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"4th. The manganate and permanganate of potass.
" These constitute the active principles in Condy's disinfecting fluid, and
form an admirable means for destroying impure gases. They, however,
with others, have hitherto rank'-d only amongst, the strictly local disinfectants,
and from their non-diffusible nature could not be satisfactorily
applied to the pases pervading the atmosphere of large sewers.
"The permanganate of potass is asubstance havingthe peculiar property
of freely and easily parting with a portion of its combined oxygen to any
oxydizable organic substance. The potassium, like other metallic bises,
decomposes the sulphuretted hydrogen and sulphide of ammonium, whilst
the oxygen set free, unites with or burns as it were the remaining
noxious gases arising from putrescent organic matter.
" The mode by which 1 think they can be made available is by saturating
very coarsely-powdered charcoal with a rather strong solution,
and securing the passage of the sewer air through the material by means
of the series of trays or metal tubes before alluded to.
" The above chemical agents are none of them new, but are all well
tried servants in sanitary science; nevertheless, though they have been
used as disinfectants in the ordinary manner, none have as yet been
applied to the decomposition of sewer gases in an apparatus so fraught
with advantages as that suggested by Mr. Bean and myself. The
manner in which they have been generally used has been by merely
suspending flannels, &c., saturated with the various solutions, either in
the sewers or ventilating shafts, necessarily allowing a very large proportion
of the gases to escape, without contact with the disinfectant, a
circumstance which it is believed will be avoided by the use of the proposed
apparatus.
" A very important advantage in it is,'that the action will be entirely on
the gaseous matters. No extraneous substance will be added to the
contents of the sewers ; at any rate there would be nothing to interfere
with the utilization of the sewage, should such be found practicable and
desirable.
" The large experience and many favourable opportunities for investigation
enjoyed by Dr. Letheby. have enabled him to give to the world a
valuable store of practical deductions, and it would be presumptuous in
me now to go further into details on this subject. If the apparatus now
under your notice fails to accomplish all that can be desired, I am quite
certain that it will be instrumental in diminishing to a most sensible
extent the offensiveness of the ventilating shafts; that its cost will not
be excessive, and that the expense of maintaining it in action will be
trifling compared with the advantages obtained. The charcoal may be
washed and used almost ad infinitum. The oxide of iron may be revived
by exposure to the air, and us^d for a very lengthened period, and even
it Condy's patent solution were u^ed, it may be purchased according to
Dr. Letheby at a cost of about Is. per gallon. The apparatus should be
under the supervision of the Officer of Health or Surveye>r. but the
replenishing and removal of tl e material, when ordered, might be accomplished
by any shrewd workimm belonging to your ordinary staff.
" I do not apprehend there will be any necessity for a very frequent
change of the disinfectant, except during the existence of an epidemic, or
in very hot weather ; and I tbink a series of chemical test-papers can be
so arianged and applied, as to indicate when such change is necessary,
without trusting to the sense of smell.
" In e< nelusioo, Gentleman, allow me to repeat my belief that whether
the means thus so very imperfectly presented to your notice, sufficiently