210 



SCIENCE 



[N. S. Vol. L. No. 1287 



/OH 



NHo + HNO3 -> O = N^OH , 



but this compound is unstable and it loses 

 water to form HjIST^O, 



/OH 

 HjO + O = N<; 



/OH 

 O = N^OH 



^NH, 



> 



NH 



and finally this HjlST^O loses another molecule 

 of water to form O = IT ^ N" in which one 

 atom of nitrogen has a negative valence of 

 three and the other a positive valence of five 

 as in the original molecule of annnonium 

 nitrate. In other words, neither atom of 

 nitrogen has experienced any change with re- 

 gard to its state of oxidation. 



This hypothesis is certainly no more diffi- 

 cult to understand than many hypotheses 

 which have been advocated in the past by 

 chemists in both the so-called " organic " and 

 " inorganic " fields. It is objectionable, how- 

 ever, because it assumes the formation of two 

 very unstable, hypothetical, intermediate prod- 

 ucts. These intermediate compounds are cer- 

 tainly not very well known and there appears 

 to be no proof of their formation during the 

 progress of the reaction in question. Such a 

 hypothesis is in line with the assumption of 

 " nascent hydrogen " being formed when a 

 chemical reduction is accomplished by a 

 metal far above hydrogen in the electro- 

 motive series and it reminds one of the 

 " primary products " which electro-chemists 

 formerly believed to be formed as a result of 

 electrolysis. 



Such an explanation, moreover, is contrary 

 to the evidence which can be deduced from the 

 behavior of other ammonium salts upon igni- 

 tion. It loses sight of the fact that nitrogen 

 in its lowest state of oxidation is relatively un- 

 stable and easily oxidized and of the fact that 

 nitrogen in its highest state of oxidation is 

 easily reduced. In general, when an element 

 is present in a compound in two states of oxi- 

 dation, the decomposition of the compound is 

 likely to result in the element assuming a state 

 of oxidation intermediate between the two 

 states in which it previously existed. 



"When ammonium dichromate is heated, 

 nitrogen gas is evolved and chromic oxide is 



left behind. Heating ammonia sulfate re- 

 sults in the formation of nitrogen and stilfur 

 dioxide. When ammonium nitrate is heated 

 one atom of nitrogen is oxidized to form free 

 nitrogen and the other is reduced to form 

 nitrogen. In this case, Noyes would assume 

 that neither atom of nitrogen is affected by 

 oxidation or reduction but does not all our 

 information with regard to the stability of 

 .ammonia and of nitroiis acid make it seem 

 simpler to assume that the polarity of nitrogen 

 is zero when in the free condition rather than 

 to insist that one atom has a positive valence 

 of three and the other a negative valence of 

 three? 



Finally, 'Nojea claims that his formula 

 seems more in accord with the ease with which 

 nitrous oxide gives up its oxygen. As one 

 writes the formula on paper it seems very 

 easy to take away the oxygen from the 

 O ^ N" ^ IN" molecule and " organic " chemists 

 always love to get atoms on the blackboard 

 where they can easily erase them to show stu- 

 dents how new compounds are formed, but it 

 isn't quite clear why ammonium nitrate should 

 withstand strong ignition without any effect 

 upon the state of oxidation of either atom of 

 nitrogen and yet after undergoing all this 

 severe treatment, with the nitrous oxide re- 

 taining one nitrogen like that of nitric acid 

 and the other like that of ammonia, be very 

 susceptible to reduction. It would seem far 

 sim.pler to assume that nitrogen with a valence 

 of one is easily reduced. 



The writer has respect for the views of Pro- 

 fessor ISToyes and has been under obligation to 

 him in the past for helpful advice. He re- 

 joices to learn that Professor ISToyes is willing 

 to accept much of the modern theory of 

 valence. William T. Hall 



Cambridge 



a snow effect 

 To THE Editor of Science: On March 3 of 

 the present year a very interesting snow effect 

 occurred in Orono and vicinity, which is per- 

 haps worth recording in the colimins of Sci- 

 ence. The writer has not been able to find any 

 one who ever saw a similar effect, and it 



