Intelligence and Miscellaneous Articles. 141 



under the same conditions, in the molecules of air. The laws of 

 Mariotte and G-ay-Lussac, established solely upon three simple 

 gases, are therefore inapplicable either to iodine or to the other 

 halogen elements. 



This is the place to mention that the law of specific heats is 

 no more applicable than the above-rnentioned to this group of ele- 

 ments : for the specific heats of gaseous chlorine and bromine exceed 

 by one fourth those of the other simple gases, and that between the 

 ordinary temperature and 200° C, temperatures at which dissocia- 

 tion cannot be admitted. 



It hence follows that the increase of the total energy of the halo- 

 gen gases with the temperature exceeds that of the three other 

 simple gases hitherto investigated (nitrogen, oxygen, hydrogen), as 

 well as the increase of the vis viva of translation : these two orders 

 of effects seem to be correlative. 



Moreover, the diminution of density of iodine gas being progres- 

 sive, the same is the case with the augmentation of its vis viva of 

 translation ; and, as M. Troost very judiciously remarks, this does 

 not permit us to draw any correct conclusion respecting the varia- 

 tion of the number of the molecules ; that sort of reasoning becomes 

 arbitrary the moment the weight of the molecule of iodine, viewed 

 either at a high temperature or at a low pressure, eludes the old 

 definitions. 



Only one law remains applicable to the elements, possessing an 

 absolute and universal character; it is the invariableuess of the 

 proportions by weight in which the elements combine with one an- 

 other. That is now the only immovable foundation of chemical 

 science. — Comptes Bendus de VAcademie des Sciences, July 12, 1880, 

 t. xci. pp. 77, 78. 



ON THE DENSITY OF THE VAPOUR OF IODINE. BY L. TROOST. 



The highly important researches published by M. Y. Meyer on 

 the variation of the density of iodine-vapour at very high tempera- 

 tures, and the results obtained by MM. Crafts and Meyer which 

 confirm them, have decided me to take up those densities again, 

 with the apparatus made use of by M. H. Sainte-Claire Deville and 

 myself for the vapour-densities of selenium and tellurium, and in 

 which we determined the temperature with the aid of the air-ther- 

 mometer*. 



I have employed, as in those old experiments, balloons of porce- 

 lain, glazed inside and outside, and of a capacity of from 250 to 

 300 centims. They are tared with the little porcelain stopper, 

 which at the moment of closing will be fused at the oxyhydrogen 

 blowpipe. 



* The supposition which has appeared in a recent publication, that we 

 did not employ the air-thermometer for the determination of temperatures 

 above that of the boiling-point of zinc, is erroneous. 



