412 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Tliird Series : Just above the Melting Point of Sodic Sulphate. 



(49) 1 gram of ZnO, heated at 880"^ for 3 minutes, gave 0.49 c.c. gas. 



(50) 1 gram of ZnO, heated at 880° for 5 minutes, gave 0.35 c.c. gas. 



(51) 1 gram of ZnO, heated at 880° for 12 minutes, gave 0.29 c.c. gas. 



(52) " " " 0.25 " 



Average 0.27 c.c. gas. 



(42) 1 gram of ZnO, heated at 880° for 30 minutes, gave 0.19 c.c. gas. 



(43) " " " 0.19 " 



Average 0.19 c.c. gas. 



(38) 1 gram of ZnO, heated at 880° for 180 minutes, gave 0.14 c.c. gas. 



(39) " " " 0.1 8 " ' 



Average 0.16 c.c. gas. 



In each of the series the same fact may be noted, — the fact that con- 

 tinued heating at any one temperature is capable of causing a slow 

 evolution of gas from the oxide. Only in the second of these series is 

 evident an initial increase in the amount of gas, indicating a maximum 

 after less than twenty minutes of heating. This increase, which is 

 manifestly due to the advancing decomposition of the traces of im- 

 prisoned nitrate, undoubtedly ceases after an hour's heating at 660°, 

 or after three minutes' heating at 880° ; hence it does not appear 

 in the first and third series. 



The steady loss of gas after this maximum has been attained — a loss 

 increasing with time as well as with increasing temperature in the case 

 of zincic oxide — is worthy of further attention, especially because it will 

 be remembered that the amount of gas retained by cupric oxide re- 

 mained almost constant until a very high temperature was reached. 

 Analysis of the several speciinens of gas showed at once wherein lay 

 the explanation ; for they showed as before that the maximal quantities 

 of gas consisted chiefly of oxygen; while the gas obtained by the last 

 two experiments consisted chiefly of nitrogen. Here again the nitrogen 

 remained nearly constant, only diminishing from 0.20 c. c. at the max- 

 ima to about 0.13 c. c. at the minima ;• while the oxygen diminished in 

 the same samples from 0.21 c.c. to 0.03 c.c. 



It remains only, as far as zincic oxide is concerned, to show how 

 wide a difference in the amount of gas may be caused by the original 

 mode of preparation of the solid material. 



