OF ARTS AND SCIENCES. 287 



The liiglier temperatures recorded above are merely approximate 

 guesses. GOO^ signifies a dull red heat, 700° a medium red heat, and 

 900° a very bright red heat. In Experiment 92 the oxide was 

 heated at the highest temperature obtainable by a Berzelius spirit 

 lamp. In No. 94 the material was heated for an hour and a half in 

 the Berzelius lamp, and then for an hour in a glass tube under a 

 stream of oxygen. The oxide was transferred while warm to the 

 bulb apparatus. It evolved upon solution 0.088 per cent of gas, one 

 eighth of which was oxygen. In the ninetieth experiment hydro- 

 chloiic acid was used for the solution of the oxide. 



The two series of determinations, which were perhaps more numer- 

 ous than necessary, showed the following important facts: — 



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. (Nos. 58, 63-67, 84-94.) 



Second, that ignition of the oxide at very bright redness was ca- 

 pable of expelling a portion of this gas. The temperature required 

 was nevertheless considerably above that which Hampe apparently 

 employed. (Nos. 59, 81, and 95.) 



Tiiird, that beyond a certain limit the time of ignition makes no 

 important difference. (Nos. 86-91.) 



Fourth, that the gas was not absorbed from the air on cooling. 

 (Nos. 64, 65, 66, and others.) 



Fifth, that specimens of cupric oxide prepared in different ways 

 contained very different amounts of gas. It is a curious fact that 

 material which has been heated only to 300° contained less gaseous 

 nitrogen than that which had been ignited at a higher temperature. 

 In this case the nitrogen may still have existed in the combined form. 

 (Nos. 78, 79, 84, 85.) 



An explanation for the observed phenomena must necessarily be 

 hypothetical, and will not be attempted at present. 



In order to find the direct connection between the loss of weight 

 noticed upon heating cupric oxide and the quantity of gas retained by 

 the substance, the following experiment was made. 



Experiment 101. — Cupric oxide which had been heated to constant 

 weight at dull redness was ignited at bright redness in a double 

 platinum crucible. 



