How is the rate of heating adjusted when using a sand bath as a heat source?

When the heat source used is a sand bath the rate of heating will be slow this is due to fact that the specific heat of sand is smaller compared to water. sand bath is desired when the temperature is above 250 C which an oil bath is not already capable. in a sand bath the heating slow and also cooling is slow.

therefore, the efficiency is:

It equals just about 6,300 km per hour each day an week