514 
plint's natural history. 
[Book XXXI. 
stones. It is prepared in pretty nearly the same manner^^ as 
salt, except that in the salt-pans it is sea- water that is intro- 
duced, whereas in the nitre-beds it is the water of the river 
Mlus ; a water which, upon the subsidence of the river, is 
impregnated with nitrum for forty days together, and not, as in 
Macedonia, at intermittent periods only. On occasions when 
there has been a fall of rain, a smaller proportion of river- 
water is employed. As soon, too, as any quantity of nitrum 
has formed, it is immediately removed, in order that it may not 
melt in the beds. This substance, also, contains a certain 
proportion of oil,"^^ which is very useful for the cure of scab in 
animals. Piled up in large heaps, it keeps for a very con- 
siderable time. It is a marvellous fact, that, in Lake Ascanius^'* 
and in certain springs in the vicinity of Chalcis, the water is 
fresh and potable on the surface, arid nitrous below. The 
lightest part of nitrum is always considered the best, and hence 
it is that the froth of it is so much preferred. Still, however, 
when in an impure state, it is very useful for some purposes, 
colouring purple^^ cloth, for instance, and, indeed, all kinds of 
dyeing. It is employed, also, very extensively in the manu- 
facture of glass, as we shall more fully mention on the appro- 
priate occasion."^ 
The only nitre-works in Egypt were formerly those in the 
vicinity of JN'aucratis and Memphis ; those near Memphis being 
inferior to the others, the piles of nitrum there prepared 
being as hard as stone, and many of the heaps having 
become changed into rocks. When in this state, vessels are 
made of it, and very frequently they melt it with sulphur'^ on 
'^'^ Ajasson remarks, that from this we may conclude that the fabrication 
of nitrate of potash, or saltpetre, was in its infancy. It is by no means 
improbable that the artificial nitrum, here mentioned by Pliny, really was 
artificial saltpetre, more or less impure ; the native nitrum, on the other 
hand, being, as Beckmann suggests, a general term for impure alkaline 
mineral salts, in common with native saltpetre. Pliny's account, however, 
is confused in the highest degree, and in some passages far from intel- 
ligible. 
Of a bituminous nature, probably. See c. 42 of tbis Book. 
"^^ See B. V. c. 40. An alkaline water, Beckmann thinks. See Vol. IL 
pp. 96-7. Bohn's Ed. 
He may possibly mean bleaching the material before dyeing. 
^6 See B. xxxvi. c. 65. This certainly goes far towards proving that 
under the name "nitrum," alkaline salts were included. 
" Faciunt ex his vasa, necnon frequenter liquatum cum sulphure, co- 
