By way of example we may take a mixture of mineralised methylated spirit and benzene - containing, say, 20 per cent. of the latter, by weight. Then 1 gram of the mixture contains 08 gram of the mineralised methylated spirit and 0 2 gram of benzene. Taking the higher calorific values already given for the constituents, we have: -

This is the "higher" or gross value, taking the benzene as pure benzene. In practice, commercial "benzol" would be used, containing more or less toluene, xylene, etc., and giving a somewhat greater calorific value than pure benzene. The "lower" calorific value of the mixture, calculated on the principles already explained, will be found to be 6,4748 gram-calories = 11,6546 B.Th.U.

In general, it is better to have calorific values as determined by careful experiment rather than the calculated theoretical values, as the latter involve certain assumptions which may affect the results to some extent. The experimental values obtained for alcohol and methylated spirit by various observers show some differences, as might be expected, since the determination presents several difficulties. Lewes gives the following: -

Brame gives the following as mean values from all the trustworthy determinations available. The net values have been calculated from the gross values on the assumption that in the latter the water formed was condensed to a final temperature of 15.5°.

Calorific values, experimental.

Limits of inflammability (Thornton).*

* Phil. Mag., 1917, 33, 190.196.