2. the distribution and penetration of the gas were not somewhat reduced.

It was even to be accepted that gas losses through adsorption were especially elevated and that in cold rooms often a significantly greater decrease in humidity on the walls occurred than in warm rooms.

In the laboratory on the other hand, the question to be answered was the extent to which the capacity for resistance of bed bugs in all forms of development to prussic acid is increased at low temperatures, and whether at low temperatures required higher grams per hour consumption could be detected through the desired prussic acid concentrations at practical fumigations.

The experiments, carried out in both directions yielded the unequivocal corroboration of the opinion grounded in practical observation over many years, that the efficiency of prussic acid and the suitability of the Zyklon procedure encompasses a temperature range that with certainty reaches at least 10° below zero.

Finally a question had been answered that first arose in 1925 after the evacuation of a part of the Reich territory that had been occupied by the Allies during an especially harsh winter. To be sure, at that time they still did not have the insight into the dependency of the poisoning efficacy of gases on temperature and contented themselves with the statement that after fumigation, the obstacles could not be overcome due to imperfect efficacy. However, in many cases, it involved barracks that had been empty for weeks; the internal temperature of the buildings at the time of the fumigation was therefore generally not much higher than the external temperature, which on many days reached -22°.

There was at that time not yet the necessity for and also no possibility of a thorough examination because there seemed to be only one special action involved whereas the normal fumigation activity had its high point in summer and sank to a minimum in the cold times of the year. Only with mill fumigation and combating other storeroom pests was there already to be observed a significant difference in the number of fumigations in warm and cold times of the year, because even some customers chose the winter as the most favorable time of year for their purposes. However, even in these cases, winter fumigation with zyklon prussic acid had for years brought no disappointments.

Examination of practical fumigation tasks.

After numerous fumigation objects had already resulted in certainty from practical observation about the 100 percent mortification success even at room temperatures to -10°C, the above questions were thoroughly tested in specially designed barracks buildings. Some of the test results are summarized below:

Speed of prussic acid from Zyklon.

1. Barracks building A, area 39,183 cubic meters
Zyklon consumption 396.8 kg CN = 10 g/cbm
Gas applied 17 January 1941 morning 11:30