516 PLINY'S NATURAL HISTORY. [Book XXXI. 



vessels pitched within, to prevent its melting, 83 the vessels 

 being previously prepared by being thoroughly dried in the 

 sun. 84 



To be good, nitrum should be very fine, and extremely 

 spongy and porous. In Egypt, it is sophisticated with lime, 

 an adulteration easily detected 85 by tasting it ; for when pure, 

 it liquefies immediately, while that which has been adulte- 

 rated, remains undissolved sufficiently long to leave a pungent 

 taste 86 in the mouth. It is burnt in a close earthen vessel, as 

 otherwise it would decrepitate : 87 except in this last case, how- 

 ever, the action of fire does not cause it to decrepitate. This 

 substance neither produces nor nourishes anything ; while, in 

 the salt-pans, on the other hand, we see plants growing, and 

 the sea, we know, produces immense numbers of animated 

 beings, though, as to plants, sea-weed only. It is evident, too, 

 that the acridity 88 of nitrum must be much greater than that 

 of salt, not only from the fact last mentioned, but from the 

 circumstance also, that at the nitre-beds the shoes wear out 

 with the greatest rapidity ; localities which are otherwise very 

 healthy, and remarkably beneficial for the eye-sight. At the 

 nitre- works ophthalmia is a thing unknown : persons, too, 

 that come there with ulcers upon them experience a rapid 

 cure ; though ulcerations formed upon the spot are but slow 

 in healing. Used as a friction with oil, nitrum is a sudorific, 

 and acts emolliently upon the body. That of Chalastra is 

 used as a substitute for salt, in making bread, 89 and the Egyp- 



83 One proof, Beckmann thinks, that Soda is meant. See Vol. II. p. 

 491. 



84 " Whether Pliny means that the vessels were not burnt, hut only 

 baked in the sun, or that before they were filled, they were completely 

 dried in the sun, has been determined by no commentator. To me the 

 latter is probable." Beckmann, Hist. Inv. Vol. II. p. 491. 



85 Beckmann thinks that this mode of adulteration, with lime, is an 

 additional proof that the " nitrum " of our author was only soda. See 

 Vol. II. p. 492. 



86 That, namely, of the lime. Quick-lime, certainly, would have a pun- 

 gent taste, in comparison with that of soda, but not in comparison with 

 that of saltpetre. 



87 Another proof, Beekmann thinks, that it was native soda, impregnated 

 with common salt. Vol. II. p. 492. 



18 This would hardly apply to soda. 



89 Probably to promote its rising, as Beckmann observes, Vol. II. p. 

 496 ; a circumstance which goes a great way towards proving that " Soda" 



