Once More: "The Efficiency of
Prussic 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 same kind.

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 relevant experiments.

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.