Elements of the Theory and Practice of Chymistry, 5th ed.

by Pierre Joseph Macquer

A Spirit of Salt that shall not smoke may also be obtained by means of the pure Vitriolic Acid. Spirit of Vitriol, or Oil of Vitriol, lowered with a good deal of water, will do the business.

Some Chymists direct a little water to be placed in the receiver, when Spirit of Salt is to be distilled by the intermedium of concentrated Oil of Vitriol, in order to make the acid vapours condense more readily. By this means indeed some of the inconveniencies attending the distillation of smoking Spirit of Salt may be avoided: but, on the other hand, the acid vapours being absolutely suffocated by the water as fast as they come over, the Spirit of Salt obtained by this method will be no less aqueous than that procured by the interposition of earths: so that here is an expence to no manner of purpose. Therefore, when a Spirit of Salt is desired that shall not smoke, it is best to employ an additament of earth; and that so much the rather as the Marine Acid obtained by this means is purer and freer from any Vitriolic taint, for the reasons already assigned.

Part of the Acid of Sea-salt may be separated from its Alkaline basis by the force of fire alone, without the intervention of any other body. With this view the Salt must be put into the retort without being dried. At first an insipid water rises; but it gradually becomes acid, and hath all the properties of Spirit of Salt. When the Salt in the retort is grown perfectly dry, nothing more can be forced over by any degree of heat whatever. If you would obtain more Acid from the same Salt, you must take it out of the retort, where you will find it in a lump, reduce it to powder, and expose it to the air for some time, that it may attract the moisture thereof; or else wet it at once with some rain water, and distil as before. You will again have an insipid water, and a little Spirit of Salt; which will in like manner cease to rise when the Salt in the retort becomes dry. This operation may be repeated as often as shall be thought proper: and perhaps it may be possible to decompose Sea-salt entirely by means thereof, without the interposition of any other body. The Spirit of Salt thus obtained is exceeding weak, in small quantity, and loaded with much water.

This experiment proves, that moisture greatly facilitates the separation of the Acid of Sea-salt from the matters with which it is united: and this is the reason that, in distilling Spirit of Salt with the additament of an earth, the operation requires much less fire at the beginning, while the earth and salt retain a great deal of humidity, than towards the end, when they begin to grow dry.

After the operation there remains in the retort a saline and earthy mass, which contains, 1. Some entire Sea-salt that has suffered no decomposition; 2. A Glauber's Salt which is, as we said before, a Neutral Salt consisting of the Vitriolic Acid united with the Alkaline basis of the Sea-salt, from which it hath expelled its proper Acid; 3. Part of the earth used as an intermedium, still retaining a portion of its original Vitriolic Acid, which happening not to lie near enough to any particles of Sea-salt, could not exert its power in decomposing them, and so remains united with its earthy basis; 4. Another part of the same earth, impregnated with some of the Marine Acid, which combined therewith upon being expelled from its Alkaline basis by the Vitriolic Acid, and which the force of fire was unable to separate from it when the matters were grown perfectly dry. In consequence of what remains in this caput mortuum, if the whole mass be triturated, moistened with a little water, and distilled a second time, considerably more Spirit of Salt will be obtained from it: and the same is to be said of all distillations of this sort.

Spirit of Salt obtained by the means of any other additament than concentrated Oil of Vitriol is generally very weak: but it may be dephlegmated and concentrated, if required, much in the same manner as Oil of Vitriol. For this purpose you must put it into a glass cucurbit, set it in a balneum mariæ, fit thereto a head and a receiver, and with a moderate degree of heat draw off one third or one half of the liquor. What comes over into the receiver will be the most aqueous part, which being the lightest will rise first, impregnated however with a little acid: in the cucurbit will be left a concentrated Spirit of Salt, or the most acid part, which being the heaviest will not rise with the degree of heat that is capable of carrying up the phlegm. Spirit of Salt thus concentrated, called also Oil of Salt, does not smoke: it is of a yellow colour inclining to green, and an agreeable smell, not unlike that of saffron.

PROCESS IV.

To decompose Sea-salt by means of the Nitrous Acid. Aqua regis. Quadrangular Nitre.

Take dried Sea-salt; bruise it to powder; put it into a glass retort, leaving one half of the vessel empty. Pour upon it a third of its weight of good Spirit of Nitre. Place your retort in the sand-bath of a reverberating furnace; put on the dome; lute to the retort a receiver having a small hole in it, and heat the vessels very slowly. There will come over into the receiver some vapours, and an acid liquor. Increase the fire gradually till nothing more rises. Then unlute the vessels, and pour the liquor out of the receiver into a crystal bottle, stopped like others containing Acid Spirits.