414 Observations on

Prussian blue. A quantity of lime water,thus impregnated with the colouring mat-ter in Prussian blue, I put into one of myglass tubes on the nth of August, and onthe 23d, from being quite colourless, itwas become of a greenissi colour, withmany opake particles in it. On the 9th ofSeptember following it was quite transpa-rent, with a large white sediment, in whichit resembled the tubes that had only waterin them. This sediment, therefore, mightperhaps come from the corrosion of theglass. On the 30th of September, theliquor was quite cloudy, had a considerableprecipitate, and a thick whitissi incrustationcovered all the surface of it. Lastly, on the19th of January 1778, it had something ofa milky appearance, but was nearly transpa-rent, and had deposited a quantity of flakymatter.

Having the solution of mercury , and alsoof copper in spirit of nitre at hand, propertubes to spare, and room enough for themin my hot sand, I placed about an ouncemeasure of each of them in the furnace on

the

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