallized from aclohol, is dissolved in 1 liter of 10 per cent hydrochloric 
acid. 
2. Copper sulphate solution. Dissolve 1.5 gms. of copper sulphate and 1 c.e. 
of concentrated sulphuric acid in distilled water and dilute the solution to 200 c.c. 
