C H7 ] 
Having taken fome pieces of this rock, which 
were quite free from the faline effervefcence; and in- 
fufed them in common fpring-water for fome hours, 
this water did thereby acquire the true tade of the 
Hartfell-Spaw. It likewife in the fame fnanner re- 
ceived a deep blue tin&ure with galls, and con- 
tained all the other qualities of that mineral water, 
without the lead; difference, that I could obferve : 
which, I think, afcertains the true origin of this 
mineral fpring in the mod; obvious and undeniable 
manner. 
I am perfuaded, that this plain and eafy method 
of invedigating the origin of mineral fprings is not 
only fuperior to the mod learned difcuffions and 
elaborate theories, but will be found to be the fured, 
yea, the only Way of extending and compleating our 
knowlege concerning them. As I have not yet had 
the opportunity of making the experiments, which 
I defigned) upon the two foffils, that we find to be 
the caufe of the above mineral waters, and which 
will be neceffary to elucidate and compleat thefe 
obfervations, which we have made concerning their 
origin ; I diall now only add one thing, and recorm 
mend it to the obfervation of others: “ Whether or 
‘ c not , from fuch a knowlege of the origifi of mineral 
u waters , we may not acquire artificial ones of as 
“ great , or perhaps of greater , medicinal ufe y than 
<c thofe , which are naturally produced ? ” 
U 2 
XVIII. 
