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qualities, shown in its comparative opacity, whilst possessing a real 

 transparency ; its high yellow reflexion and its true green trans- 

 mission ; its known action on light in very minute quantity ; its 

 capability of extreme division ; its great gravitating force, which 

 could be called upon for aid when the metal was in a state of ex- 

 treme division ; its elementary character ; the integrity of its metallic 

 state ; the facilities of testing its presence and condition ; and, 

 finally, because known phenomena seemed already to indicate dif- 

 ferences of action on light consequent upon its division. 



The first state of division or attenuation considered, was that con- 

 ferred on gold by beating into leaves. These, with their dimensions and 

 general characters, are well known. Being taken up on glass damped 

 by breathing or moistening, and then water introduced between the 

 glass and the gold as a cushion, the gold can be perfectly stretched, 

 so that when dry it is fit for optical examination ; or if a diluted solu- 

 tion of cyanide of potassium be in like manner introduced beneath the 

 gold, it can be more or less attenuated by solution, and then washed 

 and dried. If gold-leaf thus extended and attached, either to glass, 

 or plates of rock-crystal, or mica, be heated, it gradually loses its 

 reflective power and its green colour, and becomes translucent. This 

 change takes place far below the fusing-point of gold, and at a 

 temperature as low as the boiling-point of oil if continued for several 

 hours. When the heat is considerable, the gold-leaf suffers retrac- 

 tion of its parts, and becomes perforated by many fine holes, often 

 symmetric in their form and dimension ; but when the heat applied 

 is the lowest competent to produce the change, it does not seem certain 

 that the effect is due to such retraction ; a good microscopic exa- 

 mination of this point is required. When pressure is applied to 

 such decoloured gold by a convex piece of rock-crystal of short 

 radius (as half an inch or less), the green colour of the transmitted 

 ray reappears. This production of the green colour by pressure can 

 often be referred to in different states of gold, as a proof, amongst 

 others, that the metal is in the metallic condition. Silver-leaf 

 undergoes a like change by heat, at even a lower temperature. 



Division by the Leyden Deflagration. When a gold wire is 

 deflagrated near the surface of glass plates by a strong electric dis- 

 charge, it is dissipated in minute particles, which are deposited on 

 the glass. These are seen by the microscope to be of different sizes; 



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