53
These results show that the actual amount of Perchloride decomposed in each jar
is very small. The grey deposit consisted of finely divided Mercury ond 91/2 grains
of Mercury correspond to 12'87 grains of Perchloride. So by using filtered water
from the main the actual loss of Perchloride of Mercury in each jar averaged 12*87
grains out of 21/2 Ibs.
To counter-balance this loss an extra half ounce of Perchloride over and above
the 21/2 Ibs. is added to each jar.
Every week samples of the prepared solutions in stock were analysed. Until
the extra 1/2 ounce of Perchloride was added to each jar, the solution was often found
to contain a small fraction less than the full 10 per cent. This loss was in part due
to the decomposition of the Perchloride by the organic- matter in the water, and
partly to the alteration in the composition of the Perchloride which always takes place
to a small extent when a solution of the salt is kept fop any length of time. Some
experiments made to ascertain the loss from this cause gave the following results :—
A solution when freshly prepared was found to contain on analysis.,10 parts in 100.
After the same solution had been kept for four weeks it contained..9'982 do.
After eight
do.
..9'9 54 do.
i.e., after four weeks there was a loss of 31'5 grains of Perchloride of Mercury and
after eight weeks 80*5 grains.
As stated above an extra half ounce, i.e., 218.75 grains, is now added to each jars.
This is sufficient to cover the loss from keeping and the loss due to the organic
matter in the water and at the same time to leave a margin for any further loss.
Analysis made after the addition of this extra 1/2 ounce showed that the solution
always contained the full 10 per cent, of Perchloride of Mercury.
Several analyses were made of the diluted solutions taken from the buckets
of the solution actually being used for disinfection. The samples varied in strength
from 1 in 700 to 1 in 750. This increase of strength over the theoretical 1 in
760 showed that a little more than 5 ounces of the 10 per cent, solution was
being added to each bucket. The cups used for measuring out the strong solution
hold, when quite full, 6 ounces. This accounts for the excess of the strong solution
added.
In the preparation of the disinfectant care is taken that no apparatus or
materials are used that can in any way react on the Perchloride. The Perchloride
is kept in paper packets, it is powdered in a China mortar with a China pestle.
The acid is syphoned from the acid jars with a glass syphon, and glass or
China jugs only are used for measuring the acid and for transferring it to the
jars.
The cups supplied to the District Officers were at first enamelled iron cups.
They had no effect on the Perchloride solution at first, but the enamel was soon eaten
away and the iron exposed, so these cups were replaced by similar cups made
of thick glass.
No change was made in the orders regarding disinfection, but
towards the close of the year when the epidemic was declining it was
felt to be desirable to emphasize the necessity of uniformity and thorough-
ness in disinfection ; and on receipt of a report from Dr. Cayley, detailed
instructions were drawn up in consultation with him for the guidance of
all District Officers and forwarded to them together with his report.