Chap. 46.] VARIOUS KINDS OF NITEUM. 515 



a charcoal fire.' 8 When substances 79 are wanted to keep, they 

 employ this last kind of nitrum. In Egypt there are also nitre- 

 beds, the produce of which is red, owing to the colour of the 

 earth in the same locality. Froth of nitrum, 80 a substance 

 held in very high esteem, could only be made, according to the 

 ancients, when dews had fallen ; the pits being at the moment 

 saturated with nitrum, but not having arrived at the point of 

 yielding it. On the other hand, again, when the pits were in 

 full activity, no froth would form, it was said, even though 

 dews should fall. Others, again, have attributed the formation 

 of this last substance to the fermentation of the heaps of 

 nitrum. In a succeeding age, the medical men, speaking of it 

 under the name of " aphronitrum," 81 have stated that it was 

 collected in Asia, where it was to be found oozing from the 

 soft sides of certain mines the name given to which was 

 " colyces" 82 and that it was then dried in the sun. The very 

 best is thought to be that which comes from Lydia ; the test of 

 its genuineness being its extreme lightness, its friability, and 

 its colour, which should be almost a full purple. This last is 

 imported in tablets, while that of Egypt comes enclosed in 



quentes in carbonibus." This passage Beckmann pronounces to be one of 

 the darkest parts in the history of nitrum. See Vol. II. p. 502. lie is of 

 opinion that not improbably the result here obtained would be, liver of 

 sulphur, which when it cools is hard, but soon becomes moist when ex- 

 posed to the air. Dalechamps, it would appear, explains the whole of this 

 passage as applicable to glazing ; but in such case, as Beckmann observes, 

 the nitrum could serve only as a flux. Michaelis suggests that the vessels 

 here mentioned, were cut, not for real use, but merely for ornament, in the 

 same manner as they are still made, occasionally, from rock-salt. 



755 The mention of nitrum, sulphur, and charcoal, probably the three 

 ingredients of gunpowder, in such close proximity, is somewhat curious. 



79 " Quae " seems a preferable reading to " quos." 



80 " Spuma nitri." An accidental property, Beckmann says, of the 

 same salt that has been previously called " Chalastricum," " Halmyrax," 

 " Aphronitrum," and " Agrion." In his opinion, " the ancients were ac- 

 quainted with no other than native nitrum, which they called artificial, 

 only when it required a little more trouble and art to obtain it." Hist. 

 Inv. Vol. II. p. 502. Bohrfs Ed. 



81 " Froth of nitre." Ajasson identifies this with hydro-carbonate of 

 soda. 



82 Supposed by Hardouin to be derived from the Greek jeoAiKac, "round 

 cakes;" owing to the peculiar form of the pieces of rock by which the 

 aphronitrum was produced. The reading, however, is very doubtful. 

 Sillig, from Photius, suggests that it should be " scolecas." 



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