288 Dr. John T. Plummer on the 



another whose interstices were the twenty-fourth of an inch in 

 width ; and lastly, through gauze, by which a very fine dust 

 was obtained. This process yielded the following proportions of 

 pebbles, sand, and dust, in one thousand grains. 



Very coarse sand and pebbles, - 80 grs. 



Coarse sand, - - - 86 " 



Fine sand, - 125 " 



Dust, - - - 709 " 



Sixteen hundred grains of this dust thoroughly dried, were 

 heated to redness, to remove vegetable matter. The loss sus- 

 tained was 36 grs., or exactly 2.25 per cent. ; coinciding with 

 the result of a previous experiment on one fourth the quantity of 

 the powder, within .03 of a grain. Another quantity of nearly 

 800 grains lost but 1.02 per cent. Two hundred grains of it 

 were then fused with carbonate of soda, and dissolved in hy- 

 drochloric acid. The solution was evaporated, and the silica 

 separated by redissolving the residue in pure water. From the 

 aqueous solution, the alumina and iron were precipitated by 

 bicarbonate of soda and hydrochloric acid. A trace of manga- 

 nese was discovered in the clear liquid, by means of chlorine. 

 The lime was precipitated by oxalate of ammonia, and the 

 magnesia by ammonia and phosphate of soda. The presence 

 and quantity of potash, and of the sulphate and phosphate of 

 lime, were determined by separate processes ; the weight of the 

 crystals of alum formed by boiling 100 grains of the ignited 

 dust in sulphuric acid, enabled me to estimate the proportion of 

 potash, including the almost inappreciable quantity derived from 

 the incineration of the vegetable substances in the silt ; the di- 

 gestion in a large quantity of water, of several hundred grains of 

 the fine dry dust, yielded the sulphate of lime ; and the careful 

 evaporation of a solution in hydrochloric acid, and the addition 

 of pure water to the residue, left me an undissolved substance, 

 which I considered phosphate of lime, slightly tinged with iron. 

 These salts of lime I deducted from the oxalate of lime obtained 

 by the first experiment ; and having verified several parts of the 

 analysis by other methods, I think the following results may be 

 relied upon as correct. In 100 grs. of the thoroughly dried silt 

 dust, there are of 



