188G.] NEW YORK ACADEMY OF SCIENCES. 185 



Dr. Ciirnelley, as elsewhere stated, suggests that elements are 

 compounds of hydrogen, with the all-pervading aether of the phy- 

 sicist; but we venture to remark that attempts to explain the 

 nature of elements by assuming them to be compounds of hydro- 

 gen with a substance whose very existence is itself assumed, is, 

 perhaps, an intellectual anuisement, but not likely to advance 

 tlie exact sciences. 



During the past yeai- an Austrian chemist has announced the 

 decomposition of didymium by purely chemical means, and the 

 discovery of ])raseodymium and neodymium as its constituent 

 elements.'" An English chemist claims to have evidence of the 

 existence of an allotropic form of nitrogen."" Both these state- 

 ments await confirmation. 



(8.) The views of chemists concerning the nature of affinity 

 and chemical action are undergoing modifications destined to 

 wield an important influence on the science in the near future. 

 The notion has prevailed, though not distinctly formulated, that 

 the chemical attraction exerted between unlike atoms is a supe- 

 rior sort of cohesion, powerful and absolute; and this force was 

 thought to ojierate between two elementary bodies directly, with- 

 out the intervention of a third kind of matter. That this so- 

 called affinity is radically affected by physical state, by heat, and 

 by electricity has been admitted, but the conviction "is growing 

 in the minds of chemists that many circumstances influencing 

 the union and separation of elements have been overlooked; they 

 are beginning to believe that chemical action does not take place 

 between two substances, and that the presence of a third body is 

 important, if not, indeed, indispensable. Many years ago the 

 word catalytic was coined to describe certain isolated phenomena 

 little understood. These phenomena are familiar to chemists, 

 and the number is increasing; the word catalytic is, however, in 

 disfavor, and the term contiict-aotions is now current. The well- 

 known influence of finely-divided and heated platinum in effect- 

 ing the union of sulphur dioxide and oxygen, and the action of 

 metallic silver in decomposing ozone without itself undergoing 

 any change are examples. In these and similar changes one of 

 the substances indispensable to the reaction remains unchanged, 

 and its lole cannot be expressed in equations. 



Dulong and Thenard,"' more than sixty yeai-s ago, showed that 

 the temperature of ignition of a mixture of hydrogen and oxy- 

 gen is lowered to a remarkable degree by the presence of solid 

 bodies of varied nature. Within a few months, Menschutkin 

 and Konowalow "" have made a study of the influence of asbes- 

 tus, glass, and other bodies on the decomposition-temperature of 

 many organic compounds. 



There is another class of reactions in which one body acts 



