VOL. 7, No. 4
METHYL OXALATE
827
METHYL OXALATE AND SUPERSATURATION
A solution of methyl oxalate in methanol is suggested as a combination with which to teach supersaturation, for the behavior of such a solution is very susceptible of control by varying the ratio of solute to solvent, and the temperature a t which one chooses to start crystallization. Many students think of solution only in terms of water, and the use of methanol here is an advantage in correcting this idea. The use of a thermometer in the solution before crystallization is induced by seeding or agitation will give a qualitative idea of what is meant by latent heat of solution. A solution made by warming methyl oxalate with methanol in the ratio of fifty grams of the former to 100 ml. of the latter is convenient. Of course methyl oxalate is relatively expensive, but not in terms of student results. The phenomenon of supersaturation is a hard concept for many students to grasp, partly due Lo the inherent difficulty of the idea, and partly due to the fact that the student does not alwayg have an opportunity to demonstrate the phenomenon to himself in the laboratory, and when he does, he finds that the suggested materials do not work out well in the hands of inexperienced operators. Both of these latter difficulties may be remedied by allowing each student to work with a solution of methyl oxalate, which always "works," and this combination, in conjunction with a thermometer as suggested, should readily give the student the idea that a supersaturated solution is really an unstable solution, and therefore not a t all a t variance with the definition of a saturated solution which specifies a state of equilibrium with undissolved material. Methyl oxalate is also a very convenient substance with which to demonstrate sublimation, supercooling, and metastability.
Abietic Acid Crystals Described. A four-color photomicrograph of abietic acid crystals grown in rosin is a feature of a 51-pa& booklet just issued by the Hercules Powder Company, Wilmington, Delaware. According to this well-illustrated booklet abietic acid is a cheap organic wid. It is one of a number of terpene chemicals and organic compounds discussed. The booklet may be had without cost by writing to the company.-The Catalyst
