In August 1941, Höss' deputy, Karl Fritzsch, tested out an idea. At Auschwitz, clothes infected with lice were treated with crystals of prussic acid (hydrogen cyanide). The crystals' brand name was Zyklon-B. They were made to order by the IG Farben chemicals company. Once their container was opened, the Zyklon-B crystals in the air released a deadly cyanide gas. Fritzch thought this gas could be used to kill prisoners. To try out the effects, he locked some Soviet prisoners of war in the basement of a bunker and gassed them. They died.