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portion as they are combined with
thority of Hoffman, and the opinion of many concerning the refidence of the nitrous acid in the air, that it is not to be found therein; and this I am the better authorised to deliver, as I never could procure, after proper trials, any ves. tiges of nitre from hail, snow, rain-water, or dew. These experiments terminating wholly fruitless, I determined to go back to the place where I once intended to set off from; if the accounts I had met with in authors had not flattered me with hopes of a more speedy mode of acquisition. The decomposition of nitre was now un
talled, between the two parties, and is always found to give way to superior influence, viz. to a greater affinity between ore of the parties, and some substance added, than does subsist between the parties first united; this is the cause of every kind of chemical precipitation. Gold dissolved in aqua regia is precipitated by adoing copper to the solution; the copper in the same manner gives way to iron, and iron to an earth or vegetable alcali. In the same manner, and by the same law, all waters that are impregnated either with the marine, the vitriolic, or the nitrous acid, and which have their acid saturated or neutralised by any kind of mineral they have met with in their passage or residence under ground, will be obliged to part with that mineral by adding to them any kind of vegetable alcali; and this by the greater affinity there is between their acid and a vegetable alcali, than between their acid and any kind of earth or metal whatever.