4 JOURNAIy OF THE 



proportion of the insoluble residue decreases rapidly in 

 either direction from these temperatures. Some insol- 

 uble residue is produced at all the lower temperatures 

 but none is produced when the reaction takes place at 

 270" C. and lasts for onl}^ a few seconds. 



Berzelius^ noted this black substance when copper 

 was treated with concentrated sulphuric acid. He said 

 it appeared to be a subsulphate because it was oxidiza- 

 ble by nitric acid. He made no quantitative determi- 

 nations to show its composition. Such a body would 

 contain fifty-seven per cent, of copper and in no case 

 did I find the black residue to contain less than 67.64 

 per cent. 



BarrueP found that sulphuric acid acted on copper 

 at ordinary temperatures if sufficient time were given. 

 He claimed that the sulphur dioxide produced was dis- 

 solved in the acid and attacked the copper forming- cop- 



1 Traite de chimie 4. 324. 



2 Journ. de Pharni. 20. 13. 1834. 



