278 



PROCEEDINGS OF THE AMERICAN ACADEMY 



The average of results so heterogenous in nature can naturally have 

 no important meaning, but it is interesting to note the approximation 

 to the old value of the atomic weight. The high value given in Experi- 

 ment 48 is manifestly only a compensation of errors. From Experi- 

 ments 48 and 49, the only two in which both materials were ignited 

 at a bright red heat, 2.97909 grams of cupric oxide yielded 2.37811 

 grams of metallic copper. Computiug from these data the atomic 

 weight of copper, we obtain the value 63.313, which is comparable with 

 the result 63.312 obtained indirectly through the synthesis of the sul- 

 phate as well as with the number 63.346 fixed upon by Hampe. The 

 absolute identity of the first two figures must be attributed to chance, 

 since the agreement of the individual results was not perfect. 



These results again pointed to the existence of a volatile impurity 

 in cupric oxide, but no proof was afforded that the impurity was 

 wholly driven off at the temperature of fairly bright redness. The 

 determination of this point, as well as of the nature of the occluded 

 material, became a matter of great importance. 



Tests for Impurities- 



The first hypothesis suggested was the possible imprisonment of a 

 small amount of water.* To subject this hvpothesis to proof, pure 

 cupric oxide might be dried at a red heat, and reduced by means of 

 carbon monoxide, when of course any occluded water would be set free 

 and mijjht be weighed. 



The cupric oxide used in the execution of this plan was some of 

 that which remained from the oxygen research. It hud been prepared 

 in the usual manner. The carbon monoxide was made from oxalic 

 and sulphuric acids, and after a preliminary purification with caustic 

 potash the gas was collected over water in a glass gasholder. From 

 this receptacle it was passed through very large amounts of potassic 

 hydroxide, over calcic chloride and red hot platinum sponge, and 

 finally through a flask containing sulphuric acid and two tubes con- 

 taining phosphorus pentoxide, before being allowed to come in contact 

 with the material to be reduced. 



In Experiment 53, — which may be taken as a type, — fifteen 

 grams of the cupric oxide contained in a hard glass tube were dried 

 at a red heat in a stream of pure air for forty-five minutes. A small 

 weighed phosphoric oxide tube was then connected at the exit, and 

 the current of air was continued for over an hour. 



* See MuUer-Erzbacli, Jahresbericht, 1885, p. 74. 



