6. It is to be hoped therefore, that so considerable an Increase in the Quantity distilled, will be of great Benefit to Navigation, as it may be done in less Time and with less Fire.
7. In the Account of Mr. Appleby’s Process, for making Sea-water fresh, which is published by Order of the Lords of the Admiralty in the Gazette of Jan. 22, 1754, it is said that a Still which contains 20 Gallons of Water will distill 60 Gallons in ten Hours with little more than one Bushel of Coals; and therefore 120 Gallons in 20 Hours, with little more than two Bushels of Coals. And by Ventilation 240 Gallons, or a Tun; and 24 Gallons may be distilled in twenty Hours, making an Allowance for the times of heating those Stills full of cold Water; and a Still something larger and wider, will distill a Tun in 24 Hours; which will more than suffice for a sixty Gun Ship with 400 Men, whose Provision of Water for four Months is about 110 Tuns. And larger Ships may either have proportionably larger Stills, or else two of them. As for Merchant-Ships with few Men, a small Still will be sufficient.
8. The second sized Stills contain 10 Gallons, and will produce 60 Gallons in 20 Hours, with half the above-mentioned Fuel; and by Ventilation 120 Gallons.
9. The least Stills contain five Gallons, and will produce 32 Gallons in 20 Hours; and by Ventilation 64 Gallons in 20 Hours.
10. I have seen some of these Stills at Messrs. Steel and Stephens, over-against Mercers-Chapel, in Cheapside, which have been made for this Purpose. There are Holes in the Feet of the Iron Frame or Stove to skrew them down to the Deck. They were fixed at the Fore-castle before the Mast in King Charles the Second’s time, when they thought they had discovered the Way to distill Sea-water, free from the noxious Spirit of Salt, and from the nauseous bittern Taste. Or, if it be thought proper, one Part of the Ship’s Boiler may be made use of, by adapting a Still-head to it.
11. Now supposing a Still to contain 25 Gallons, and that four Parts in five of it, viz. 20 Gallons are distilled off: then, in order to distill a Tun, or 210 Gallons, the Still must be emptied, cleansed and refilled eleven times; and if the whole be done in 24 Hours, full 16 of those Hours will be taken up in distilling at the rate of a Gallon in about four Minutes and half; and the remaining eight Hours of the 24, being divided into 11 equal Parts, they will be each near 44 Minutes to empty and cleanse the Still, to refill it, and give the Sea-water a proper boiling distilling Heat: whether this can be done in so short a Time, must be known by Experience, and ought therefore first to be tried at Land.
12. Doctor Butler, in his lately published Method of procuring Fresh Water at Sea, proposes the pouring in more Sea-water into the Still, thro’ a Funnel fixed in a small Hole in the Head or Upper-part of the Still, when more than half the former Water is distilled off; by which means the Water in the Still will soon acquire a distilling Heat; and this to be repeated several times; but then it will be requisite to add each time more Chalk, in such Proportion as shall be found requisite. It will be well to try this Method in hopes thereby to increase the Quantity of Water that is distilled. The Hole in the Head, or Upper-part of the Still, is to be stopped with a small Plate of Copper, so fixed as to turn to and fro over the Hole.
13. Doctor Butler used capital Soap Lees, in the Proportion of a Wine Quart to 15 Gallons of Sea-water, which sufficed for four or five times repeated Pourings in of more Sea-water into the Still. But as I have found that a small Quantity of Chalk has the same good Effect, and is cheaper, and more easily to be had, it is therefore preferable to Soap Lees.
14. When there is a Fire in the Cook-room, the Sea-water might be ready heated to put into the Still, without any additional Expence of Fuel, in the following Manner, which I shall here describe; tho’ I think it probable that it will not be put in practice; yet, as farther Improvements may possibly hereafter be made in it, and as it may be of use in some Cases, at Land at least, I shall here give an Account of it, viz.
15. About the Year 1718, Mr. Schmetou a German Gentleman, got a Patent here for heating great Quantities of Water, with little Expence of Fuel, which he then shewed me. Having fixed a spiral Iron Worm-pipe, in such a Brick Stove or Chimney as Women heat their Irons in, thereby causing the Water to run from a Vessel, thro’ the Worm-pipe, several Feet Length round, in the Fire. About 30 Years after I acquainted Mr. Cramond of Twickenham with this, as hoping it might be of Benefit in distilling Sea-water. Upon which he procured such a spiral Iron Worm-pipe, which was about twenty Feet long, and six-tenths Inch Diameter; the Diameter of the spiral Coile was about fourteen Inches.