Federal officials went to some lengths to extol the virtues of Zyklon. “The past 20 years has seen both a tremendous increase in the use of fumigation for the destruction of vermin on ships and great improvements in fumigation methods,” a publicly released Public Health Service report of July 24, 1931, announced. “In both cases the advances are due to the introduction of hydrocyanic acid as a fumigant. Leaving the cumbersome, laborious, and time-consuming sulphur fumigation, we have passed through the method of generating HCN, with its still cumbersome apparatus and paraphernalia, through the period of liquid HCN, complicated by the difficulty of transporting so dangerous a material, and have arrived at the exceedingly simple procedure of knocking a hole in a can of Zyklon, pouring the contents down the hold, and throwing the can overboard.”11 Zyklon could simply be dumped through an opening into an enclosed space to effectively kill the vermin inside.
Another PHS report of the period noted:
For some time the American Cyanamid Co., of New York, has been endeavoring to develop a practical means of measuring small doses of “solid type” cyanide products for use in fumigating super-structure compartments on ships. The New York Quarantine Station has cooperated with representatives of this company by suggesting possible lines of development and by testing containers and material. The selection of a porous material seems undoubtedly influenced by the growing popularity of Zyklon, and with the HCN discoids the difficulty of measuring small doses required for use in fumigating small compartments has apparently been overcome. This has been done by developing a product, representing HCN in a solid form, in units, each unit carrying a definite and relatively small amount of fumigant.12
Although the PHS reports referred only to bugs, researchers realized that the findings had other implications—particularly ramifications for human beings who might be exposed to the poison. Scientists had become increasingly aware that cyanide was actually more effective on warm-blooded animals such as human beings than on insects, because vertebrates carry oxygen in their blood via hemoglobin, whereas insects do not. In humans, cyanide was also absorbed through the lungs, gastrointestinal tract, skin, and especially the mucous membranes and the eyes. Unprotected exposure and breathing of the hydrogen cyanide gas in an enclosed space therefore appeared especially deadly to people. However, gathering proof of that fact would have to be left to prison authorities.
The government reports about the killing power of Zyklon and other forms of hydrocyanic acid were widely distributed, with some copies going to its officers who were posted in Germany and other foreign countries, and others going to foreign and domestic company executives. PHS officials and their foreign counterparts also traveled back and forth between Europe and the United States, and the military and commercial implications of the tests guaranteed that there was no doubt that German chemical executives knew about the American tests involving Zyklon and other poisons. Every public health official in charge of American prison operations also received a copy of the reports.
Zyklon contained a lacrimatory warning agent of chloropicrin or cyanogen chloride, which acted as an irritant to cause tears and other discomfort to prevent unwanted death from the lethal gas. This use of chloropicrin as a warning agent was invented by Hans Lehrecke of Frankfurt am Main in 1925 and assigned to Roessler & Hasslacher of New York by U.S. Patent 1,786,623 on December 30, 1930. But such warning agents would be considered counterproductive for executions, both because the irritants caused unwanted discomfort and suffering and because they did not lend themselves as neatly to the execution ritual. One of the chief selling points of cyanide gas as an execution tool was that it was supposed to kill quickly, without warning or pain. Its planners did not want witnesses to report otherwise. Hence Zyklon did not appear well suited as an execution gas. (In Nazi Germany, DEGESCH would later manufacture Zyklon without the troublesome warning agent, thereby overcoming this obstacle and making the deadly agent less detectible to humans.)
Fritz Haber had established a rule in inhalation toxicology that stated: C ÷ T = constant, meaning that identical products of concentration of an agent in air (C) and duration of exposure (T)—the C ÷ T product—will yield an identical biological response. Based on his research under Haber during World War I, his assistant Ferdinand Flury determined that the value of C ÷ T for hydrogen cyanide depended upon its concentration. As an outgrowth of Haber’s law, Flury in 1921 had published the equation:
with g denoting the amount of poison taken up, G the body weight of the experimental animal, and Z the number where a certain effect (for example, death) occurred. As far as the inhaled poison was concerned, wrote Flury, “It is possible to define g as a product of three factors: the number of milligrams of the poison present in one cubic meter of inspired air (C), the number of minutes (T) during which air with the concentration C of the poison is inhaled, and finally A, expressed in cubic meters, the volume inhaled by the animal per minute.”
According to Flury’s experiments, it was possible to use the equations he and Haber had developed to compare with reasonable accuracy the effects of different toxic inhalants. Based on their varying concentrations and breathing times, not all toxic war gases had constant effects, with the exception of hydrocyanic acid. But HCN did, and this made it particularly suitable for executions as far as the American prison authorities were concerned.
Flury described an experiment he conducted involving hydrocyanic acid. As explained by a scientist writing in 1999:
Originally, paper bags filled with sodium or potassium cyanide were placed beside vats filled with dilute sulfuric acid. A technician then emptied the contents of the bags into the sulfuric acid while working his way towards the exit of the room. The procedure was obviously hazardous, and so better methods had to be developed. In such an improved process, hydrocyanic acid and a strong irritant, for example xylilbromide, were bound to an inert carrier (infusorian earth) and kept within tin cans. When the cans were opened and the material dispersed onto the floor of a room, both the cyanide and the irritant evaporated, the irritant serving as a warning sign for the presence of the lethal gas. The process was called the “Zyklon system.” It was later commercialized and several companies were licensed to manufacture it.13
Thus it was evident in the chemical field that although Zyklon may not have been ideal for use as an execution gas in American prisons due to its irritating warning agent, other forms of hydrocyanic acid could be better suited. Dipped by string into a mixture of sulfuric acid and water, as part of the established “bucket” or “pot” method, a gauze-wrapped pouch of sodium cyanide or potassium cyanide could produce the lethal agent with manageable and predictable results.
So far, no records have turned up to document why prison authorities opted against the more commonly available sodium cyanide. However, given the widespread use of that material in fumigation, the companies involved may not have wanted to have their product identified in the public mind as being highly lethal to humans. Instead, the decision makers may have preferred to utilize a form of cyanide that was already known to be lethal; indeed, the newspapers had long reported it had figured in many suicides and murders. And besides, potassium cyanide was not presently manufactured in the United States.