M. H. Rose on a new Series of Metallic Oxides, 369 



was effected. After the longer tube of the water-bottle had been 

 connected with the longer tube of the bottle which contained the 

 precipitate, the hydrogen apparatus was connected with the 

 shorter tube of the water-bottle. The cock of the hydrogen 

 apparatus, and then the pinchcocks, were successively opened, 

 beginning with the one nearest the hydrogen apparatus. The 

 flask with the precipitate was filled in this way with boiled-out 

 water, which was forced out of the vessel in which it was con- 

 tained by hydrogen. After the wash- water had been mixed with 

 the precipitate by repeated shaking, the precipitate was allowed to 

 settle in order to repeat the operation. To the wash-water, boiled 

 hydrate of potash solution was added until no more tin could be 

 discovered in the wash- water drawn off. But this could not be 

 completely attained even by often repeated washing. Hence 

 when only traces of tin could be detected in the wash-water, the 

 hydrate of potash was washed out until the precipitate no longer 

 settled down well after washing. Ammonia was then added to 

 the wash-water, and the washing completed. 



Although the hydrogen was liberated as pure as possible, 

 before passing into the apparatus it was led through a tube 

 which contained pumice saturated with a concentrated solution 

 of pyrogallate of potash. This precaution is by no means 

 unnecessary, because air diffuses into the apparatus from the 

 dilute sulphuric acid. 



In order to obtain small quantities of the precipitate for the 

 various experiments, the larger tube in the flask was depressed 

 to the bottom through the precipitate, and by means of the 

 hydrogen current some of the precipitate mixed with water was 

 forced either into small flasks or into a flask arranged like that 

 with the precipitate, and which was closed by the wash-water. 



But notwithstanding all care, the preparation of a pure sub- 

 stance was not always successful, but instead of it a mixture of 

 copper and of semioxide and isoxide of copper was frequently 

 obtained. All the causes of failure have not been accurately 

 ascertained ; but they undoubtedly lie in the temperature and 

 concentration of the solutions taken. But if the preparation of 

 the compound has been successful, it may be kept under water 

 and protected against the access of air without being in the 

 slightest degree changed. 



If the compound has been kept for some time under water 

 with entire exclusion of air, it becomes gradually denser, and 

 more indifferent to oxidation. 



For the purpose of analysis, a mixture of the compound with 

 water was forced, in the manner described above, into a flask 

 which contained dilute sulphuric acid. The compound was 

 immediately decomposed : while metallic copper was deposited. 



