slacked lime with ground peat, and then to distill for ammonia.

In the year 1794, Lelievre, Pelletier, D'Arcet, and Giroud, eminent French chemists, were employed by the Committee of Public Safety in Paris, to make a Report on the divers means of extracting soda from sea salt with advantage; and they, in their account of that process, have given one which was at that time conducted by M. Leblanc, at St. Denis near Paris, for the manufacture of sal-ammoniac 20.

His method consists in decomposing muriate of soda by sulphuric acid in a kind of reverberatory furnace, the floor of which is covered with lead; and as the current of muriatic gas is determined into an adjoining leaden chamber, it is there, at the same instant, met by a current of volatile alkali, produced from a variety of animal matters, which they burn in three cylinders of iron, placed in a furnace, side by side of each other.

In this process, the vapours of the muriatic salt; are condensed in the leaden chamber, not only by their combination with the ammonia", but also by means of an eolipile, which was heated by the same

20 An extract from this Report was printed in the Annales de Chimie, tom. xix. page 58.

If the stopper be taken out of a phial of muriatic acid, in the presence of some liquid ammonia, it will be seen, by the cloud of muriate of ammonia in vapour which will appear in the atmosphere, how eager these gases are to unite to form the new compound.

furnace in which the iron cylinders were fixed for the combustion of the animal substances.

The decomposition of the muriate of soda was not, however, entirely finished in this operation, because the sheet of lead which covered the floor of the reverberatory furnace could not, without melting, endure a degree of heat sufficiently strong to effect this purpose. The operator therefore moves the matter into a third reverberatory furnace paved with brick, where it receives a degree of heat sufficient to make it enter into fusion, and complete the decomposition. It was necessary for the proprietors of this establishment to complete the decomposition of the common salt, because the economy of their process consisted in the employment of the alkaline residuum for the production of cry. stallized soda.

This ingenious method of making sal-ammoniac is described likewise in the second volume of the Journal de Physique for the year 1794, p. 134, and it is there accompanied with a copper-plate engraving of the ground-plan of the furnaces and other apparatus employed in the process. This apparatus is so very different from any thing which I have seen in this country, and at the same time is so well contrived for the purpose, that I have thought it worth while to copy it and have it engraved, to accompany this Essay".

There is, however, a mode of making sal-ammo

See Plate 23 at page 437 of this volume.

niac, which I conceive would be more economical than any of those already mentioned. It consists in the employment of the bittern of the salt-works, or the mother-waters which remain after the extraction of common salt from sea water. This is not a mere theoretical notion, for the process has more than once been acted upon, and at this time large quantities of sal-ammoniac are actually made according to this principle in some parts of Scotland.

The desire of making this valuable and economical process for preparing muriate of ammonia from the bittern of the salt-pans more generally known, was the motive that induced me to render the manufacture of sal-ammoniac one of the subjects of these Essays.

The preparation of this important salt by means of bittern is not, as I have said, a new process, for I recollect reading an account of it many years ago in one of the volumes of the Annales de Chimie 23, and in other works; but knowing the Board of Excise in England would neither allow the use of bittern, nor even the burnt pickings of the salt-pans, free of excise duty, I imagined this to be one of those processes which are interdicted by the high price of the materials, till an accidental circumstance which occurred a few years ago recalled my attention to the subject in a very particular manner.

43 See Annales de Chimie, tom. xx. page 186.

Mr. Astley of the town of Borrowstoness near Leith, who had taken out a patent for the manufac ture of sal-ammoniac by combustion, in which he proposed to burn bones, blood, and other animal matters, with the bittern, proceeded by due course of law against a gentleman of the same town for having infringed his patent, and the cause came to be tried before the Lords of Session in Scotland. The question, however, not having been determined by the Court, it was agreed between the parties to defer final judgement until the opinions of some practical chemists in London should be obtained on the subject; and it was during my examination before the Commissioner appointed by the Lords of Session to take our report, that I first obtained the information that the Board of Excise allows the inhabitants of Scotland the bittern of the salt-works free of duty.

On acquiring a knowledge of this fact, a question immediately occurred-If the inhabitants of one part of the empire are allowed an article which is capable of being used in our manufactories duty free, why should not the same indulgence be universal in England and Ireland, as well as in Scotland?

Reflecting still more and more on this subject, and knowing that the riches of a country depend in a great measure on its producing within itself

24 Dr. Thomson says, that if the fibrous part of blood be left in water it soon putrifies, and then yields more ammonia than any other animal substance.

most of the articles required for its own consumption, I think it right to make this circumstance more generally known; in the hope that some competent person, possessing the advantages of capital and a favourable locality of situation, would petition the legislature for leave to commence such an undertaking, and thus relieve the country from the necessity of sending into another quarter of the globe for a supply of this valuable and necessary commodity.

If a company of persons accustomed to the manu

facture of sal-ammoniac was established in the neighbourhood of any of the salt-works in Cheshire, or near the salt-pits of Droitwich in Worcestershire, and could obtain permission from Government to use the bittern which is produced at either of those establishments, and which at present is thrown away as a useless residuum, I am certain that such a company would be enabled to afford the article in question much cheaper than the English sal-ammoniac has been sold for many years past, and at a rate which would effectually prevent the importation of ammoniacal salt from any part of the East. There are considerable salt-works in the Isle of Wight, and on the opposite coast at Lymington in Hampshire; but at both these establishments the salt is procured by the evaporation of sea water.

About a century ago, a work of the kind which I have here recommended, was established by one Goodwin a chemist of London 25, in which he pro

25 Institutes of Experimental Chemistry, 2 volumes octavo, printed by Nourse, London 1759, vol. i. page 347.