378 Foreign and Miscellaneous Intelligence. 



was covered witli metallic copper, whilst the positive conductor 

 evolved bubbles of gas. Having replaced the latter conductor by one 

 of silver, it soon became covered with a yellow film gradually changing 

 to violet, which was considered as chloride of silver. The expe- 

 riment was repeated with the iodides of zinc and iron ; the platina 

 poles had scarcely touched the solutions before the iodine, with its 

 distinctive colour, appeared at the positive pole, and the metals were 

 reduced and deposited upon the negative pole. 



' After these experiments it appears,' says M. Matteuci, c that we 

 may affirm with certainty, that these combinations, even when dis- 

 solved in water, do not change in their nature, and are not converted, 

 as is often imagined, into muriates, hydriodates, &c. of the oxides of 

 the metals present.'* 



4. VOLTAIC TEST OF THE STATE OF METALS. 



It is well known that Dr. Wollaston devised a beautiful little ar- 

 rangement to ascertain the conducting power of certain crystals 

 having metallic characters, and which ultimately proved to be 

 titanium. If a plate of copper be in contact with a plate of zinc, 

 and part of both plates be immersed in a dilute acid, the copper, by 

 its electric condition, decomposes water and becomes covered with 

 bubbles of hydrogen. If a piece of paper, or a card, be interposed 

 where the two metals were in contact, the copper loses this power 

 altogether, and no bubbles appear on it ; but if a small hole be made 

 in the paper or card, and a little piece of metallic matter put there, 

 so as to touch at once both the zinc and copper, then the latter has 

 its full power restored. 



M. Macaire Prinsep has applied this test more generally ; and he 

 found, in the first place, that a metal was necessary to restore the 

 effect lead, bismuth, tin, &c. reproduced the bubbles ; but sulphuret 

 of arsenic, rutilite or oxide of titanium, grey cobalt ore, and the 

 sulphurets of antimony, iron, tin, or lead, produced no effect. Por- 

 tions of meteoric stone from Aigle and Barbotan, by producing 

 bubbles, showed that they contained uncombined metal ; and the 

 method seemed competent to indicate, in all cases, whether the 

 metals used were free, or in a combined condition. 



As lead gave bubbles, but the sulphuret of lead none, experiments 

 were made with lead, to which sulphur, in increasing proportions, 

 had been added : T ^, ^, J^, T \ r , and T L o f sulphur did not take 

 away the property from lead ; but when l of sulphur was used, no 

 bubbles appeared upon the copper. Then ascertaining the propor- 

 tions in the definite sulphuret of lead, he found them to be exactly 

 those which caused the evolution of bubbles to cease (86 lend 

 and 14 sulphur.) The same effect occurred with the sulphuret 

 of tin ; and hence it was concluded that chemical combination in 



* Bib, Univ. li>30, p, 138. 



