516 
PLINT'S NATUEAL HISTOEr. 
[Book XXXI. 
vessels pitched within, to prevent its melting,®^ the vessels 
being previously prepared by being thoroughly dried in the 
sun.®^ 
To be good, nitrum should be very fine, and extremely 
spongy and porous. In Egypt, it is sophisticated with lime, 
an adulteration easily detected^^ 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^^ in the mouth. It is burnt in a close earthen vessel, as 
otherwise it would decrepitate i^"^ 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^^ 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, and the Egyp- 
One proof, Beckmann thinks, that Soda is meant. See Vol. II. p. 
491. 
84 « Whether Pliny means that the vessels were not burnt, but 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. 
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. 
^6 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. 
Another proof, Beckmann thinks, that it was native soda, impregnated 
with common salt. Vol. II. p. 492. 
88 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" 
