288 PROCEEDINGS OF THE AMERICAN ACADEMY 



Grama. 



"Weight of platinum crucible = 18.0889 



" crucible + CuO, 2^ hours at dull redness = 19.6o8o2 



« " " 4 hours more " = 19.6584G 



After ignition at very bright redness (20 minutes) = 19.6574 



" " (50 m. more) =19.6571 



Total loss of weight = A)014 



One gram of this specimen was shown to contain 0.00081 gram of 

 <iccluded gas before ignition, and 0.00039 gram afterward (Experi- 

 ments 86 to 95). In the quantity taken above this difference corre- 

 sponds to a loss of weight of nearly 0.0007 grams, or about half of 

 that observed. The remainder of the loss may have been due to a 

 partial reduction of the oxide. (Compare page 275.) 



Experiment 102. — In order to discover if heating cupric oxide in 

 a vacuum produced any important evolution of nitrogen, six grams of 

 cupric oxide were dried in a glass tube with the greatest care, exactly 

 after the manner of Hampe, and weighed in the air. One end of the 

 tube was then sealed, the other was attached to a Sprengel pump, and 

 the whole was heated to about 500° C. for half an hour. Upon seal- 

 ing and weighing; the loss of weight was found to amount to 4.4 milli- 

 grams. The amount of air displaced was found by opening the tube 

 under boiled water, which wholly filled it. The weight of water, 

 reduced to 4°, was 3.48 grams, while the temperature and pressure 

 of the air at the time of weighing the exhausted tube were respectively 

 24° C. and 754 mm. Hence the weight of displaced air must have 

 equalled 4.1 milligrams, or only 0.0003 gram less than the loss of 

 weight actually observed. Therefore the cupric oxide could not have 

 lost more than 0.005% of its weight under the treatment described.* 

 The moist cupric oxide yielded approximately the usual volume of 

 nitrogen upon solution in acids ; but no very accurate measurement 

 was made. 



It has been said that these experiments were intended onlv for 

 rough comparison. Since it appeared possible to apply a correspond- 

 ing correction to the atomic weight of copper deduced from tin- oxide, 

 it became importatit to make a more accurate series of determinations. 

 The cupric oxide used in these final experiments represented tln-ee 

 different specimens, similar to or identical with those used in Nos. 

 43, 45, 48, and 49. 



* In IvNixrimont 50 the temperature of ignition was somewhat liiglier. 



