The Helpless Helper (1927)

Al's father, Professor Rockenrye has discovered a gasoline substitute. He can drop it on a toy train or wind up toy, and the train will start running and the toy will start moving. Al's girl Rose is at his house and opens the door when Al's rival arrives. The big lug is there to whisk her away and marry her. Stupid Al gives the rival a drink of the formula, causing the rival to spit fire. Al then spills all of the remaining formula, ruining the Professor's hope of fame and fortune.