238 



mon methods for assaying or purifying gold by aqua, 

 fortis, aquaregia, or the regal cement, can no longer 

 be depended on : that it differs from gold, in giving 

 no stain to the solid parts of animals, hot striking a 

 purple colour with tin, not being revived from its so. 

 lutions by inflammable spirits, not being totally preci- 

 pitable by alkaline salts ; that in certain circumstances 

 it throws out gold from its solutions ; that these pro- 

 perties afford means of distinguishing a small portion 

 of gold mixed with a large one of plafina, or a small 

 portion of platina \vith a large one of gold ; and 

 that platina contains no gold excepting the few 

 particles distinguished by the eye. That platina is. 

 precipitated from its solutions by the vitriolic acid, 

 and by the metallic substances, which precipitate gold, 

 though scarce totally by any : and that its precipitates 

 resist vitrification, and this perhaps in a more perfect 

 manner than precipitates of gold itself. It is there- 

 fore a simple metal of a particular kind, essentially 

 distinct from all those hitherto known, though posses- 

 sed of some properties generally supposed peculiar to 

 gold. Many of its characters have been already 

 pointed out; others result from combining it with the 

 several metals, with each of which, notwithstanding 

 its resistance to the most intense fires by itself, or 

 with unmetallic additions, it melts perfectly ; occa- 

 sioning remarkable alterations in their colours, tex- 

 ture, and hardness. It melts with equal its weight 

 of each of the metals, with one more readily than 

 with another. With some it becomes fluid, in a mo- 

 derate fire ; but a strong one is requisite for its per- 

 fect solution. Compositions of silver, copper, lead, 

 with about one third their weight of platina ? which 

 had flowed thin enough to run freely in the mould, 

 and appeared to the eye perfectly mixed, on 

 being digested in aquafortis till the menstruum 

 ceased to act, left several grains of platina in their 

 original form. Upon viewing these with a microscope 

 some appeared to suffer no alteration ; others exhi- 

 bitgd an infinite number of minute, bright, globular 



