Page:History of the Royal Society.djvu/288

 indeed this greasy Oyl (which the Workmen call Mother of Salt-peter, and perhaps is but the crude and unripe part of it) doth by nature so wonderfully adhere to every part else of the Peter (it may be ordained for the nutriment and augmentation of it) that the reparation of it, is the sole cause of the great charge and labour that is required to the refining of Peter: otherwise the Peter will be yellow, or brown, or some other dark colour. And Scaliger in his 104. ''Exercit. sect''. 15. saith, Sublustris purpuræ quasi splendor quidem in salis-petræ terris saepenumero est a nobis observatus; and he that shall boil a Lixivium past through a Salt-peter-earth, up to a consistence, without filtring it through ashes, or giving the Salt leave to chrystallize, may perhaps find something not unlike the Nitre of the Antients.

'To make this doubt yet clearer, it will require your patience to observe a few short remains out of the same Pliny, concerning the production of Nitre; saith he, Exigiuum Nitri fit apud Medos, candescentibus siccitate convallibus quod vocant Halmirhaga: minus etiam in Thracia juxta Philippos sordidum Terra quod appellant Agrium.

'This agrees very exactly with what I have been informed by a Refiner of Salt-peter, that near Sophia, Santa Crux, and several other places in Barbary, he hath seen Salt-peter shoot out of the ground (as thick and white as a hoar frost) on many barren and desart Lands; only he adds, that this happens not till the beginning of the rains of August, or September; and that it is the falling of the fresh-water that causes the Salt peter to shoot out into little Chrystals; and that the people of the Rh