so 
194. Mr. Silliman, Jr. on the Composition of Corals. 
trived in part from the late researches of von Rammelsberg, on 
the estimation of phosphoric acid, and partly from the labors of 
Rose and Berzelius, adapting the method to the requirements of 
the particular problem before us. 
A. The lime-water precipitate, after ignition, is weighed and 
then digested in fine powder in cold chlorohydric acid; it slowly 
dissolves, leaving a white flocculent powder. ‘This collected and 
washed, will be found to be silica. It is harsh and gritty be- 
tween the teeth, is not taken up by long digestion in strong acids, 
dissolves in a solution of caustic potassa, and before the blowpipe 
forms a hard colorless glass with carbonate of soda, dissolving in 
this reagent with effervescence. 
B. The solution in chlorohydric acid is supersaturated with 
caustic ammonia, and boiled; a gelatinous precipitate separates, 
which is usually colored by iron, and by its characters indicates 
the presence of alumina. This precipitate contains the phos- 
phoric and other acids, and the bases therewith combined. It is 
collected, and the filtrate therefrom (C) is examined for dime and 
magnesia, both of which are usually present. 
D. The precipitate by ammonia (B) is next made into a thick . 
paste with strong sulphuric acid, in a small vessel of platina. A 
plate of glass coated with wax and written on, is placed over the 
crucible ; and heat being applied, hydrofluoric acid escapes, and 
attacking the glass, leaves a permanent record of its presence. 
I have never failed to obtain evidence of the presence of flu- 
orine in any coral which has been subjected to the test. Gen- 
erally, exposure for one minute will etch the glass most decidedly ; 
and one experiment will suffice to mark distinctly several pieces 
of glass. By this plan of analysis the quantity of fluorine cannot 
be estimated, and it must be judged of either by the loss or by 
the deficiency of acids to satisfy all the bases formed. The con- 
stant association of phosphoric acid and fluorine, renders it ad- 
visable, in compounds in nature, where one of these elements is 
found, to search for the other. 
E. After the sulphuric acid has been digested on (D) long 
enough to convert all the bases present into sulphates, a portion 
of bisulphate of potash or caustic potash is added, and a little 
water, to dissolve it; to this, a very large quantity of alcohol, of 
a specific gravity of about -860, is added, and the whole is allowed 
to stand for some hours; during which the double sulphates of 
