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

by Pierre Joseph Macquer

It must be observed, that, on this occasion, the point of saturation is very difficult to hit; owing probably to the Volatility of the Alkali, which, being much lighter than the Acid, tends always to possess the uppermost part of the mixture, while the Acid sinks to the bottom: whence it comes to pass, that the lower part of the liquor is sometimes over-charged with Acid, while the upper part is still very Alkaline. But it is most eligible that the Alkali should predominate in the mixture; because the excess of this principle easily flies off, while the moisture is evaporating, in order to the crystallization or sublimation of the Ammoniacal Salt; which being only semi-volatile resists the heat longer, and remains perfectly Neutral.

If the Vitriolic Acid be combined with a Volatile Alkali, and the mixture distilled in a retort to draw off the superfluous moisture, a liquor comes over into the receiver, which smells strong of a Sulphureous Acid. Now, as the Acid of Vitriol never becomes sulphureous, but when it is combined with an inflammable matter, this experiment is one of those which demonstrate that Volatile Alkalis contain a very sensible quantity of inflammable matter. This same liquor tastes of an Ammoniacal Salt; which proves that it carries up with it some of the Neutral Salt contained in the mixture. The rest of this Salt, which is called Glauber's Secret Sal Ammoniac, or Vitriolic Sal Ammoniac, sublimes into the neck of the retort. It is very pungent on the tongue; it crackles a little when thrown on a red hot shovel, and then flies off in vapours.

The Ammoniacal Salt formed by the Acid of Nitre exhibits much the same phenomena; but it requires greater care in drying and subliming it, because it hath the property of detonating all alone, without the addition of any other inflammable matter: and it will infallibly do so, if too strong a fire be applied towards the end of the operation, when it begins to be very dry. This property of detonating by itself it derives from the inflammable matter contained in the Volatile Alkali which serves for its basis: and this is another demonstrative proof of the existence of such an inflammable matter in the Volatile Alkali. This Salt is called Nitrous Sal Ammoniac.

With the vegetable Acids, that of Vinegar for instance, is formed an Ammoniacal Salt of a singular nature, and which can scarce be brought to a dry form.

A Volatile Alkali, combined to the point of saturation with the Acid of Sea-salt, forms another Neutral Salt, which takes a concrete form either by sublimation or crystallization. The crystals of this Salt are so very soft and fine, that a parcel of it looks like cotton or wool. This is the Salt properly called Sal Ammoniac. It is of great use in Chymistry and in manufactures: but that which is daily consumed in great quantities is not made in the manner above mentioned. It would come extremely dear if we had no other way of procuring it, but by forming it thus with the Acid of Sea-salt and a Volatile Alkali. This Salt, or at least the materials of which it is formed, may be found in the fuliginosities and soots of most animal, and of some vegetable substances. The greatest part of what we use comes from Egypt, where vast quantities thereof are made.

The method of preparing Sal Ammoniac in Egypt was not known among us, till Mess. Lemaire and Granger, two of the Academy's correspondents, gave in several Memoirs in which that business is described with great accuracy, from their own view on the spot. Their Memoirs inform us, that chimney-soot alone, without any additament, is the matter from which they obtain their Sal Ammoniac; that those chimneys under which nothing is burnt but Cow's-dung furnish the best Soot. Six and twenty pounds of that Soot yield usually six pounds of Sal Ammoniac.

"The operation takes up about fifty, or two and fifty hours. The vessels in which they put the soot are ballons of very thin glass, terminating in a neck of fifteen or sixteen lines long, and an inch in diameter: but they are not all of the same size. The least contain twelve pounds of Soot, and the greatest fifty; but they fill them only three quarters full, in order to leave room for the sublimation of the Salt.

"The furnace, in which they place these ballons, consists of four walls, built in a quadrangular form. The two front walls are ten, and the sides nine feet long: but they are all five feet high, and ten inches thick. Within the quadrangle formed by these walls three arches run lengthwise from end to end thereof, at the distance of ten inches asunder. The mouth of this furnace is in the middle of one of its fronts, and of an oval form; two feet four inches high, and sixteen inches wide.

"The ballons lie in the spaces between the arches of the furnace, which serve instead of a grate to support them. Four of them are usually placed in each interval; which makes sixteen for one furnace. They are set at the distance of about half a foot from each other, and secured in their places with brick and earth. But they leave about four inches on the upper part of the ballon uncovered, with a view to promote the sublimation, as they also do six inches of the inferior part, that the heat may the better act on the matters to be sublimed. Things being thus prepared they first make a fire with straw, which they continue for an hour. Afterwards they throw in Cow's-dung made up in square cakes like bricks. (The want of wood in this country is the reason that they generally make use of this fuel). These cakes of dung add to the violence of the fire, which they continue in this manner for nineteen hours; after which they increase it considerably for fifteen hours more; and then they slacken it by little and little.

"When the matter contained in the vessels begins to grow hot, that is, after six or seven hours baking, it emits a very thick and ill-scented smoke, which continues for fifteen hours. Four hours after that, the Sal Ammoniac is observed to rise in white flowers, which adhere to the inside of the neck of the vessel; and those who have the direction of the operation take care, from time to time, to pass an iron rod into the neck of the ballon, in order to preserve a passage through the saline vault, for giving vent to some blueish vapours, which constantly issue out of the vessel during the whole operation."