132 DR. J. p. JOULE ON SOME AMALGAMS. 



The mean composition of the amalgam, after being 

 pressed with 72 tons on the inch, was therefore 43*71 silver 

 to 100 mercury. Allowing for mercury remaining among 

 the crystals in an uncombined state, we inay conclude 

 that the solid amalgam containing the largest quantity of 

 mercury is composed of one equivalent of silver to two of 

 mercury. 



Amalgam of Platinum. — To obtain this amalgam, pla- 

 tinum was deposited on mercury by the electrolytic action 

 of two or three voltaic cells on the bichloride. 



No. 



Mercory. 



Platinum. 



Sp. grav. 



Remarks. 



I. 



2. 

 3- 



100 



15-48 



21'6 



3476 



14-29 

 14-60 



Metallic lustre when rubbed. 

 Solid. Dark grey colour. 

 Dark grey; no metallic lustre. 



An amalgam of 12 platinum to 100 mercury possesses a 

 bright metallic lustre, and is soft and greasy to the touch. 

 Pressed with a force of 72 tons to the square inch, a hard 

 button of dark grey amalgam is left, consisting of 43*2 parts 

 of platinum to 100 of mercury. I infer therefore that the 

 solid amalgam of platinum, which contains the largest 

 quantity of mercury, is composed of two equivalents of 

 mercury to one of platinum ^. 



The specific gravity of this amalgam appears to be 

 nearly that which it would be on the supposition that 

 no condensation of volume takes place on the union of the 

 metals; but the specimens were too small to make very 

 accurate determinations of specific gra^dty. 



Amalgam of Zinc was obtained electrolytically from sul- 

 phate of zinc ; after some time the mercury lost its fluidity, 

 and branching crystals began to be formed, 



* Amalgam of platinum in the form of a thick paste may be obtained by 

 exposing mercury to the action of bichloride of platinum for a sufEcient 

 length of time. 



