sprinkled on it, a little at a time. The sulphur deflagrating was supposed to exercise the purifying influence on the nitre. The actual effect was to convert a small part of the nitrate of potash into sulphate. It was first called Sal Prunella in Germany from the belief that it was a specific against a certain plum-coloured quinsy of an epidemic character. Boerhaave advised the omission of the sulphur, but believed that melting the pure nitre and moulding it was of medicinal value by evaporating aqueous moisture.
Nitre and flowers of sulphur were deflagrated together before the Sal Prunella theory was invented, equal quantities being employed. The resulting combination, which was of course sulphate of potash, was known as Sal Polychrestum, the Salt of Many Virtues.
Sal Gemmæ.
Sal Gemmæ or Sal Fossile was the name given to rock salt, particularly to the transparent and the tinted varieties. It was believed to be more penetrating than the salt derived from sea water, and this property Lemery ascribed to the circumstance that it had never been dissolved in water, and therefore retained all its native keenness.
Spirit of Salt.
Spiritus Salis Marini Glauberi was one of the products discovered by Glauber, to whom we owe the name of spirit of salt. He was a keen observer and remarked on the suffocating vapour yielded as soon as oil of vitriol was poured on sea salt. It is astonishing to his biographers that he just missed discovering chlorine. The spirit of salt was highly recommended for many medicinal uses;
