Hoss apparently was not aware, nor was Eichmann, that the suitable gas was already available. It was called Zyklon B, a commercial form of hydrocyanic acid, which became active on contact with air. It was manufactured by a firm called Degesch, which was largely owned by I.G. Farben, and it had been brought to Auschwitz in the summer of 1941 as a vermin-killer and disinfectant.
Friedrich, p. 17.
"The door would now be quickly screwed up and the gas discharged by the waiting disinfectors through vents in the ceilings of the gas chambers, down a shaft that led to the floor. This insured the rapid distribution of the gas. It could be observed through the peephole in the door that those who were standing nearest to the induction vents were killed at once. It can be said that about one-third died straightaway. The remainder staggered about and began to scream and struggle for air. The screaming, however, soon changed to the death rattle and in a few minutes all lay still...The door was opened half an hour after the induction of the gas, and the ventilation switched on...The special detachment now set about removing the gold teeth and cutting the hair from the women. After this, the bodies were taken up by elevator and laid in front of the ovens, which had meanwhile been stoked up. Depending on the size of the bodies, up to three corpses could be put into one oven at the same time. The time required for cremation...took twenty minutes."
Friedrich, p. 32.