216 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



a-raodification, is obtained by dissolving the crude product 

 in warm alcohol and allowing it to cool. At first an oil sep- 

 arates, in which after a time crystals aj^pear, which may be 

 developed into thick prisms on repeating the operation. 

 These prisms are monoclinic twins, with a well-defined 

 cleavage, having the plane of the optic axis perj^endicular to 

 the plane of symmetry. They show strong negative double 

 refraction, and fuse at 36.3 Centigrade. Any of the other 

 forms when melted crystallize in this form on touching the 

 liquid with a crystal fragment of it. The second, or /3-modi- 

 fication, is obtained by fusing the former completely at 39 

 to 40, and allowing to cool. Long concentric groups of 

 prisms are formed, which are monoclinic, but which are with- 

 out cleavage, have a different axis ratio and axis angle, and 

 fuse at 37.1. Crystals of a after five weeks yield /3 on crys- 

 tallization from alcohol. The third, or y-modification, crystal- 

 lized out of the aqueous solution into which the mixture was 

 poured in preparing the substance. It is also the most per- 

 manent form of all, both a and /3 being converted into 

 it in a few weeks, though becoming turbid in twenty-four 

 hours. The crystals are orthorhombic, show a distinct cleav- 

 age, and have a moderate but positive double refraction. 

 They fuse at 38.8. The liquid modification is obtained 

 whenever either of the solid forms is heated to 42. On cool- 

 ing it remains permanently liquid. In accounting for this 

 physical isomerism, Laubenheimer assumes Naumann's hy- 

 pothesis that physical molecules are formed by the aggrega- 

 tion of chemical molecules, and believes that the larger the 

 number of chemical molecules the more stable the body. The 

 fusing-point of the body containing the less complex physical 

 molecule is therefore lower, the specific gravity is less, and 

 specific heat is greater. 35 (7, IX., June, 1876, 760. 



THEEMO-CHEMISTRY OF OZONE. 



Berthelot has studied thermo-chemically the formation of 

 ozone. Pure and dry oxygen was passed through a tube 

 where it was subjected to the influence of the silent electric 

 discharge, and then into a calorimetric flask containing 500 

 cubic centimeters of a solution of arsenous acid in hydro- 

 chloric acid, previously graduated. At the end of twenty to 

 thirty minutes, six to nine liters of oxygen had passed through 



