These cards came in small tins which included small mint or violet gum. I'm not sure what violet gum is, but I think it refers to the color of the small round gum pieces. I assume the mint chips were green while the violet chips were purple.
In my opinion, Rube Waddell was one of the premier pitchers of the late 1800s and early 1900s. It was well documented in the Ken Burns' "Baseball" documentary that Waddell was an odd fellow. He is said to have left the dugout, on occasion, to chase a firetrucks as they passed along the ballpark.
Whether his actions were a reaction to alcohol, or whether he was just a little off, or whether he had some sort of mental illness, there's no arguing Waddell's numbers. He ranks tenth all-time in career ERA with a 2.16. In 1946 he was elected into the National Baseball Hall of Fame.