Improvements in Disinfecting by Means of Formic Aldehyde.
Year: 1898

page_text: PROVISIONAL SPECIFICATION.
Improvements in Disinfecting by Means of Formic Aldehyde.
I, AUGUST ZIMMERMANN, of 9 & 10, St. Mary at Hill, in the City of London,
Merchant, do hereby declare the nature of this invention (which has been com-
municated to me from abroad by The Chemische Fabrik auf Actien vormals
E. Schering, of 170 and 171, Müllerstrasse, Berlin, in the Empire of Germany),
to be as follows:-
It has hitherto been considered impossible to efficiently disinfect a room by
the mere evaporation of a formic aldehyde solution (formalin) although this
method is naturally the simplest and cheapest. It is agreed that disinfection of a
large scale by heating the 40% formic aldehyde solution on the market is not
practicable because of the formation of polymeric formic aldehyde.
In order to utilize the formic aldehyde solution as a disinfectant, it has been
sought to counteract the separation of polymeric aldehyde by the addition of
suitable substances.
Several such processes of disinfection have been suggested which may be dis-
tinguished from each other by the nature of the substance added and the special
methods of carrying out the disinfection. In the process of Dr. Rosenberg
methyl alcohol serves as the means for preventing polymerisation, in Trillat's
process calcium chloride heated in an autoclave when mixed with 40% formic
aldehyde solution serves for this purpose, and in the Schlossmann-Walter process
glycerine is used for the like purpose, which together with formic aldehyde
solution is sprayed with steam.
My correspondents have now found that such additions are not required to
thoroughly and successfully disinfect by means of formic aldehyde solution.
This is attained in the most simple manner by evaporating a very dilute formic
aldehyde solution. Hitherto the 40% formic aldehyde solution on the market
has always been the starting point because the formic aldehyde is here in its
most concentrated state. It appears paradoxical to first dilute the formic aldehyde
solution for disinfecting purposes, this however is the most simple solution of
the problem.
By this method of proceeding there of course remains behind a certain quantity
of concentrated formic aldehyde solution which may separate upon further
evaporation. The novelty and originality of this process lies in the fact that
first polymeric formic aldehyde is formed only in quite trifling quantities and in
the fact that secondly with suitable dilution polymerisation can only take place
after the quantity of formic aldehyde necessary for disinfection has been evolved.
Under these circumstances when the desired effect is attained dilution of the
formic aldehyde solution may be suspended. A further effect of this process
consists in that a large quantity of moisture passes into the room to be disinfected,
whereby the disinfecting action of the formic aldehyde is considerably increased.
To disinfect a room of 100 cubic metres I proceed in the following manner: --
600 grammes of commercial 40%, formic aldehyde solution (equivalent to
240 grammes formic aldehyde) is diluted with about from 3 to 3 litres of water
and the diluted formic aldehyde solution is heated in a vessel either in the room

page_text: to be disinfected or outside the same, in which case the evolved vapours are
led into the room by means of a pipe. With such dilution, about 200 grammes
of formic aldehyde gas passes into the room in question before the concentration of
the remaining solution attains 40 or more per cent., that is to say, 2 grammes
of formic aldehyde per cubic metre, which is a sufficient quantity to kill the
germs of infection.
Preferably heating is now stopped, that is before therefor
any polymerisation takes place. Evaporation may however be carried further, in
which case the small remainder of polymerised formic aldehyde is wholly vola-
tilized. The main purpose is thus now attained, that is to say, the room to be
disinfected is filled with a sufficient quantity of formic aldehyde, which would
not be possible if undiluted formic aldehyde solution alone were heated without
the use of substances to counteract polymerisation.
For evaporating such dilute formic aldehyde solution, an evaporating vessel
having narrow outlet orifices or tuyeres is suitable, through which at the same
time a spraying is effected.
The apparatus described in the Specification of the Patent No. 26667 of 1896
may also be employed, by its use no polymerised formic aldehyde is formed
because the suction caused by passage of the gases of combustion into the
receptacle containing the dilute formic aldehyde solution causes the formic
aldehyde vapours to be carried quickly away, so that the solution never becomes
too highly concentrated.
This
The before described process of disinfection with dilute formic aldehyde
solution may be varied by gradually adding the diluent (usually water) to the
formic aldehyde solution whilst the evaporation or spraying is going on.
is done by the use of a drip apparatus or drop arrangement which can be regulated
in such a manner that the diluent flows into the formic aldehyde solution in
proportion as the latter becomes evaporated. Any suitable drop apparatus may be
used.
Such modification of the process has the advantage, that all formation of
polymeric formic aldehyde is prevented, because the original formic aldehyde
solution can not only not become concentrated, but in consequence of the addition
of water must become actually more dilute until at length all formic aldehyde
is driven off. The whole quantity of formic aldehyde is thus quantitively utilized
for disinfection, so that there is no need to use any excess of formic aldehyde
solution. By this arrangement if 2 grammes of formic aldehyde per cubic metre
of space be taken as the necessary quantity for the production of thorough
disinfection', then for a room of 100 cubic metres 500 gramimes of 40% formic
aldehyde solution will be required. The amount of water gradually added hereto
is reckoned preferably at about 3 litres.
Dated this 1st day of Novamban 1000
COMPLETE SPECIFICATION.
. Improvements in Disinfecting by Means of Formic Aldehyde.
I, AUGUST ZIMMERMANN, of 9 & 10, St. Mary at Hill, in the City of London,
Merchant, do hereby declare the nature of this invention (which has been com-
municated to me from abroad by The Chemische Fabrik auf Actien vormals
E. Schering, of 170 and 171, Müllerstrasse, Berlin, in the Empire of Germany),
and in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement:-
It has hitherto been considered impossible to efficiently disinfect a room by
the mere evaporation of a formic aldehyde solution although this method

page_text: is naturally the simplest and cheapest. It is agreed that disinfection on a
large scale by heating the 40% formic aldehyde solution on the market is not
practicable because of the formation of polymeric formic aldehyde.
In order to utilize the formic aldehyde solution as a disinfectant, it has been
sought to counteract the separation of polymeric aldehyde by the addition of
suitable substances.
Several such processes of disinfection have been suggested which may be dis-
tinguished from each other by the nature of the substance added and the special
methods of carrying out the disinfection. In the process of Dr. Rosenberg
methyl alcohol serves as the means for preventing polymerisation, in Trillat's
process calcium chloride heated in an autoclave when mixed with 40% formic
aldehyde solution serves for this purpose, and in the Schlossmann-Walter process
glycerine is used for the like purpose, which together with formic aldehyde
solution is sprayed with steam.
My correspondents have now found that such additions are not required to
thoroughly and successfully disinfect by means of formic aldehyde solution.
This is attained in the most simple manner by evaporating a very dilute formic
aldehyde solution. Hitherto the 40%, formic aldehyde solution on the market
has always been the starting point because the formic aldehyde is here in its
most concentrated state. It appears paradoxical to first dilute the formic aldehyde
solution for disinfecting purposes, this however is the most simple solution of
the problem.
Experiments have shown that from dilute formic aldehyde solution great
quantities of formic aldehyde, in a state suitable for the disinfection of a dwelling
may be evolved without polymerisation taking place and that the yield in formic
aldehyde is relatively the greater the more dilute the formic aldehyde solution
used. A further effect of this method of evolving formic aldehyde is that a great
quantity of moisture is produced in the space to be disinfected whereby the
disinfecting action of the formic aldehyde is considerably increased.
To disinfect a room of 100 cubic metres I proceed in the following manner:-
800 grammes of commercial 40% formic aldehyde solution (equivalent to
320 grammes formic aldehyde) is diluted with about 3200 cubic centimetres of
water and the diluted formic aldehyde solution is heated in a suitable vessel either
in the room to be disinfected or outside the same, in which case the evolved vapours
are led into the room by means of a pipe. With such dilution which corresponds
to about an 8% formic aldehyde solution there remains behind, after evolution
of sufficient quantities of formic aldehyde for disinfection, a 4 to 6% formic
aldehyde solution, that is to say, a more dilute solution than the solution started
with. The room is thereby filled with 25 to 3 grammes of formic aldehyde per
cubic centimetre, a quantity fully sufficient to kill the germs of infection. It
is preferable to cease heating before complete evaporation, this is however not
essential.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is: :―
The production of formic aldehyde in admixture with water vapour in a state
suitable for disinfecting purposes by heating a solution of formic aldehyde so
diluted with water that polymerisation does not take place.