408 PROCEEDINGS OP THE AMERICAN ACADEMY. 



A portion of the last specimen, which had been heated for twenty 

 hours, was further ignited for five hours at about the fusing point of 

 common salt (about 800°). Upon solution in acid this portion yielded 

 the same amount, 0.59 c. c. of gas. Thus another of the conclusions 

 arrived at in 1892 is confirmed : — 



"Third, that beyond a certain limit the time of ignition makes no im- 

 portant difference . " 



This is true, however, only below 850°. Experiments 20 to 22 show 

 that when the imprisoned gas has once begun to be set free, at tem- 

 peratures above 850°, the time is an essential factor ; and that when 

 sufficient time has been allowed, the expulsion of the gas is almost 

 complete. Scott examined only cupric oxide from which he had thus 

 expelled the gas. 



In this connection it is interesting to note that Morse and Arbuckle * 

 have recently verified, with apparatus far more elaborate and exact than 

 ours, the results of Rogers and myself concerning the amount of gas 

 occluded by the oxide of zinc.f Considering the fact that the manner 

 of preparation of the substance undoubtedly affects the amount of gas 

 retained, the closeness of the agreement is surprising. Only one of their 

 conclusions is difl^erent from ours : in their opinion, there is no reason 

 to believe that the temperature of ignition of the oxide has any effect 

 on the composition of the occluded gas, while in our experiments the 

 imprisoned oxygen decreased with increasing temperature. The basis 

 of their reasoning is the supposition that the total amount of gas re- 

 tained is dependent solely upon the temperature ; using this total amount 

 as a thermometer, they point out the fact that the smaller amounts 

 of gas obtained in their experiments did not always contain the smaller 

 amounts of oxygen ; and hence they conclude that the temperature is 

 not an essential determining cause of the composition of the mixture. 

 In a letter answering some questions about the matter. Professor Morse 

 kindly writes " We made every effort to secure constant temperatures 

 for our oxide, giving the closest attention, to that end, to every detail 

 of the firing of the furnace, the fuel, the location of the crucibles," etc. 

 Since this is the case, and I cannot doubt the essential success of their 

 efforts, it seems to me that their results have but little bearing upon the 

 effect of varying temperatures on the oxide. The fact that their mixture 

 of gases was by no means constant in composition is better explained 

 by the supposition that some other cause besides the temperature influ- 



* Amer. Chem. Journal, XX. 195. t Tliese Proceedings, XXVIII. 200. 



