_Author_. Truly, sir, this question does a little startle me, because I never expected to meet any water of such a corrosive quality in any mine: and could I find out a mine, whose water abounds with such acid particles, as to destroy or injure the copper vessels of my engine, I would drain that mine for nothing but the water I shall take up; because the water would be more valuable than any ore (I believe) in England. And were there even a tenth part of aquafortis to nine-tenths of common water, which is impossible to suppose it should be, I say, such a water could have no effect on the coppers, were that water to lodge some time in the copper vessels, much less in passing through them with that celerity and rapid motion that always accompanies it. _Miner_. But, sir, will not such a continual fire, as must be kept under your boilers, burn them out in two or three months’ time, and spoil the work of your engine? _Author_. I can assure you they will not decay in some years, unless some fellow be hired or employed on purpose to do it. And should any villain be employed to burn, break, or destroy any of the engines now used in your works for raising of water, we are then on the same level with you in that point. But I will give you one reason why my engines will not easily decay, and I am sure that will go further with you than all the affirmation I can make. For, first of all, although a white heat will melt copper, and a red heat, and sudden cooling it again, will scale the copper, yet such a heat as is possible for it to have or suffer while water is in the boiler can have no ill effect, or cause any alteration in our copper. A friend of mine has coppers used in sugar boiling of twenty years’ standing. They may be a small matter worn with cleaning on the inside, whereas on the outside there does not appear the least visible decay: for as soon as the fire has thrown a thin coat of soot on the outside of the boiler, the flame has no other effect on it than to cause the water in it to boil. _Miner_. But we have often combustible vapours in our mines, which taking fire from the candles used there, do, by a sudden explosion, destroy both the mine and the miner; and therefore I am afraid that the fire used in your engine will be very dangerous, and apt to kindle those combustibles more than our candles.