the native Carbonate of Soda from Fezxan. 329 



terwards boiled up into thin crystallized cakes* only that the 

 crystals are much smaller, and in a manner that cannot be ea- 

 sily imitated by art ; for when this salt is dissolved and eva- 

 porated to a pellicle, and left to crystallize, it always shoots 

 into crystals resembling those of glauber-salt."' 



Another account was published by Mr Bragge,* Swedish 

 eonsul at Tripoli ; it is from his notice that more generally the 

 indications in the works on mineralogy are taken. According 

 to Mr Bragge, the " native country of this soda, there called 

 Trona, is the province Sukena, two journeys distant from Fez- 

 zan. It is found at the foot of a rock mountain, upon the 

 surface of the earth, at no greater depth than that of an inch, 

 and as to breadth mostly that of the back of a knife's blade. 

 It occurs always crystallized ; on the fracture it exhibits con- 

 crete, oblong, parallel, and sometimes striated crystals ; thus 

 resembling crude or unburnt gypsum." -f- He states, more- 

 over, that it is found twenty-eight days journey from the sea 

 coast, where the salt mines ai'e, and that it is not contaminated 

 with common salt. Large quantities are exported to the coun- 

 try of the Negroes and to Egypt, besides 50 tons annually 

 which are brought to Tripoli. 



The description given by Klaproth himself is confined to the 

 statement that he examined *' crystalline incrustations, from 

 one-third to half an inch thick, of accumulated parallel plates, 

 standing on their smaller edges, and of a lamellar striated tex- 

 ture." 



The systematic works on Mineralogy contain little farther 

 information on this subject. Some have distinguished Troisa 

 as a particular sub-species, but the greater part include it in 

 one species with the hemi-prismatic natron-salt, according to 

 the principle that they both essentially consist of carbonate of 

 soda. 



From the treatises on geography we learn that there is a parti- 

 cular district of Fczzan, called Mendrah, with a hard and barren 

 soil, but which has a commercial importance for the quantity 

 of trona, a species of fossil alkali, which floats on the surface, 



' Tetemk. Acad. Hanillingar, 1773, ]). 1 10. 

 t Kl.iprotli's Essays, vol. ii. p. 63. 



