230 Intelligence and Miscellaneous* Articles. 



wires of their effect. The metals which acquire this property in the 

 highest degree are zinc and iron, next to which is gold. He attempts 

 to explain the phenomenon by supposing that the continued passage 

 of the electrical stream had brought the elements of the water nearer 

 to a state of separation, so that a very slight influence was sufficient 

 to destroy their union. It must be confessed, however, that we 

 cannot at present advance a satisfactory explanation. — Berzelius, 

 Arsberattelse, 1829, p. 33. — Brewster's Journal. 



DETECTION OF ALLOY IN SILVER BY THE MAGNETIC NEEDLE. 



Oersted has made an ingenious and novel application of the mag- 

 netic multiplier. He finds that if a good electro-magnetic multiplier 

 with double needles be suspended by a hair or a thread of unspun 

 silk between two pieces of wrought silver, differing only one per cent, 

 in the quantity of copper they contain, so sensible an effect is pro- 

 duced upon the needle as to render this a more accurate method of 

 proof than the common touch-stones. Small trial-plates are made of 

 different degrees of purity, and the piece to be tried is compared with 

 them in the following way : A thin piece of woollen cloth is dipped 

 in muriatic acid, and laid upon the trial-plate, after which the piece 

 to be tried is brought into contact with the acid and the wire of the 

 multiplier. The deviation of the needle shows which contains the 

 most alloy, and another trial-plate must be employed till the needle 

 ceases to be affected, when both are of equal fineness. In coming 

 to a conclusion on this point, however, several circumstances are to 

 be taken into consideration. Wrought silver goods are generally 

 deprived of a portion of their copper by the action of acids, so as to 

 render the surface finer than the inner part of the metal ; the proof- 

 plates, therefore, must be prepared in the same way. Another source 

 of error in the indications of the needle are the unequal polish and 

 size of the two pieces of metal ; the latter of these is especially dif- 

 ficult to overcome when the surface of the metal to be proved is not 

 plain. When, instead of muriatic acid, a dilute solution of caustic 

 potash is employed, and the result is unlike, it is shown that copper 

 is not the only alloy, but that brass is present; and the potash solu- 

 tion renders that which contains brass so positive, that it seems con- 

 siderably purer than the trial-plate. This is the case also in a very 

 high degree when the alloyed metal contains arsenic, for example 

 when what is called white metal has been used for an alloy. This 

 mode of proof is exceedingly interesting in a scientific point of view, 

 and cases may occur in which it can be employed with advantage j 

 but the sources of error can scarcely be ever so completely done away 

 with as to make it a practical instrument in the hands of the silver- 

 smith, as Oersted seems to expect. — Berzelius, Arsberdttelse, 1829, 

 p. 123. — Brewster's Journal. 



ROYAL 



