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PHYSICAL anv LITERARY. 357 
_ I diffolved, in a chopin of fourftain-water, 
vitriol. Mart. gr. xv. and in every refpect 
treated it asl had done the Harzfell Spaw 
water, viz. it was evaporated over the fire, 
till there remained about two ounces; this 
was filtrated, and exhaled, in a wide glafs, 
before the fire: there was left inthe glafs gr. 
xifs of a light-yellowifh coloured falt, and in 
the filter a dark-brown earth. With this 
falt, I repeated all the experiments I had 
made with the falt of the Hartfell Spaw; and 
I had the pleafure to fee, that they corre- 
{ponded in every thing, without any material 
difference ; only the falt left upon evaporation 
of vitriolum Martis, did not rife in a blifter 
on the hot iron, and, when diffolved in water, 
gave, with powder of galls, a redifh tin@ure 
inclining to purple: whereas the falt of the 
Harifell Spaw, being diffolved in water, with 
galls, ftruck a blue. The reafon of which 
I take to be, that there is a greater propor- 
tion of acid, in the compofition of the falt of 
the Hartfell Spaw, then there is in the vitrio- 
lum Martis ; for, if you add an alkali,’ as o/, 
_tartart, to the blue tin@ure, produced by 
the falt of Hartfell Spaw, it changes to a red- 
ifh; and if an acid, as o/. vitrioli, is added 
to 
