75. In order to bring the Method of procuring Plenty of good Fresh-water at Sea, into practice, several previous Trials were made, at the laudable Motion and Desire of _Peter Wyche_, Esq; in a Still containing 24 Gallons of Water, at Messrs. _Steel_ and _Stephens_’s Copper Workhouse, near the _Falkon-Stairs, Southwark_. The first thing to be done, was to find out the proper Size of the Diameter of the Copper Air-box. The Diameter of the Still, near its Bottom, being 19 Inches, the Diameter of the first Air-box was 18 + ½ Inches. On three several Trials, a _Winchester_ Quart of Water was distilled in five Minutes by the common way of Distillation; and by Ventilation a Quart was, in 3 or 4 Trials, distilled in 2 Minutes; but at the Distillation of the ninth Quart, the Water was so much cooled by the ventilating Showers of ascending Air, as to require 5 Minutes and 44 Seconds. Now this great Decrease of the Quantities distilled, was plainly owing to the too great Breadth of the Air-box, which hindered the Fire from heating and keeping hot the Water which was above it, to such a Degree, as to have no Distillation in the common way, for 8 or 10 Minutes after the Ventilations; for the half Inch Circle of Water which was not covered by the Air-box, was but one nineteenth Part of the whole. The next Trial, in the same Still, was made with an Air-box, whose Diameter was 13 Inches, its Area therefore 127 square Inches; which deducted from 271 square Inches, the whole Area or Breadth of that part of the Still, there remains 144 square Inches, for the Area of the three Inch broad annular Circle round the Air-box, _viz._ 17 square Inches more than the Area of the Air-box. The Event was, that in seven Distillations in the common way, a Quart was distilled in 5 Minutes, sometimes in a little less, and sometimes in a longer Time. And by Ventilation 14 different Quarts were distilled in different Lengths of Time, from a Quart in 2 Minutes and 6 Seconds, to 3 or 4 Minutes. 76. I then repeated the like Trials with my small three Gallon Still, distilling in the common way a Pint in 10 + ½ and 9 Minutes; and seven separate Pints were distilled by Ventilation in 3 + ½ to 4 + ½ Minutes. Hence we see that Ventilation has a more steddy and constant good Effect where the Air-box is less in Proportion to the Still, than it was in the other two Distillations: For in this lesser Still, only 27 out of 99 square Inches were ventilated, 72 square Inches being unventilated. It will therefore probably be advisable to have the Air-boxes of other Stills to be nearly in the like Proportion to the respective Stills, the Diameter of this Still being 11 + ½ Inches, of its Air-box 6 Inches. 77. As by repeated Trials a Quart of Water was distilled in the common way in five Minutes, in the above-mentioned twenty Gallon Still, so an 120, or two Tuns and 14 Gallons, may be distilled by Ventilation in twenty Hours.