VOL. XHX.] PHILOSOPHICAL TRANSACTIONS. 637 



taken oft". For, according to the different depths of the liquor in the still, so 

 will the force of the included air, against the upper board of the bellows, be more 

 or less. Wherever the stills are tixed in ships, the air may be conveyed to them 

 from the bellows, either through a small leathern pipe, distended with spiral coils 

 of wire, or through Bamboo canes, or broad small wooden pipes, like hollow 

 fishing rods. In several distillations of a quart at a time. Dr. H. found the 

 quantity distilled by ventilation to be more than the double of that in the usual 

 way. So that the quantity by ventilation may, at a medium, be estimated the 

 double of the usual distillation. It is the well-known property of moving air, to 

 carry along with it a considerable quantity of adjoining vapour, as also of falling 

 water to carry much air down along with it. ■ It is to be hoped therefore, that so 

 considerable an increase in the quantity distilled will be of great benefit to navi- 

 gation, as it may be done in less time, and with less fire. 



In the account of Mr. Appleby's process, for making sea-water fresh, pub- . 

 lished 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 distil 6o gallons in 

 10 hours, with little more than one bushel of coals ; and therefore 120 gallons 

 in 20 hours, with little more than 2 bushels of coals. And by ventilation 240 

 gallons, or a tun ; and 24 gallons may be distilled in 20 hours, making an al- 

 lowance for the times of heating those stills full of cold water; and still a larger 

 and wider will distil a tun in 24 hours ; which will more than suffice for a sixty 

 gun ship, with 400 men, whose provision of water for 4 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. 



There are holes in the feet of the iron frame or stove of these stills, to screw 

 them down to the deck. They were fixed at the fore-castle before the mast, in 

 King Charles the 2d's time, when they thought they had discovered the way to 

 distil sea-water, free from the noxious spirit of salt, and from the nauseous bitter 

 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. 



Doctor Butler, in his lately published method of procuring fresh water at sea, 

 proposes the pouring in more sea-water into the still, through 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 dis- 

 tilling 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 to increase the quantity of water 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 from over the hole. Doctor Butler used capital 

 6oap-lees, in the proportion of a wine quart to 15 gallons of sea-water; which 



