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Solutions of iron, and of its ores, In the marine and 
nitrous acids, as alfo pyrites diffolved in rain-water, 
were fubflituted, by turns, inftead of the original iron 
iii vitriolic acid ; and they all gave a purple colour 
with tindure of galls. 
The trials were repeated with lime-ftone, marble, 
hland cryftal, ofteocolla, and magnefia, in lieu of 
chalk j and with volatile and mineral alcali, replete 
with air, in the room of fait of tartar j but no mate- 
rial difference was obferved. 
The fuccefs of thefe experiments compleatly an- 
fvvered my expedations. They fatisfied me, that any 
acid holding iron diffolved, and diluted with water, 
might not only be neutralized, but the water charged 
with an excefs of alcaline or earthy matter, without 
precipitating the metal ; and that the folvent, in thefe 
cafes, could be no other than Fixed Air. Since the 
iron remained in folution, only where this principle 
originally abounded in the water, or was afterwards^ 
generated in the faturation. 
Thus much being determined, it feemed ealy to, 
apply the difeovery to the more perfed analyzation of 
fome waters 5 and to the re-produdion of others, by. 
art, which fhould exadly refemble thofe o-f natural 
medicated fprings. This is a talk I fliould probably 
have undertaken at leifure ; had I not been informed, 
that Dr. W'atfon, junior, by whofe converfition my 
thoughts were firft led to the fubjed, is already en- 
gaged in fomething of this fort. This gentleman 
law many of the foregoing experiments repeated ; and; 
as he is fmee gone to the Germaji Spa, I dare fay, his 
'ibilities. and ajiplication will fuffiiciently improve 
