RICHARDS. RETENTION AND RELEASE OP GASES. 417 



Cu(N03)2 . 3 CuO 1^ 4 CuO + [N-A] 



Vapor. Vapor. 



it It 



Cu(N03).2.3 CuO 4 CuO 



SoUd. Solid. 



It is probable that Graham's basic cupric nitrate Cu(N03)2 . 3 Cu(0H)2 

 is dehydrated before the nitric acid begins to leave ; if it is not, of course 

 three molecules of water must be added to the products above. The 

 addition of the water does not affect the essential point in the follow- 

 ing logic, however, ^he gaseous products of this reaction attain a 

 pressure of 760 millimeters at about 280°. 



The reaction represented above is evidently only a preliminary stage 

 of the whole change ; it may have scarcely begun, or may have run 

 almost to an end in some cases before the dissociation of the nitric 

 anhydride begins to enter into the problem. This dissociation may 

 be complete, resulting in a mixture of the elementary gases, or it may 

 (and does at ordinary pressures) stop at one of the lower oxides of 

 nitrogen. Since the gases, whatever they may be, are necessarily held 

 in microscopic cells, while their own volume under ordinary pressure 

 is several times that of the total volume of the solid containing them, it is 

 obvious that the pressure under which they exist must be very great. 

 At tliis great pressure the stability of NoOj must be very considerably 

 increased, for the reaction 2 NoOj = 2 No + 5 Oj is one which pressure 

 must seriously affect because of the change of volume concerned in it ; 

 but more probably the peroxide of nitrogen may be the first product of 

 the reaction. In any event, it is evident that the complete separation of 

 the oxygen and nitrogen does not take place immediately, for much less 

 nitrogen was yielded by the specimens of each oxide heated for a short 

 time at comparatively low temperatures than by like specimens heated 

 longer or hotter. 



Both of these reactions, the decomposition of the cupric nitrate as well 

 as that of the oxides of nitrogen, evidently then require time for their 

 completion, so that the maximum of gas contents is not immediately 

 attained. Besides being accelerated by heat they are also possibly 

 both hastened by the escape of a portion of the oxygen, an interesting 

 phenomenon which occurs side by side with the decomposition. To 

 make the matter clearer, let us represent the dissociation of the oxide 

 of nitrogen by the general formula 



2 NO, = N. + XO2. 

 VOL. XXXIII. — 27 



