BOOK XII. 



559 



A — Nile. B — Nitrum-pits, such as I conjecture them to be.' 



verted into nitrum. Just as the sea, in flowing of its own will over the soil 

 of this same Egypt, is changed into salt, so also the Nile, when it overflows 

 in the dog days, is converted into nitrum when it flows into the nitrum pits. 

 The solution from which nitrum is produced is obtained from fresh water 

 percolating through nitrous earth, in the same manner as lye is made from 

 fresh water percolating through ashes of oak or hard oak. Both solutions 

 are taken out of vats and poured into rectangular copper caldrons, and are 

 boiled until at last they condense into nitrum. 



in the volcanoes in Italy, it also may have been included in the nitrum mentioned. Nitrum 

 was in the main exported from Egypt, but Theophrastus mentions its production from 

 wood-ash, and Pliny very rightly states that burned lees of wine (argol) had the nature 

 of nitrum. Many of the ancient writers understood that it was rendered more caustic by 

 burning, and still more so by treatment with Ume. According to Beckmann (Hist, of Inven- 

 tions II., p. 488), the form of the word natron was first introduced into Europe by two 

 travellers in Egypt, Peter Ballon and Prosper Alpinus, about 1550. The word was intro- 

 duced into mineralogy by Linnaeus in 1736. In the first instance natron was applied to 



'This wondrous illustration of soda-making from Nile water is no doubt founded upon 

 Pliny (xxxi., 46). " It is made in almost the same manner as salt, except that sea-water 

 " is put into salt pans, whereas in the nitrous pans it is water of the Nile ; these, with the 

 " subsidence of the Nile during the forty days, are impregnated with nitrum." 



