RICHARDS. — RETENTION AND RELEASE OF GASES. 407 



" First, that cupric oxide prepared by the ignition of the oxynitrate 

 after Hampe's method contained between four and five times its volume of 

 occluded gas. 



" Second, that ignition of the oxide at very bright redness was capable 

 of expelling a portion of this gas. The temperature required was never- 

 theless considerably above that which Hampe apparently employed.'^ 



The recent experiments add to these conclusions only greater definite- 

 ness. It is now clear that nearly all the gas is retained until a tempera- 

 ture of slightly over 860° is reached, when more than nine tenths of it 

 is rapidl}^ set free. Somewhat above this point the cupric oxide is itself 

 partly decomposed ; and in the neighborhood of 1000° the mixture of 

 cupric and cuprous oxides fuses first into a mass resembling scoria, 

 and then into a limpid fluid. It is evident that Scott must have used 

 in his muffle a temperature somewhere between 850° and 1000° ; for 

 he found on the average 0.055 c. c. of gas per gram of cupric oxide, 

 while my results obtained by means of temperatures in this neighbor- 

 hood average 0.05 c. c. Moreover, some of his material was slightly 

 reduced, but apparently none of it was melted. 



It was clearly shown in the previous papers that the low results given 

 by material ignited at temperatures below 450° are due to the presence 

 of undecomposed cupric nitrate, which by its decomposition at higher tem- 

 peratures yields the gas forming the subject of the present discussion. 



The fact that prolonged ignition does not affect the amount of gas 

 occluded may be inferred from the experiments just recorded ; but in 

 order to obtain more definite information on this influence of time, 

 a third series of experiments was made. 



The Effect of Time of Ignition on the Total Amount of 

 Gas occluded by Cupric Oxide. 



Temperature : The Fusing Point of Thallous Sulphate, about 640°. 



(26) 1 gram of CuO, after ignition for 10 minutes, gave 0.56 c.c. gas. 



(27) " " « 0.57 " 



(28) « « " 0.53 " 



Average 0.55 c.c. gas. 



(29) 1 gram of CuO, after ignition for 5 hours, gave 0.56 c.c. gas. 



(30) " " " 0.59 " 



Average 0.57 c.c. gas. 



(31) 1 gram of CuO, after ignition for 20 hours, gave 0.56 c.c. gas. 



(32) " " " 59 " 



Average 0.57 c.c. gas. 



