That neutral salt mentioned above, which is formed by combining the Marine Acid with a common fixed Alkali, and called _Sal febrifugum Sylvii_, hath also this property. India furnishes us with a saline substance, known by the name of _Borax_, which flows very easily, and then takes the form of glass. It is of great use in facilitating the fusion of metallic substances. It possesses some of the properties of fixed Alkalis, which has induced certain Chymists to represent it, through mistake, as a pure fixed Alkali. By mixing borax with the vitriolic Acid, Mr. Homberg obtained from it a salt, which sublimes in a certain degree of heat, whenever such a mixture is made. This salt has very singular properties; but its nature is not yet thoroughly understood. It dissolves in water with great difficulty; it is not volatile, though it rises by sublimation from the borax. According to Mr. Rouelle's observation, it rises then only by means of the water which carries it up: for, when once made, it abides the fiercest fire, flows and vitrifies just as borax does: provided care be taken to free it previously from moisture by drying it properly. Mr. Homberg called it _Sedative Salt_, on account of its medical effects. The sedative salt hath the appearance, and some of the properties, of a neutral salt; for it shoots into crystals, and does not change the colour of violets; but it acts the part of an Acid with regard to Alkalis, uniting with them to the point of saturation, and thereby forming a true neutral salt. It also acts, like the Acid of vitriol on all neutral salts; that is, it discharges the Acid of such as have not the vitriolic Acid in their composition. Since Mr. Homberg's time it hath been discovered, that a sedative salt may be made either with the nitrous or with the marine Acid; and that sublimation is not necessary to extract it from the borax, but that it may be obtained by crystallization only. For this latter discovery we are indebted to Mr. Geoffry, as we are to Mr. Lemery for the former. Since that time M. Baron d'Henouville, an able Chymist, hath shewn that a sedative salt may be obtained by the means of vegetable Acids; and hath lately demonstrated, in some excellent papers published in the collection of Memoirs written by the correspondents of the Academy of Sciences, that the sedative salt exists actually and perfectly in the borax, and that it is not produced by mixing Acids with that saline substance, as it seems all the Chymists before him imagined. This he proves convincingly from his analysis of borax, (which thereby appears to be nothing else but the sedative salt united with that fixed Alkali which is the basis of Sea-salt) and from his regenerating the same borax by uniting together that Alkali and the sedative salt: a proof the most complete that can possibly be produced in natural philosophy, and equivalent to demonstration itself.