Goddard realises after three years of unsuccessful tests that the cartridge rocket concept is too complex and that a new approach is needed. Smokeless powder solid fuels were too unstable for rocket use. Therefore Goddard turned to liquid oxygen and gasoline as propellants. On this date he bought his first can of liquid oxygen from Linde Corporation in Worcester. He had to haggle for it; the liquid form was then only a by-product in the process of extracting gaseous oxygen from the atmosphere. Goddard was charged $ 10 per 2 gallon flask, the minimum Linde would sell to him. References: 377 .