Förintelsematematik

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.

The previously noted quantities of Zyklon for the various experiments were cooled to the foreseen temperature for the experiment. As absorption material paper disks were used in one case, in another case erco cubes (highly porous gypsum material), that is the two most often used carrier materials in the implementation of prussic acid gassing. In order to get an overview of the entire temperature range, the experiments were carried out in the same order at -18° C, -6° C, 0° C, and +15° C.

In any event the calculation of relationships could not be made using this procedure in cases in which the humidity in the room is high thereby depositing upon the evaporating surfaces water or snow (depending upon the temperature) which significantly diminish the rate of evaporation.

Results of the experiments.

The resulting values are set out in the following tables and the diagrams further below:



Table 1
Release of prussic acid from absorption in cardboard disks.


Duration -18 to -19° C -6° C 0° C +15° C
after 1 hour 32.5% 50.0% 62.6% 77.0%
" 2 " 45.0% 84.1% 90.7% 96.8%
" 3 " 60.5% 95.7% 98.0% 100.0%
" 4 " 72.0% 100.0% 100.0% -
" 5 " 84.0% - - -



Table 2
Release of prussic acid from absorption in erco cubes.


Duration -18 to -19 C -6 C 0 C +15 C
after 1 hour 31.5% 45.0% 55.0% 57.0%
" 2 " 45.5% 73.0% 85.7% 96.4%
" 3 " 58.5% 95.2% 99.0% 100.0%
" 4 " 72.0% 100.0% 100.0% -
" 5 " 82.0% - - -





Illustration 1 Diagram.
*) From J.H Perry and F. Porter. Journal of American Chemical Society 48, 299; 1926.

37

The relatively favorable evaporation speed even below the freezing point temperature is straight away explained by the vapour pressure prevailing at those temperatures, that at -28° C still amounts to around 50 mm. The diagram in illustration 2 indicates the dependency of the vapour pressure on the prussic acid temperature above and beneath its freezing point.





Illustration 2. Diagram.
**) From G. Bredig and L. Teichmann. Z.S. Elch 31, 449; 1925.



Summary.

As a result of the experiments it can be considered to have been proven that absorbed prussic acid both at significantly low temperatures and above its freezing point, can be brought to evaporation sufficiently quickly that the requited gas strength for delousing activities can be achieved within the usual time-frames. Admittedly, the release of the gas is significantly slowed down at low temperatures; but even at -20 C more than half the prussic acid is released within 3 hours. The remaining evaporation occurs at this temperature approximately within 7-8 hours, unless it is delayed by excess dampness or formation of snow on the evaporation surface. With the corresponding slowing down of the reaction time a successful thorough gassing with prussic acid in these circumstances is technically not hindered. The biological reaction of prussic acid at low temperatures has already been reported on.