200 On definite Proportions. 



rate result, because some of the copper is dissipated during 

 combustion, or is carried away during the oxidation by 

 nitric acid, together with the vapours which are emitted. 

 The fou'-th and fifth experiments appear to be the nearest 

 to the truth, but they require a correction which I cannot 

 determine with perfect accuiacy. It is well known that 

 all copper contains carbon and a little sulphur. If we as- 

 sume that these together make | per cent, of ihe weight of 

 the copper, the quantity of oxygen which the experiments 

 indicate is so much too small, and '05 gr. rpust be added 

 to it for 10 gr. of copper, the mass of the copper being 

 diminished in this proportion during the oxygenization. 

 Since then 100 parts of copper, in experiment 5, received 

 the addition of 24*5 parts in weight, we may assume that 

 pure copper would have lakcii up 25 of oxvgen, and tha^ 

 the oxide of copper, in round numbers, is composed of 



Copper 80 100 



Oxygen 20 25 



B. Protoxide of Cupper. 



Ten grammes of oxide of copper were mixed with an 

 equal weight of the pure copper dust already mentioned, 

 and 75 grammes of concentrated muriatic acid were poured 

 on them in an air-tight vessel. The mixture remained 

 three days standing on a warm stove, and was shaken from 

 time to time. The undissolved copper was placed on a 

 filter, washed, and hastily dried on a plate of ca>t iron: it 

 ■weighed 1*97 grammes. Consequently 803 gr. of copper 

 had been dissolved at the expense of the oxygen contained 

 in the oxide. Now the oxide contained also ei^ht gr. of 

 metal ; consequently the protoxide now formed, and dis- 

 solved in the acid, contained twice as much metal as the 

 oxide. The difference of '03 gr. in the experiment arose 

 probably froin the operation of the concentrated acid on 

 the copper, by means of which a little hvdrogen gas was 

 produced, which was forced out with some violence when 

 the vessel was opened. Hence it follows that 100 parts of 

 copper, in order to become a protoxide, take up, according 

 to the experiment, 12"3 parts, and according to the calcu- 

 lation, ]2*5 parts of oxygen ; and the protoxide of copper 

 consists of Copper S8-89 100 



11-11 12-5 



Mr. Chenevix found, in a similar experiment, the quantity 

 of oxygen a little greater, that is 11*5 per cent, or 13 to 

 100 parts of copper. 



If we calculate the oxygen of the protoxide of copper ac- 

 cording 



