1 23 ) 
nearly emptied, the glafs remaining’ at the bottom’ 
is always blue } this is caufed by it’s continuing 
longed; expofed to the fire, and in fo fmall a quan- 
tity that the fire has a greater efFedt on it. The 
whole mafs acquires the fame colour ^ if too much 
fand be added in proportion to the afhes ; for, in 
that cafe, the materials being more difficult of 
fufion, the workmen are obliged to ripply a greater 
heat, and to continue it longer. 
It is known, from the experiments of Leinery 
and others, that the vegetable afhes contain iron [at]. 
To examine whether that metal be alfo contained 
in the fand ufed in making this glafs, and how far 
the colour of the glafs depends upon it, I made the 
following experiments : 
Exp. I. Having procured fome of the fand ufed 
in making green glafs, I melted two parts of it 
with one part of borax, and one part of nitre, and 
found that it produced a glafs fimilar in colour to 
that which is made with the fame fand fluxed with 
pot afhes. Froni hence it appears, that the colour- 
ing matter was contained in the fand. 
Exp. 2. I mixed- three parts of this fand with- 
one of powder’d charcoal, and expofed it for fome 
[x] Becher, Phyf. Subterran. p, 67. 
Hsec prima terra (vegetabilis) cum mlneralibus vitris, quae ex 
arena et I'llicibus parantur, conveniens eft, ut nulla re, nifi colore,, 
inde difcerni queat, qui viridis eft, vel fuhcoeridcus^ indelebilcni 
regni fui afterileum lervans, nempe 'vegetahilem v'iriditatc7n ex- 
primens. 
Flora Sat. cap. 8. Note 
As that blue or green colour is owing to the iron which is 
found in the afhes ot all vegetables, it muft not be lo.jked on as 
a mark capable of charadterifing a vegetable earth. 
hours 
