820 Mr. F. B. Yoiras on th 



o 



ie 



opalescence became narrower simply owing to the increase in 

 the slope or' density through the transition zone, produced by 

 the fall in temperature ; when uniformity of density was 

 produced by stirring, the opalescence likewise became uniform 

 and showed no tendency to become localized. The opalescent 

 effects produced without stirring were very much like those 

 produced in tube XIY. with the aid of the heating-coil, but 

 were far more lasting. 



It is necessary to observe caution in applying the results 

 obtained with one substance to the explanation of phenomena 

 observed in another. So far, however, as this may be done, 

 it seems probable that the phenomena observed in tubes of 

 carbon dioxide by Dwelshauvers-Dery might readily be pro- 

 duced if the experimental substance contained strong traces 

 of some much more volatile impurity. It is unnecessary to 

 regard the opalescent zone as a zone of separation of impurity 

 from the ether, or the opalescence as consisting of the 

 impurity in suspension. The opalescence is conditioned by 

 the diffusion of the impurity only in so far as such diffusion 

 produces a graduation of density in the substance, and hence 

 the intensity of the opalescence or the bulk of opalescent 

 material may be altogether out of proportion to the quantity 

 of impurity present. 



H. The Liquidogenic Theories. 



Though it cannot be claimed that the experiments recorded 

 by any means settle the liquidogenic controversy, yet they 

 have some evidential value. 



Travers and Usher (7) have criticised experimentally the 

 results of Battelli by means of which he showed that, in the 

 case of ether, 6 C decreases progressively as the mean density 

 of filling increases. It is to be observed that the mean den- 

 sities of filling chosen by Travers and Usher were contained 

 within much narrower limits (0* 244-0*281) than those taken 

 by Battelli (0*2409-0-3043). Though the former investi- 

 gators do not explicitly state the fact, one's own observations 

 lead to the conclusion that if the tubes approaching the 

 higher limit taken by Battelli were filled with ether sensibly 

 pure and free from permanent gas, it would be impossible to 

 make the meniscus disappear within the limits of the tube 

 without raising the temperature of the thermostat so rapidly, 

 in order to exaggerate the Villard effect, as to make accurate 

 observations impossible. In tube XIII. it was found that 

 with sufficiently slow rise of temperature the meniscus rose 

 to within *5 cm. of the top of the tube, though the mean 



