Chemical Composition of the Calcareous Corals. 249 



and gritty between the teeth, is not taken up by long di- 

 gestion in strong acids, dissolves in a solution of caustic 

 potassa, and before the blowpipe forms a hard colourless 

 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 coloured by iron, and by its cha- 

 racters indicates the presence of alumina. This precipitate 

 contains the phosphoric and other acids, and the bases there- 

 with combined. It is collected, and the filtrate therefrom 

 (C) is examined for lime 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 

 pliatina. A plate of glass coated with wax and written on, 

 is placed over the crucible ; and heat being applied, hydro- 

 fluoric acid escapes, and, attacking the glass, leaves a per- 

 manent record of its presence. I have never failed to obtain 

 evidence of the presence of fluorine in any coral which has 

 been subjected to the test. Generally, exposure for one 

 minute will etch the glass most decidedly ; and one experi- 

 ment 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 

 constant association of phosphoric acid and fluorine, renders 

 it advisable, 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 por- 

 tion of bisulphate of potash or caustic potash is added, and a 

 little water, to dissolve it ; to this, a vei'y 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 potassa, alumina and iron, crystallize out, 

 while any lime previously combined is separated as sulphate ; 

 and in the solution we must look for the phosphoric acid and 



VOL. XL. NO. LXXX. — APRIL 1846. R 



