454 SCIENTIFIC RECORD FOR 18S4. 



(l.ita are at hand for the calculatioD of the coefficient of the solid {G 

 R., March, 1884, xcviii, 020.) 



As long ago as 1867 Govi had propounded the hypothesis that the 

 contraction which takes place when stretched rubber is beated was due 

 to the exjiansiou of the gas contained in its pores. When the caout- 

 chouc is stretched the spherical cavities elongate; and on heating, the 

 gas dilates more than the solid, and tends to make the ellipsoidal cavi- 

 ties spherical again, thus shorteniug the rubber. Hesehus has tested 

 this hypothesis by performing the experiment in vacuo. Placing the 

 stretched caoutchouc under an exhausted receiver, the expansion of 

 the air due to diminished pressure should have the effect of shortening 

 the rubber. But not tbe smallest effect was observed. {J. Soc. Phys. 

 Chim. Russe, xv, 103; J. Phys., October, 1884, II, ill, 459.) 



Fromme has made an investigation into the changes produced in the 

 molecular condition of iron by heating to redness and cooling. He con- 

 cludes that in the tempering of a steel bar, besides the mechanical and 

 purely physical process of suddeu coutraction, auother change, also of a 

 chemical nature, takes place, this consisting in a combination between 

 the free carbon and the iron. {Phil. Mag., December, 1884, xviii, 473.) 



Gernez has studied the duration of the solidification of surfused sul- 

 phur in both the prismatic and octahedral forms, and finds that the time 

 required for the latter to solidify is much longer, in some cases 100 

 times, than the former. During these experiments he succeeded in ob- 

 taining a third form of crystal, in long prismatic rods with a nacreous 

 luster. Hence he concludes that the measurement of the velocity of 

 solidification constitutes a new method of investigation, which applied 

 to sulphur developed some unexpected facts, such as the modifications 

 produced at constant temperature under the prolonged influence of heat, 

 and the order of transformation under various conditions. {J. Phys., 

 II, III, 58, 286, February, July, 1884.) 



E. Wiedemann has experimented to determine the change in volume 

 which metals and their alloys undergo on fusion. He used a thermom- 

 eter containing the metal to be examined, in the form of a cylinder, sur- 

 rounded with oil. The points of solidification were determined by the 

 method of cooling. Zinc melts at 226° and increases in volume at the 

 moment of fusion, this increase being from 1.7 to 2.2 per cent., according 

 to the specimen. Plumber's solder increases in volume also about 2 per 

 cent. Lead-bismuth alloys of various compositions show two different 

 points of fusion, to each of which corresponds a notable increase of vol- 

 ume, but which, however, is not sudden. ( Wied. Ann., xx, 228; J. Phys., 

 II, III, 148, March, 1884.) 



Eaoult has examined the laws of congelation in solutions, and con- 

 firms essentially the principles established by Blagden in 1788. The 

 conclusion reached is enunciated in the following general law : A mole- 

 cule of any compound whatever, in dissolving in 100 molecules of any 

 liquid whatever, different in character, lowers the solidifying point of 



