Chemical Composition of the Calcareous Corals, 245 



Nine of the above species, of which there was the largest 

 quantity on hand, were selected for a minute determination 

 of each ingredient, while of the others, only the proportion 

 of carbonate of lime and animal matter to the other in- 

 gredients, was determined. The following are the nine 

 selected : — 



I. Porites favosa (No. 1), Sandwich Islands. 

 II. Madrepora palmata (No. 9), West Indies. 



III. Madrepora spicifera (No. 10), Ceylon. 



IV. Madrepora prolifera (No. 11), Bermuda. 

 V. Madrepora plantaginea (No 12), Ceylon. 



VI. Pocillopora ligulata (No. 22), Sandwich Islands. 

 VII. Meandrina phrygia (No. 28), Ceylon. 



VIII. Astrsea orion (No. 29), Ceylon. 

 IX. Astr^ea (No. 30, p. 721, pi. 13, fig, 15.) 



A few remarks are added upon some of their physical cha- 

 racters, before giving the mode and results of analysis. 



Hardness. — All the various corals examined were superior 

 in hardness to calcareous spar or common marble, and not 

 inferior to arragonite ; while some were as hard as apatite 

 or crystallized phosphate of lime ; or, according to the scale 

 used by mineralogists, the usual hardness will be expressed 

 by 4, though occasionally as high as 5. Using an iron mor- 

 tar in the earliest trials, the iron pestle was roughened and 

 cut under the resistance of the angular masses of coral, to a 

 degree quite remarkable, considering the nature of the sub- 

 stance operated on. So much iron was communicated to the 

 powder from this source, that recourse was had to a mortar 

 of porcelain, and even this was not proof against wear, the 

 porcelain pestle being pitted by the repeated blows. The 

 more porous species were crushed, of course, with less diffi- 

 culty ; and this was especially the case with the species of 

 porites.* 



* On this subject, Mr Dana remarks, p. 711 : — " The hardness of 

 these coral secretions, which is much above that of common carbonate 

 of lime, as stated by Mr Silliraan, is not fully explained by the pecuUar 

 chemical composition detected by this chemist. We suggest, as one 

 cause, that the calcareous portion may have, in its intimate texture, the 

 structure of arragonite, or prismatic carbonate of lime, instead of that 



