y 
280 Native Nitrate of. Soda. 
and chloride of sodium, in large beds, exposed on 
their upper surfaces freely to the air. "The whole 
surface of the pampa is made up of saline matter, 
mixed with sand composed of water worn shells and 
detritus of trachytic rocks, presenting an area of 
many square miles of variable depth. Below the 
surface, in several places, is found the fossil wood, 
the trees being entire, and generally inclined toward 
the southwest. Numerous volcanoes exist in the 
Andes, between which and the pampa a range of 
low hills intervenes, marking apparently the border 
of the surface, once covered by alake. These speci- 
mens were obtained by Mr. John H. Blake, of Bos- 
ton, to whom I am indebted for a description of the 
locality, which will soon be published. 
Roxbury Laboratory, 17th July, 1838, 
EXTRACT FROM THE LETTER. 
“The nitrate of soda contains a salt of chlorine and iodine 
united. This is proved by moistening a few grains of the yel- 
low part of a mass with water, and rubbing it on starch paper ; 
if free iodine were present, a purple or blue color would be 
produced. Weak sulphuric acid, added to the moistened mass, 
gives it the power of thus altering the starch, and, as bromine 
is not present, no other known body can produce that effect. 
If such a mixture be distilled, chloride of iodine passes over 
into the recipient. That iodate of soda is present, is proved by 
the fact, that the saline matter, which is mixed with the nitrate 
of chlorine, in a solution of starch in sulphuric acid. When 
heated with carbon, it deflagrates feebly, and the residue, dis- 
Solved in water, instantly renders a solution of starch in sul- 
uric acid blue, if chlorine is present, Magnesia is always 
n the specimens.” 
