(17 ) 
The change occurs less readily the greater the excess of d or / 
which is present and proceeds very slowly. At 75 °/, it could not 
be observed even at the ordinary temperature. 
The monosymmetric crystals change to a granular mass; when 
excess of d or / is present this is of course only partial. 
The transition temperature in this case could not be detected 
by means of the thermometer or of the dilatometer but only by 
means of the microscope and then only when the temperature was 
rising. With 50°, the change is complete at the maximum tempe- 
rature; with the other mixtures the change is gradual; the line 
FGH represents the temperatures at which the racemic compound 
in a given mixture has just disappeared. All points between the 
two branches represent conglomerates of the compound with mixed 
crystals. 
The course of the conversion of mixed-crystals into a compound, 
deduced by me on theoretical grounds, is therefore completely con- 
firmed by this first example. 
Chemistry. — „On the Enantiotropy of Tin”. By Dr. Ernst 
Conen and Dr. C. van Eyk (Communicated by Prof. H. W. 
Baktiurs RoozEBoom). 
(Read in the meeting of June 24th 1899). 
1. That pure tin falls into a grey powder when exposed to great 
cold is a phenomenon with which the tin traders of Russia espe- 
cially have been long familiar. The phenomenon is, in that country, 
so common that a special name has been given to the tin powder 
which may be translated as tin which may be scattered. 
The phenomenon has been very frequently referred to in scien- 
tifie literature; the first description of it is due to ERDMANN !) in 
1851. He is followed by Frrrscue ®), LEWALD *), RAMMELSBERG x) | 
Ouvemans °), Warz °), Perri’), SCHERTEL ®), RAMMELSBERG ®), 
1) Journ. f. pract. Chemie 52, 428 (1851). 
2) B. B. 2, 112 en 540 (1869); Mém. de Académie de Pétersbourg, VIL Série N° 5 (1870). 
5) Dinglers polytechn. Journal 196, 369. (1870). 
4) B. B. 3, 724 (1870). Zeitschrift für Chemie 1870. 735, 
5) Processen-Verbaal der Kon. Akad. v. Wetenschappen te Amst, vergad. 28 Oct. 1871. 
5) Waaner’s Jahresbericht 1873, 207 uit: Deutsche Industriezeitung 1872, 468, 
7) WrIEDEMANNs Ann. (2) 2, 304. (1877). 
*) Journ, fiir pract. Chemie 19, 322 (1879). 
*) Berl, Akad. Ber, 1880, 225, 
