356 ANALYSIS of a BLACK SAND 
6. WHEN evaporated to drynefs, and rediffolved in water, a 
white powder remained, which proved to be filica, and which, 
after being heated to rednefs, weighed one grain. 
4. THE watery folution being fuperfaturated with potafh, 
and boiled for a few minutes, was thrown upon a filter, to fe- 
parate a reddifh-brown matter, which had been precipitated. 
The clear liquid which paffed through the filter, was mixed 
with a folution of fal ammoniac. A foft white matter flowly 
fubfided. It was alumina, and, after being heated to rednefs, 
weighed half a grain. 
8. Tue brown-coloured matter which had been precipitated 
by the potafh, when dried upon the fteam-bath, weighed 20.2 
grains. It diflolved with effervefcence in muriatic acid. The 
folution had the appearance of the yolk of an egg, When 
boiled for fome time, and then diluted with water, it became 
white, and let fall a curdy precipitate, which weighed, when 
dry, 4.6 grains, and poflefled the properties of oxide of tita- 
nium. ; 
g. THE refidual liquor being mixed with an excefs of ammo- 
nia, let falla brown matter, which, after being dried, drench- 
ed in oil, and heated to rednefs, weighed 6 grains.  It-was 
flrongly attracted by the magnet, but was of too light a colour 
to be pure oxide of iron. I therefore: diffolved it in muriatic 
acid, and placed it on the fand-bath, in a porcelain capfule. 
When very much concentrated by evaporation, fmall white” 
needles began to make their appearance in it.) The addition of 
hot-water made them difappear; but they were again form- 
ed when the liquor became fufficiently concentrated. Thefe 
cryftals, when feparated, weighed 1.3 grains, and proved, on 
examination, to be white oxide of arfenic. During the folution 
of 
