ESSAY XIV. 



METHOD OF PREPARING A NEW GREEN COLOUR. 1778. 



CHEMISTRY is well known to be indispensably necessary in 

 the preparation of colours for painting, and it often discovers 

 new ones. It was the desire of the Koyal Academy that 

 the green colour which I observed during my experiments 

 on arsenic might be made more generally known, together 

 with the mode of preparation. In compliance with this 

 desire, I give the present account of it, and that with the 

 greater pleasure, as I have found the colour useful both in 

 oil and water painting, and as it has not undergone the 

 slightest alteration in the course of three years. 



Dissolve 2 Ib. of vitriol over the fire in a copper vessel, 

 in six cans of pure water, and as soon as it is dissolved 

 take the kettle from the fire. 



Then dissolve in another copper kettle 2 Ib. of dry 

 white potashes and 11 oz. of pounded white arsenic, 1 

 in two cans of pure water over the fire. When all is 

 dissolved together, strain it through linen into another 

 vessel. 



Of this arsenical ley a little is to be poured at a tim.e 

 into the above-mentioned solution of vitriol of copper, while 



1 It is always better to pound the arsenic one's self than to buy it 

 ready pounded ; for this is often adulterated with gypsum, of which 

 any one may readily convince himself by laying a little with the point 

 of a knife upon a red hot coal. If the whole evaporate without leaving 

 any residuum, the arsenic is pure. 



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