CHEMICAL COMPOSITION OF INCRUSTATIONS. 105 



grounds. The Mojave Indians are on the opposite bank of the river, and occasionally these 

 latter travel south along this plain to make incursions upon the peaceable Maricopas. 



Along its whole extent it is said to exhibit the same character — sterile where the soil is dr)', 

 fertile where it can be irrigated, and without timber tliroughout. 



Saline incrustations. — During the period of visit many of the small basin beds were dried 

 up, and presented a rippled sandy surface, easily impressed with the foot, but yet sufficiently 

 coherent to resist the action of light winds. Upon the surface a dry whitish efflorescence 

 was spread, which tasted alkaline and unpleasantly. Two such efflorescent incrustations were 

 collected — one at a spot on the Mojave river known as Navajo camp, (Camp 3 ;) the other was 

 collected from the surface of the dry playa called Soda lake. Portions of each of these were 

 subjected to chemical examination, with the following results : 



Incrustation of dry playa called Soda lake. — In mammillary bunches and botryoidal masses, 

 efflorescent, readily crumbling uuder the finger, dull white externally, purer white and serai- 

 crystalline internally ; readily and completely soluble in cold water. Solution is colorless and 

 transjaarent, and possesses a very faint alkaline reaction. 



While crystallizing iinder the microscope, two forms of crystals are observable — needle prisms 

 and cubes. 



The solution tested with a barium salt gave a light precipitate, and a copious white with a 

 silver solution, which is soluble in ammonia. 



The solution was not aifected by solutions of oxalate of ammonia or carbonate of soda, and 

 did not eifervesce on the addition of an acid. 



The salt mass fused readily before the blow pipe and gave a deep yellow tinge to the flame. 

 From the foregoing it is evident that both sulphuric acid and chlorine are j^resent, with the base 

 sodium, and the crystalizations shows that only two salts are contained in the solution. The 

 cubes are therefore chloride of sodium and the needles sulphate of soda. There is a mere trace 

 of carbonate of soda, and not any lime salt present. The solution on standing deposits traces 

 of silica. The amount of sulphuric acid present was determined in the usual way, and calcu- 

 lated for sulphate of soda ; the difference was set down as chloride of sodium. The mass is not 

 homogeneous ; the centre of the nucleus containing the greatest amount of chloride, while the 

 sulphate was round the periphery of the crust. Thus, one portion differed a little centesimally 

 from another ; but the following is an average of these estimations : 



Chloride of sodium 85. 



Sulphate of soda 14.6 



Carbonate of soda, silica .4 



100.0 parts. 



The very small quantity of carbonate present in this crust is singular, since an alkaline car- 

 bonate exists in the well waters at the margin of the playa. The water of the wells at the 

 bivouac distintly effervesced and was very unpleasantly alkaline to the taste ; the crust was taken 

 one mile out in the middle of the playa which may account for its small quantity of carbonate. 



Incrustation of soil at Navajo Camp. — An earthy powder of a light yellow brown color, and 



without trace of crystallization, of a dull white color, discolored by the surface soil ; efflorescent, 



partially soluble in water ; solution transparent, of an amber tint, owing to vegetable matter ; 



highly alkaline reaction to test paper ; strong effervescence on addition of nitric acid to solution. 



14 U 



