212 Analyses of Books. [Sept 



Exper. 20. A colourless Fluid, which acquires a blue Colour 

 when the. Bottle containing it is opened, and which becomes limpid 

 again when the Bottle is closed. — Put into an ounce phial a 

 slip of copper, previously scraped bright : fill up the phial with 

 liquid ammonia, and cork it air-tight. No apparent change will 

 take place ; but if the bottle be left open for some hours, and 

 then be closed, a solution of the colour is effected, which is abso- 

 lutely colourless, but turns blue on re-opening the bottle, begin- 

 ning at the surface, and gradually extending downwards through 

 the mass. Again, if this blue solution has not been too long 

 exposed to the air, and fresh pieces of copper be put in, stopping 

 the bottle again, the solution is deprived of all its tinge, and 

 recovers its colour only by the admission of the air. And this 

 effect may be produced repeatedly. 



Rationale. — Metallic copper is not acted upon by liquid 

 ammonia, but is soluble in this fluid when oxidated. This oxida- 

 tion is effected by the influence of oxygen when atmospheric air 

 is admitted. Hence, when the copper is no further oxidated 

 than is necessary for solution, the compound is colourless ; but 

 it acquires a blue colour when the metal is oxidated in a higher 

 degree. It is also obvious, that this azure colour is again 

 destroyed by the addition of more copper filings, and exclusion 

 of air, as the newly added metal deprives that which was con- 

 tained in the solution in an oxidated state, of its superabundance 

 of oxygen, in order to be dissolved also in the liquid. The solu- 

 tion of copper in ammonia, at a minimum of oxidation, is, there- 

 fore, colourless ; but if the metal be highly oxidated, the solution 

 has a blue colour. 



Exper. 21. To prove that Water is contained in the Air of the 

 Atmosphere, even during the driest Weather. — Take a tea-spoonful 

 of dry muriate of lime, acetate of potash, or sub-carbonate of 

 potash, put it into a saucer or other vessel, and suffer it to be 

 exposed to the open air for a few days. The dry salt will thus 

 be rendered completely liquid by the watery vapour which always 

 exists in the atmosphere. 



The proportion of watery vapour existing in the atmosphere 

 varies considerably, principally according to temperature. While 

 the water preserves the aerial form, the air containing it is 

 perfectly transparent ; even in this state, however, it can be 

 discovered existing in it ; but when the vapour is condensing, it 

 communicates to the air a degree of opacity from the conglome- 

 ration of the particles of water. This, according to the extent 

 to which it happens, gives rise to the natural appearances of 

 clouds, mist, and rain. 



Exper. 22. To write luminous Characters. — Write with a stick 

 of phosphorus on a board, or on any rough surface : the charac- 

 ters will be luminous in the dark, as if on fire, and continue so 

 ior some time. The luminous appearance vanishes by blowing 

 on the writing, and becomes visible again instantly. 

 If letters be written on a dark-coloured paper, and the writing 



