at 163-167'0 is collected. The yield of this fraction varies in
different runs from 430 to 470 g. (13-15 per cent of the theoretical
amount), but very often will be as high as 500 g., and has reached,
in certain experiments, 600 g.

An alternative method for the purification of the crude material
has been employed by Clarke and Hartman, and yields a slightly
higher-grade product than the sodium method. It is as follows:

The combined distillates are treated with an equal volume of concentrated
sulfuric acid and the solution warmed on a water bath for an hour,
under a reflux condenser, with occasional shaking or, better, with
mechanical stirring. Upon cooling, mesitylene sulfonic acid crystallizes
and the unsulfonated material remains as an oil on the surface.
The mixture is filtered through flannel or a "filtrose" plate,
and the crystals are washed with 60-70 per cent sulfuric acid.
The oily layer is again warmed with sulfuric acid, as before.
The acid and oily filtrates from the two sulfuric acid treatments are steam
distilled, and the distillate combined with the next batch of material.
The crystals are mixed with 2 l. of 15 per cent hydrochloric
acid and heated under a reflux condenser for two to three hours.
The reaction mixture is now steam distilled, the mesitylene separated,
dried over calcium chloride and fractionated; the portion which boils
at 163-167'0 is collected.

2. Notes

The cooling of the reaction flask must be very efficient, a 10-15 cm.
blanket of a thorough mixture of ice and salt being used.
If this precaution is not employed, the time for the addition