514 PLINY'S NATUBAL HISTORY. [Book XXXI. 



stones. It is prepared in pretty nearly the same manner 73 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, 73 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 74 

 and in certain springs in the vicinity of Chalcis, the water is 

 fresh and potable on the surface, and 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 75 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. 76 



The only nitre-works in Egypt were formerly those in the 

 vicinity of Naucratis 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 77 on 



72 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. 



73 Of a bituminous nature, probably. See c. 42 of this Book. 



74 See B. v. c. 40. An alkaline water, Beckmaun thinks. See Vol. II. 

 pp. 96-7. Bohn's Ed. 



75 He may possibly mean bleaching the material before dyeing. 



76 See B. xxxvi. c. 65. This certainly goes far towards proving that 

 under the name " nitrum," alkaline salts were included. 



41 " Faciunt ex his vasa ; necnon frequenter liquatum cum sulphure, co- 



