The fixed carbon content of the coal is the carbon found in the material that is left after volatile materials are driven off. This differs from the ultimate carbon content of the coal because some carbon is lost in hydrocarbons with the volatiles. Fixed carbon is used as an estimate of the amount of coke that will be yielded from a sample of coal. Fixed carbon is determined by removing the mass of volatiles determined by the volatility test, above, from the original mass of the coal sample. It is used as %C in computation for calorific value. Fixed carbon ignition temperature is approximately 750 to 900ºF.