and for slalnrng and gilding Glass. 265 



reel hot into cold water; after having thus treated them two or 

 three times, pulverize them in a biscuit-ware mortar with a pestle 

 of the same, (which will be easily effected,) and then grind them 

 in water on plate glass. 



Where no opportunity occurs of procuring burnt flints from 

 the lime burners, the common black flints broken into pieces, 

 made hot in boiling water (to prevent their flying in the crucible,) 

 and treated in the same way, will produce a fine white powder. 



Red Sulphate of Iron. 

 Sulphate of iron, otherwise called green vitriol, is t« be pounded 

 and placed in an earthen ware muffle, (which may be had at the 

 ironmongers, in Foster-lane; or at Mr. Accum's, in Comptou- 

 street) till the moisture is evaporated and a gray powder left ; 

 which place in a crucible in a charcoal fire, and stir it with a 

 piece of steel bar, till it is of a fine red colour ; then let it fall 

 out of the crucible into a pan of cold water, under a chimney, 

 to avoid the disagreeable fumes that arise ; when settled at the 

 bottom wash it in several hot waters, and then dry it for use. 

 The more it is burnt, the darker the red. 



Broun Siilj)hate of Iron. 

 Take sulphate of iron in lumps, and calcine it in a red char- 

 coal heat till it becomes of a dark brown; and let it cool in the 

 crucible, afterwards wash it repeatedly in hot water. 



Black Oxide of Copper. 

 Take copper and dissolve it in aquafortis, till the acid refuses 

 to take up any more metal ; then dilute the solution with water, 

 and add to it some subcarbonate of potash, dissolved in water; 

 a green precipitate will fall to the bottom, which must be washed 

 in several hot waters ; when settled, pour off the superfluous 

 water, and place the green matter at the bottom on a piece of 

 coarse open canvass, tied over a large earthen pan, on which a 

 piece of blotting paper is laid ; after the precipitate has been 

 thus drained, it should be taken off and made perfectly dry, by 

 placing the paper on a drawer of powdered chalk to absorb more 

 of the moisture, and then placed before the fire. When dry, 

 calcine it in a crucible in a charcoal fire, and throw it red hot 

 into cold water ; then rinse it in boiling water, and dry at the 

 bottom of the bason before a fire ; what remains is a beautiful 

 black oxide of copper. 



Green Oxide of Copper. 

 Take a saturated solution of copper in aquafortis, and preci- 

 pitate it with subcarbonate of potash ; then wash it several times 

 ju boiling water, filter and dry it, 



Wkite 



