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2-pints of acid were added to each jar giving a strength of 1 in 760 to the diluted
solution. "With this quantity of acid the cowdung floors gave an acid reaction for
from 8 to 11 hours.
The amourt was then increased to 3 pints per jar giving a strength of about
1 in 500 in the diluted solution. This rendered the floors acid for periods varying
from 12 to 18 hours.
Four pints were then tried, giving a strength to the diluted solution of
1 in 380. This amount rendered the floors acid for at least 30 hours after dis-
infection. In the preparation of the solution therefore four pints was fixed upon
as the amount of acid necessary to be added to each jar.
The acid in the solution acts as a solvent for the Perchloride. It also acts as
a solvent of any albuminate of Mercury that may be formed allowing the Perchloride
therefore to penetrate through what would otherwise have been an impervious
covering protecting the germs. In addition to these two actions the Hydrochloric
acid has a distinct germicidal action of its own on the Plague Bacillus and is
itself a good disinfectant for this purpose. By rendering the floors acid tor periods
of 24 hours after disinfection this disinfectant action is continued after all the
Perchloride cf Mercury has been decomposed. In the first series of jars prepared,
Sodium Chloride was added to assist the solution of the Perchloride. The salt
supplied was covered with mud containing organic matter which actually decom-
posed the Perchloride, although the salt was washed as carefully as possible and
strained through several layers of cloth. The use of the Sodium Chloride was
dispensed with and it was not considered necessary to replace it with Ammonium
Chloride as the amount of Hydrochloric acid used was considered sufficient to
effect all that was required.
In a number of the jars a greyish muddy looking sediment was deposited
after the solution had been standing for 3 or 4 days. On testing the deposit it
was found to consist of Mercury in a very finely divided state with some organic
matter. Experiments were made to discover the source of this deposit and it was
found to be due to the organic matter contained in the water used for the pre-
paration of the disinfectant. When distilled water was used instead of water
from the main no sediment was deposited. It was also found that the sediment
was less when water from the main was used than when water from the cistern
was used. The water from these two sources was analysed and found to
contain a considerable amount of organic matter both in suspension and in
solution. By filtering the water through several layers of cloth the organic
matter in suspension was removed and the sediment deposited, when this
filtered water was used, was lessened in amount, but was not entirely removed.
This sediment was caused by the organic matter in solution. The form-
ation of this sediment could only be prevented by the use of distilled water, but as
distilled water in the large quantity required was not available, an additional quantity
of Perchloride of Mercury was added to each jar sufficient to cover any loss from this
cause.
On 16th May 1899 the sediment that had been deposited in 73 jars was collected,
dried and weighed. The total weight was four ounces giving an average of 24 grains
for each jar. The water that had been used in the preparation of these jars had not
been filtered.
On 31st May 1899 the sediment from 35 jars was collected and weighed.
It averaged 91/2 grains to each jar. The water used in the preparation of these jars
had been filtered.