VOL. LXI.j PHILOSOPHICAL TRANSACTIONS. 217 



salt which now goes by the name of nitre, or saltpetre; but a salt of an alkaline 

 nature, which at present is commonly called the natron of the ancients, or the 

 fossil alkali. The knowledge of it was entirely lost for several centuries; but 

 was revived in the last, by the Hon. K. Boyle, who, in his Short Memoirs for 

 the Natural Experimental History of Mineral Waters, ^ after telling us that it is 

 of an alkaline nature, says, ' that he had some of it brought from Egypt, and a 

 neighbouring country, whose name he did not remember.' 



However, it was afterwards neglected, and its properties as a distinct species 

 of alkaline salt not known for many years; for though chemists observed, 

 that a Glauber salt and cubic nitre were formed by dislodging the marine acid 

 from sea-salt, by means of the vitriolic and nitrous acids ; and from thence sus- 

 pected that there was something particular in the basis of this salt ; yet its true 

 nature was not discovered till Mons. du Hamel du Monceau gave an account, in 

 the Memoirs of the French Royal Academy of Sciences for the year 1736, of 

 his having obtained it pure, in two different ways. 1 st. By dislodging the marine 

 acid by means of the vitriolic, and then separating it by the addition of a phlo- 

 giston, and forming a hepar sulphuris, from which he precipitated the sulphur 

 by means of the vegetable acid, and then separated this acid from the basis of 

 sea-salt by the force of fire. 2d. By dislodging the marine acid from the sea- 

 salt by the addition of the nitrous, and so forming a cubic nitre, from which he 

 dislodged the acid, by deflagrating it with charcoal ; and then he purified the 

 remainder by dissolving it in water, and by filtrating and evaporating the liquor 

 and crystallizing the salt. 



After he had obtained the basis of sea-salt quite pure, he tried a number of 

 experiments with it, and with the natron of Egypt; and found that they were 

 entirely of the same nature, and that they were of a distinct species of alkaline 

 salt, different in their properties from the potash, and other alkaline salts, com- 

 monly obtained by burning wood, and most other vegetable substances ; and that 

 they formed different neutral salts with the 3 mineral acids, and with the vege- 

 table. This salt is likewise got from burning the barilla, the kali, and other 

 marine plants; and all that is at present used in this country, by our manufac- 

 turers, has been prepared in this manner. 



Hitherto it has not been found native in the western parts of Europe, except 

 in mineral waters, and in the neighbourhood of volcanos, or at places where 



Tacitus, in mentioning the river Belus in India, says, ' Circa cujus os collectae arenae, admixto 

 nitro, in vitrum excoquuntur.' Lib. v. Hist. sect. 7. — Orig. 



f Nitre is mentioned as used in baths, in several parts of the Holy Scripture, particularly by the 

 prophet Jeremiah. See chap. ii. ver. 22. The nitre, or natron, is likewise taken notice of by many 

 other of the ancient authors. — Orig. 



J See his notes on title 26, p. 86, of the edition printed at London IG84-5. — Orig. 



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