- NOTES ON SCIENTIFIC RESEARCH. ; 97 
" erystallo-microscope?) has proven that numerous bodies may be obtained in two or 
_ more different modifications when the experimental conditions are altered. Principally, 
“the temperature is decisive for the change of one form into another one. This takes 
place also with menthol which, according to F. E. Wright’), crystallizes in at least four 
“different forms discernible as @-, @-, y- and 0-form. Of these, only one, the «-form of 
_ ordinary menthol, is stable in the temperature range between 0° and its melting point 42.5°. 
The other three forms are monotropic and show lower melting points: 6-form, m.p.35.5°; 
% y-form, m. p. 33.5°; 0-form, m. p. 31.5°. The unstable forms, on standing, pass over into 
the stable modification, the 0-form, wd@ the @-form. 
% It was difficult to measure the angles of ordinary (¢-form) menthol crystals; anyhow, 
it could be stated with certainty that the crystals belong to the hexagonal system, as 
had been demonstrated -years ago by Des Cloiseaux’). Melted «-menthol, for which 
_ Wright found np:;0 about 1.458, was lzvorotatory, the crystals, however, showed a 
_ dextrorotation of the five-fold strength. 
____ All the forms of menthol show the tendency to form radial ephenmliees when cry- 
- stallizing. 
. With use of the oe ootitt microscope, the transformation of the separate modi- 
7 ations into the stable «-form could be observed easily, it was even possible to 
easure the rapidity of the transformation of the y-form into the «-isomeride. 
The occurrence of the separate modifications is principally dependent on the tem- 
_ perature down to which the melted menthol cooled. Between 42 and 38° principally 
_ a-menthol crystallizes out, between 30 and 18° the y-form, and between 18 and 3° the 
ee sor, and between 5 and 12° the 0-form. 
ee ma | 
= Some years ago, C. Tubandt demonstrated that the inversion of menthone is a species 
reversible reactions of the first order most admirably fit for kineto-chemical investi- 
gation. Reciprocal reactions may be measured in the same temperature range with 
equal exactness and readiness, so that in this case the theory of a monomolecular 
_ reciprocal reaction could be confirmed with the necessary degree of certainty by ex- 
_ perimenting from both sides of the equation. Recently, W. A. Gruse and S.F. Acree*) | 
_ have been working on the inversion of menthone and published their results under the 
title, “The reactions of both the ions and the molecules of acids, bases, and salts; the 
"inversion of menthone by sodium, potassium, and lithium ethylates”. They studied the 
z inversion of /-menthone by the aforesaid ethylates in solutions of absolute alcohol at 
a>°, working in very low concentrations in order to avoid abnormal salt or solvent 
effects. When discussing Tubandt’s work, Acree’) had expected that, in case the 
_ ethylate ion be the active principle for the inversion, the constant for this reaction 
would have to be the same one, independant on which of the three ety lates the cal- 
culation is based. 
2s _ The measurements were performed with dilutions of 1:32 up, toy1! a12: at. 25°: 
= with Acree’s expectation, the identical activation constant of the ethylate ion 
1) For studying the formation and transformation of crystals, especially the liquid crystals, use is made 
Lehmann’s crystallization microscope, which consists in the main of an ordinary microscope, but with a 
to heat the test-object and, on the other hand, a contrivance to blow cold air on the same, in 
er to keep the temperature somewhat constant. Equally, the test-object may be cooled by means of a 
- current of water. — 7) Journ. Amer. chem. Soc. 89 (1917), 1515. — %) Compt. rend. 70 (1870), 1211. — 
4 Journ. Amer. chem. Soc. 39 (1917), 376. — 5) Amer. chem. Journ. 48 (1912), 359; Chem.. Zentralbl. 1912, 
a6 7) 
