Ij56 METALLIC COATING 



It is a material object, and the particular desire of tile 

 academy, that every information which can be gained respect- 

 ing the specimens presented, should accompany them", as 

 regards the climate, soil, locality, and other peculiarities. 



The government of the United States having withdrawn 

 all restrictions on the importation, of objects of Natural His- 

 tory, there will be no difficulty at the custom-house. 



ARTICLE XI. 



On the Metallic Coating- for Electric rubbers. By William 



R. Fisher. 



[Read before the Academy, March, 1836.] 



There are two compounds generally employed for this pur- 

 pose, the bisulphuret of tin (commonly called mosaic gold) and 

 an alloy of tin, zinc and mercury, (known as amalgam.) The 

 former when it can be obtained, is generally preferred on 

 account of its laminated structure; being unctuous, soft and 

 adhesive, but the preparation of it being attended with diffi- 

 culties, and its higher price, have induced many persons to 

 employ the latter, which is much cheaper and more readily 

 made. I shall endeavour, however, to describe the process by 

 •which the former is procured, so that its successful manufac- 

 ture may be pretty confidently relied upon. It^is made by 

 mixing two parts per oxide of tin, two parts of sulphur, and 

 one part muriate of ammonia, all finely powdered until they 

 are thoroughly diffused through each other. This mixture is 

 then put into a Florence flask, which is buried in sand, in a 

 Hessian crucible, up to the neck — the crucible is then exposed 

 to a red heat for several hours, until the full reaction of the 

 materials has taken place, and the bisulphuret of tin is formed ; 

 this may be known by introducing an iron rod into the flask, 

 frequently during the operation, and noticing the appearances 

 indicated upon it, when withdrawn. Until the sulphuret is 

 formed, the rod when withdrawn, is merely covered with 

 sublimed sulphur, but so soon as the mosaic gold begins to 

 form, the rod is found beautifully spangled with crystals of a 

 bright golden colour, and as the formation proceeds, the crys- 



