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Upon burning fea-wrack to a black coal, and flopping the I process at that point, I have obtained great plenty of common. falt, but no mineral alcali from the black afhes; though we are certain, that when the black afhes are thoroughly calcined, or reduced to white afhes, mineral alcali may be obtained from them. This makes it probable, that the common falt, contained in the black afhes of fea-wrack, is decompofed, and changed into a mineral alcali, during the burning of the black afhes.'
We apprehend, however, that, if the Author had minutely attended to the different products refulting after the calcination of the black afhes above mentioned, he would have found that fea falt cannot fo eafily be decompounded by this calcination, as he feems to expect. In fact, a confiderable fhare of attention has lately been bestowed on this very fubject, by Mefirs. Macquer and Poullettier de la Salle; who found the produce of mine-ral alcali, even from the white afhes, to be very fmall. It appears, for inftance, that the faline matter obtained from feawrack, or Varec, as it is called by the French, calcined during the space of three hours, was a heterogeneous mafs, confifting principally of Glauber's falt, together with vitriolated tartar, fea falt, fal Sylvii, hepar fulphuris, Stahl's fulphureous falt, felenite, and but a fmall quantity of mineral alcali; the production of a 'great part of which laft may be naturally accounted for, from the decompofition of the Glauber's falt, and the production of a hepar fulphuris with an excefs of alcali; which may be fuppofed to take place, by means of the phlogiston, or inflammable principle, of the plant, combining with the vitriolic acid in the Glauber's falt. Nor, confidering the fmall quantity of mineral alcali obtained in their trials, is there any reafon to fuppofe that any confiderable portion of it had been procured in confequence of any direct decompofition of the fea falt contained in the Verec, by the action of the coal upon it.
It is rather furprifing that, in the prefent extenfive profecution of chemical enquiries, no eafy or cheap method has yet been discovered, or at least published, of procuring the foffil alcali, fo abundantly contained in fea falt; by expelling the marine acid from it, without introducing another acid in its place. On this fubject, however, we fhall juft ftop to observe, that we are acquainted with a very fimple procefs, not the refult of defign, but of accidental obfervation, in which this feparation is effected; and in which fea falt, merely by lying in contact with a metallic body, expofed to the air, is in a fhort time wholly decompounded: the acid totally disappearing, and the alcaline bafis of the fea falt being left in a pure ftate, and impregnated with fixed air. But we know not yet, whether this procefs, though it fucceeds in small trials, can be profecuted to advantage on a large fcale.
In the fourth Effay are contained fome general obfervations on fire, fulphur, and phlogiston; which are followed, in the next Eflay, by others refpecting the origin of fubterraneous fires; and which are principally founded on the phenomena attending the decompofition of pyrites, and on Lemeri's well known experiment made with fulphur and iron filings formed into a paste with
In the fixth Effay, an account is given of the vitriols, and of the apparent tranfmutation, as it was at firft fuppofed to be, of iron into copper, on the immerfion of iron bars in water. naturally impregnated with copper diffolved in the vitriolic acid. In the feventh, the Author treats of nitre, and relates the wellknown experiments made with its acid, in kindling oils, and freezing quickfilver when added to fnow, &c.
In the eighth Effay, the Author treats of the manner of making faltpetre in Europe, and of its generation. This is indeed a curious fubject, whether it be confidered in a philofophical, or in an economieal and political light. In the latter view, we find that it has lately fo far excited the attention of the French ministry, on account of the fucceffive diminution of the produce of the nitre-works which have been long established in that kingdom; that, in confequence of an application from M. Turgot to the Royal Academy of Sciences at Paris, a prize of 4000 livres, and two others of 1200 and 800, have been offered by the king for the best differtation on the fubject. And to give all those who should contend for this prize all the information poffible relative to it, a large octavo volume has been published containing all the valuable effays or fcattered obfervations refpecting this fubject, that have appeared fince the time of Glauber.
I do not know,' fays the Author, that we have at present ⚫ any faltpetre works established in England. There have been ' many projects proposed for making it, both in the last and prefent century; but they have all ended more to the difadvantage than the emolument of the undertakers. The fociety for 'the encouragement of arts and manufactures in vain proposed premiums for the making of faltpetre, from the year 1756 to 1764: thefe premiums were never claimed, and a faltpetre work, which was about that time established at the expence of above L. 6000, was at laft abandoned; the proprietors having ⚫ been experimentally convinced, that they could not afford to
fell their faltpetre for less than four times the price of that ⚫ imported from India.'The caufes of this conftant failure in all attempts to make faltpetre with profit in England are, according to the Author, the high price of labour, and partly the unfavourableness of the climate; but principally the dearnefs of the wood afhes generally used in this manufacture.
The Author, however, queftions how far a fixed alcali of wood afhes are, in all cafes, neceffary for the extraction of this falt from the earths which contain it. On this head he relates the following obfervation:
From an old barn, belonging to the Dean and Chapter at Ely, I took fome decayed mortar, which was full of thofe faline fhoots frequently feen on old walls, and boiled it in a proper quantity of water. The water being filtered and evaporated, afforded, in great plenty, well formed crystals of faltpetre. The cryftals were taken out and dried, and the remaining part of the folution was again evaporated, and it again yielded very good faltpetre; but I could not obferve that there was any occafion for wood afhes, to make any part of the folution crystalize; or that there were formed any cryftals either of fea-falt or of any other falt, except faltpetre.'
The Reviewer of the prefent article can confirm this obfervation of the Author's from his own experience; having fome years ago collected a pretty large quantity of faline efflorescences from the walls of the ancient abbey at Caftleacre in Norfolk; some of which was indeed calcareous nitre; but a confiderable portion taken from another part of the building, was found to be true nitre, with an alcaline bafis-(whether vegetable or foffil, he neglected to obferve), as he afcertained by various trials; particularly by deflagrating it with charcoal, &c. Since the late difcovery of the method of obtaining a fixed alcali from putrid vegetable and animal fubftances *, it might be fuppofed, that the pure nitre, in the two cafes above-mentioned, might derive its alcaline bafis from moffes and other vegetables fucceffively growing and rotting on the walls, or from the dung of birds. left there but perhaps the following obfervation may point out its real origin.
M. Pietfch, who feveral years ago obtained the prize given by the Royal Academy of Berlin, for the beft differtation on the production of faltpetre, and which is printed in the collection above-mentioned, obferves, that on tafting fome faline efflorescences, which appeared on a wall conftructed only of ftones and mortar, and which tafted like pure faltpetre, he examined them more particularly, and obtained from the folution genuine cryftals of cubic nitre. The wall appears to have been one of those built in confequence of an ordinance of the King of Pruffia, for the fole purpose of generating what is called crude faltpetre: and M. Pietsch supposes that through accident fome fea-falt had been mixed with the mortar employed in the construction of it. He takes for granted that fea-falt, on being merely ex
* See our account of Dr. Percival's Paper on this fubject, in our Review for April lat, p. 272. • pofed
pofed to the air, changes its nature, and is converted into an an alcaline falt.' We know not on what grounds M. Pietfch founds this affertion: we fhould rather be inclined to fuppofe that, in the prefent cafe, calcareous nitre had first been formed; and that, in time, the two acids had refpectively changed bafes. The Author feems to confider the queftion How is faltpetre generated?'-as infoluble; or at leaft modeftly confeffes his own inability to answer it, in a manner fatisfactory to himfelf. We too confefs ourfelves, perhaps equally, unable at prefent to folve this problem; though we are far from 'concurring with the Author in opinion, that all that philofophy can fay on the fubject seems to be included in the anfwer of the Spaniard; who was asked if he knew how the faltpetre was yearly regenerated in his grounds?" I have two fields," fays he : "in the one I fow wheat, and it grows; in the other I collect "faltpetre *."
The accounts which we have yet received from Spain, as well as other countries, refpecting the large crops of faltpetre produced from the fame land annually, and without any addition of fixed alcali in the fubfequent manufacture, have not been fufficiently numerous, nor have the particulars of the whole procefs, perhaps, been obferved with the requifite attention, even by M. Bowles. It is true, as the Author obferves, that the parts of matter are fubjected to perpetual change, and forced to affume new arrangements: and that the fweet, bitter, and aromatic juices of vegetables; the blood, bile, milk, urine, fat, and bones of animals, are all of them as different from the fubftances from which they are compofed, as faltpetre is from the ' earth from which it is generated. A confideration of thefe great changes, however, operated in the organized bodies of animals and vegetables, poffeffed of the principle of life, will not, ftriking as they are, eafily familiarize a chemift to the idea that inert, unorganized earth, which has had all its parts that are foluble in water previously extracted from it, can by mere exposure to the air be tranfmitted into true faltpetre. The changes here compared together by the Author are not ftrictly fimilar. The fuppofed annual tranfmutation of vegetable earth into fixed alcali, &c. is a procefs ftrictly chemical; whereas the various and wonderful changes which the food of living animals and vegetables undergoes, and which are principally effected by their various fecretory organs, and by powers exercifed only during life, are, in certain refpects, at leaft, the effects of caufes which by no means fall under the cognizance of chemistry.
See Bowles's hiftoire naturelle de l'Espagne, p. 80; or our account of it in the Appendix to our 59th volume, July 1778. P. 539.
Before we quit this fubject, we shall tranfcribe the following obfervation of the Author's; which, confidering the tenure by which we hold our Eaft India poffeffions, certainly deferves the attention of government.
About the fame period (1693) that the government of England bargained with the Eaft-India Company for an annual fupply of faltpetre, a much larger quantity was made in France; an author of good credit informing us that, in the year 1691, the faltpetre, which was made in the feveral districts of that < kingdom, amounted to 3,647,767 pounds. This is a vast quantity, being nearly equal to the average quantity annually imported by our Eaft-India Company. The French very wifely keep up their eftablishments for the making of faltpetre: the revo•lutions which have formerly taken place in India, render it not improbable that fimilar ones may take place again; and England would feel the diftrefs which would attend the non-importation of faltpetre from the Eaft-Indies, more fenfibly than any other ftate in Europe. This danger has not been adverted to by any minifter; but if the prevention of it should ever engage the attention of the legiflature; the methods of making faltpetre which are followed in France, would deferve to be confidered. For my own part, I can have no doubt that a plan might be contrived for the making of faltpetre in every county of this kingdom, by the very moderate labour of those whofe idleness is at prefent a burden to themfelves, and a reproach to the police of the community, the paupers of the feveral parishes.'
With a view to this fubject, the Author recommends to the Reader's perufal a very good paper of Mr. Henfhaw's, in Bishop Sprat's Hiftory of the Royal Society-Newman's Chemistry tranflated and published by Dr. Lewis-Glauber's Prosperity of Germany-Clarke's Natural History of Saltpetre- and the account of the manner of preparing this falt, defcribed in the Philofophical Transactions 1763. To fecond the Author's patriotic views, we shall add the title of the ftill more comprehenfive and fatisfactory collection of tracts relative to this fubject, which, as we have already obferved, has been compiled by the commiffaries of the Academy of Sciences at Paris; where it was published in the year 1776, under the title of Recueil de Memoires Fabrication du fal
et d'Obfervations fur la Formation et fur la petre, 8vo, Lacombe.'
In the ninth Effay, the contents of which we have in some measure anticipated, the Author treats of the manner of making faltpetre in the Eaft-Indies; and in the tenth, which terminates the first volume, he difcuffes the queftions, at what time gunpowder was difcovered, and when it was firft applied to the ⚫ purposes of war,'