A compound consists of 81.7 percent by mass carbon and 18.3 percent by mass hydrogen What is the empirical formula of this compound?

Alidded glass container is filled with a colored gas. after a period of time, it is observed that the gas is uniformly spread throughout the box and that the movement has slowed considerably. next, a warm iron plate is carefully placed under the box. why is there resumed movement of the gas in the container?