An account of a useful discovery to distill double the usual quantity of sea-water, by blowing showers of air up through the distilling liquor

by Stephen Hales

26. As it might be suspected, that more Spirit of Salt would be raised, and distilled over in the ventilating Way, than without it; having procured 18 Gallons of Sea-water by the Margate Hoy, which was taken up at some Distance from the Shore, I put three Gallons of this Sea-water, as soon as I had received it, into the Still; and when it began to distill, Air was blown up thro’ it. For some Time, as is usual, in the Distillation of Sea-water; no Spirit of Salt arose; but after distilling some Time longer, there were very weak whitish Clouds, with Drops of Solution of Silver in Aqua-fortis, as in the common Way of distilling. Hence we see, that Ventilation does not increase the Quantity of Salt, but rather probably somewhat decreases it, for the Reasons above given, N^o 24.

27. I distilled three Gallons of Sea-water, which had stunk and became sweet again; when about ten Quarts of it had been distilled off, then there began to be very weak whitish Clouds with Solution of Silver, but none with Solution of Mercury; which shows the Water to be hitherto good, agreeably to what I formerly had found to be the good Effect of distilling Sea-water, which had putrified, and become sweet again; of which I published an Account in the Year 1739. But when I continued the Distillation on, a quarter of an Hour longer, viz. till there was but a Pint of Water remaining in the Still, and the Salts were incrusted on its Sides, up near three Inches from the Bottom, and lay in Heaps at the Bottom of the Still, then the distilled Liquor had whitish Clouds in it, with the Solution of Mercury in Aqua-fortis. From this Distillation we see, that Putrefaction, by dissolving the bittern Salt and Bitumen, into very minute Parts, qualified them to combine with the more fixed common Salt, so as to detain them from rising in Distillation.

28. I distilled three Gallons of Sea-water, with the Proportion of six Ounces of Mr. Appleby’s Lapis Infernalis, and six Ounces of calcined Bones to 20 Gallons of Sea-water, as he directs. This Water lathered well with Soap, and boiled Peas well.

29. I distilled also some Sea-water With half an Ounce of Stone Lime to a Gallon, from the Clee Hills in Herefordshire, which having been preserved ten Months in a Firkin, had slacked to dry Powder. This distilled Water did also lather well with Soap, and boiled Peas well; which proves that the Lime, which is a fixed Body, does not distill over with the Water. Since I made this Distillation, General Oglethorpe informed me, that his Father, Sir Theophilus, told him, that Lime was one of the Ingredients, of what he and the rest of the Patentees, in Charles the Second’s time, called the Cement, with which they made distilled Sea-water wholsome.

30. I distilled also some Sea-water with the like Proportion of powdered Chalk, which boiled Peas well, and was better tasted than the Waters distilled with Lapis Infernalis or Lime. I distilled also some Sea-water with an Ounce of Chalk to a Gallon, but found no Difference in the Taste of this, and that which had but half an Ounce of Chalk to a Gallon: So that half an Ounce of Chalk to a Gallon of Water will be sufficient; but where the Sea-water is salter, or more bituminous, more Chalk may be added if needful.

31. Dr. Alston of Edinburgh, in the Preface to the Second Edition of his Dissertation on Quick-lime and Lime-water, says, that “the like Effect was found in distilling Sea-water with Lime, that it neither precipitated a Solution of Silver in Aqua-fortis, nor a Solution of corrosive Sublimate in Water, nor did it form a Pellicle of various Colours on its Surface, as did the Water distilled by Mr. Appleby’s Process.” And I find, Page 35 of my Book on this Subject, that Lime of Oyster-shells had the same good Effect, but required two Distillations; I might then use too small a Quantity of that Lime. Hence it is probable, that the Chalk, the Lime, the Lime in the Lapis Infernalis, and the Lime in Dr. Butler’s Soap-lees, seize on and fix not only the bittern Salt, but also the Bitumen of the Sea-water, as we learn from the like Effect in the Purification of the Salt of Hartshorn. That the saline Spirit arises chiefly from the bittern Salt, and not from the more perfect Sea-salt, is probable from hence, viz. when I distilled three Gallons of common Water, made as salt as Sea-water with common Salt; no Spirit of Salt arose, even tho’ the Distillation was carried so far as to leave the Salt, tho’ very damp, to lie in Heaps, and it was incrusted on the Sides of the Still, for about three Inches from the Bottom.

32. It is a considerable further Advantage, that Water thus distilled by Ventilation, being thereby repleat and freshened with Air, has for present Use a more agreeable Taste, than Water distilled without Ventilation, which requires the standing a longer Time to have its more disagreeable adust Taste go off. And as the volatile Oil of Pepper-mint does rise on the Wings of the ventilating Air during the Distillation; so also may that Part of the Bitumen, which is volatilized by Heat; as also the volatile urinous Salts of the Sea-water, which arises from animal Substances, be sublimed in the same Manner.

33. It was observable, that the Water distilled fast, even tho’ the Water in the Still was below the Surface of the Tin Air-box, thro’ which the greatest Part of the ascending Shower of Air rushed. Hence the ventilating Air, in ascending among the Vapours, carries them off fast. Hence it is to be suspected, that this Method of Ventilation will not do well for simple Waters, or fermented vinous Spirits; because they being very volatile, much of them may be carried off in Waste.

34. It was observable, that in these Distillations of Sea-water, no whitish Clouds appeared on dropping in Solution of corrosive Mercury, not even when considerably more than four Parts in five of the Water had been distilled over. And it was the same with the Mixture of Lapis Infernalis, Lime, and Chalk; whence it is probable, that the Lime and Chalk seize on and fix the more volatile bittern Salt, as does also the Lime in the Lapis Infernalis. And it is well known, that Sugar, that sweet Salt, cannot be made without Lime, on which, as its Centre of Union, it fixes and granulates.

35. And whereas with a Solution of Silver in Aqua-fortis, which was much weakened and diluted with Water, there appeared a faint Degree of whitish Cloud, in all the above-mentioned Distillations, tho’ not with the stronger Solution of Mercury till the Distillation was carried on, much beyond four Parts in five of the Water in the Still; when both Solutions caused remarkably white Clouds, especially the Solution of Mercury; which indicates the Quantity of the Spirit of Salt which was raised during the former part of the Distillation to be exceeding small, since it could not seize on, nor disengage the Aqua-fortis from the stronger Solution of Mercury, tho’ it did in a very small Degree in the weak Solution of Silver, so as to let loose a very little of the Silver, which thereby caused the faint Clouds. When a Drop of the Solution of Mercury was dropped into the distilled Water, after a Drop of the Solution of Silver, it resorbed the Silver Cloud, and made the Water clear, by means of the great Proportion of acid Aqua-fortis that was in it.