L ii'78 ] 



XLIII. Memoir on the Urao {Carbonate of Soda). By Messrs. 

 Mariano de Rivero and J. B. Boussingault *. 



nnO the south-west of Merida, and at one day's journey from 

 -*- tliis city, in the direction of La Grita, is a small Indian 

 village, called Lagunillas, on account of its being situated at 

 a short distance from a lake, whence the aborigines have ex- 

 tracted for a great number of years past a kind of salt called 

 Urao. 



The lake is about 3281 feet long and 820 wide. Its greatest 

 depth is not quite ten feet. It is situated in a clayey soil con- 

 taining large fragments of a secondary freestone. By a baro- 

 metrical obsenation we have made, it appears to be 3323*65 

 feet above the level of the sea. In order to obtain the ?irao, 

 tlie Indians make under the water an excavation of several yards 

 in extent, in which they place a pole, from It to 16 feet 

 long, the top of which projects above the water. This being 

 done, an Indian leaning on the first pole directs another to- 

 wards the bed of salt at a certain angle. On this pole a second 

 Indian immediately slides down, dives, and after a few minutes 

 spent under the water returns with some fragments of the salt. 

 Accorduig to the information we have received, there is pre- 

 vious to reaching the tirao, the bed of which is not very thick, 

 about a yard of mud and a bed containing many crystals of 

 carbonate of lime. The water of the lake is but slightly sa- 

 line, and animals drink it with avidity. 



The wao is crystallized in prismatic needles which appear to 

 diverge from a common centre ; it has a glassy aspect ; its 

 hardness is rather less than that of carbonate of lime ; its taste 

 alkaline, and similar to that of carbonate of soda ; it does not 

 effloresce on exposure to the air. We pass over the details 

 of the analysis, and only give the results : 



Carbonic acid 0-3900 

 Soda 0-4122 



Water 0-1880 



Foreign substances and loss 0-0098 

 This salt therefore contains more carbonic acid than the 

 carbonate, and less than the bi-carbonate. The carbonate of 

 soda called Tronn, analysed by Klaproth, and which came 

 from the province of Sukena, near Fezzan in Africa, has much 

 analogy with the icrao. The following are the results obtained 

 from it by the chemist of Berlin, 



Carbonic acid 0'3900 



Soda 0-3800 



Water 0-2300 



* From Annaks de Chimie, torn. xxix. p. 110; originally published in 

 Spanish, at Bogota. 



The 



