Once More: "The Efficiency of
Acid at Low Temperatures"
by R. Irmscher
German Society for Pest
Control, Frankfurt am Main
Further to the recent publication in volume 8/9 of this journal *),
we shall report here on some additional experimental results of the
While at the time of the employment of thorough prussic acid
gassing in Poland in the winter of 1939/40 and later in France during
the winter of 1940/41 room temperatures up to -8 C had to be
overcome, the winter of 1941/42, with its abnormal demands in the
east, presented us with the question whether the usage of prussic
acid in the occasional low room temperatures to be found there could
technically be carried out at all.
It is known that liquid prussic acid freezes at a temperature of
-14° C. Upon superficial consideration, it could appear that in room
temperatures lower than -14° C, the evaporation of the prussic acid
absorbed in "Zyklon" is made so much more difficulty, i.e. delayed,
that within the given reaction times, the effective gas strength can
scarcely be reached. On the other hand, there is an absorbed
liquidity in finely porous material for the most varied of reasons,
not only in respect of its freezing point, but also its speed of
evaporation, which is different than in unabsorbed form. It was
therefore to be assumed, that even below the named temperature
limits, a sufficient evaporation of the absorbed prussic acid is
guaranteed, which in any event would first have to be proven through
Disposition of the experiments.
Suitable cold storage rooms were certainly available in which
temperatures could have reached as low as -18° C, but they were
unable to be freed up because they had been requisitioned from other
quarters for experiments with prussic acid. Thus, the observations had
to be carried out in an isolated trunk with a capacity of 6.6 cubic
meters, specifically designed for the task, in which the carrier
material of absorbed prussic acid (Zyklon) was scattered about in the
usual way in paper blotters. The trunk, lined with metal,
which was cooled in a large iced salt bath, demonstrated inside
sufficiently constant temperature levels. The cold period which began
in January of this year facilitated the completion of the experiments
in the described order.
In order to as much as possible offset sources of error that could
result from the leakage of the trunk or the adsorption of the prussic
acid into the material of the wall, the evaporation of prussic acid
was not measured by analysis of the air in the room, but through
weighing the remnants.
*) G. Peters and W. Rasch: The Efficiency of
Prussic Acid Evaporation at Low Temperatures, Journal for Hygienic
Zoology and Pest Control, Volume 8/9, 1941.