The "Continuously Sensitive Diffusion Cloud Chamber," as it was originally called, was developed at UC Berkeley in 1938. They tested many different substances to vaporize, and surprisingly the only one that worked was evaporated 95% ethanol or methanol. In the original design, they replaced the air in the cloud chamber with a carbon dioxide atmosphere, but this is not necessary today. One of the limitations they ran into was the limited photography techniques they had back in the late 1930's, which means you can record this experiment much better than the original researchers ever could!

To read the original journal publication, check out the PDF here.