VOL. XIV.] PHILOSOPHICAL TKANSACTIONS. 5l 



The natron may be described thus: it is an alkaline salt perforated like a 

 sponge, and of a lixivial taste, and thus I find it described by Pliny, Mathiolus, 

 and Agricola. 



Its principles I take to be chiefly two, viz, a sal marine,* and a urinous salt, 

 (vol. alkali.) 



The Nitrian water is of a blushy colour, and makes a brisk fermentation with 

 an acid. I suppose that the water of Natron receives its redness from a red 

 clammy substance.-J- 



The next thing to be considered, is its separation from the water of Natron, of 

 which the learned Dr. Huntington, who was at Nitria, gives the following ac- 

 count : 



There is a town in Egypt called Nitria, which gives name to the Nitrian de- 

 sert, where there is a lake called Natron,;}: taking up an area of 6 or 7 acres, 

 situate about 30 miles west and by south from Terana, a town lower upon the 

 Nile than Grand Cairo, and about the same distance north-west from the pyra- 

 mids ; from the bottom of this lake this sort of nitre called Natron arises to the 

 top (as they apprehend) and there by the heat of the sun condenses into this 

 kind of substance.^ 



The next thing to be considered is its use in physic: by Pliny it is com- 

 mended in ulcers, inflammations, palsy in the tongue, consumptions, colic, 

 hemorrhages, &c. &c. 



Some authors assert it to be of wonderful efficacy in the stone.|j 



The next thing to be considered is its use in agriculture. 



Mr. de la Cambre says, that plants grow in Egypt in such abundance, that 

 they would choke each other, if they were not hindered by throwing sand upon 



• This author was not acquainted with the true nature of this salt. Native natron (carbonate of 

 soda) is not pure, but generally contains an admixture of sea salt (muriate of soda) calcareous earth, 

 (carbonate of lime) and sand ; sometimes clay also. The purified natron is a compound of soda and 

 carbonic acid. 



•f- This red clammy substance, which colours both the water and the salt itself, appears from the 

 experiments of M. Berthollet not to be a mineral substance, but a vegeto-animal matter, susceptible of 

 combustion, during which it gives out ammoniacal vapours. 



+ There are six natron lakes in the desert or valley here mentioned. A description of them 

 by General Andreossy is inserted in the Memoires sur I'Egypte, torn. 1. The water of these lakes 

 analysed by M. Berthollet was found to contain sea salt (muriate of soda) mild mineral alkali (carbo- 

 nate of soda) and a little Glauber's salt, (sulphate of soda). See Observations sur le Natron par M. 

 Berthollet, in the last mentioned memoirs. 



§ That is (as the author afterwards remarks) when die water is evaporated to a certain degree by 

 the heat of the sun, a film forms on the surface, and the salt shoots into crystals. 



II This assertion respecting the virtues of natron (carbonate of soda) in calculous cases, is con- 

 firmed by the experience of modem practitioners. 



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