COMPOSITION OF CORAL. 75 



consist almost wholly of carbonate of lime, the same ingredient 

 which constitutes ordinary limestone. In 100 parts, 95 to 98 

 parts are of this constituent; of the remainder, there are i^ 

 to 4 parts of organic matter, and some earthy ingredients 

 amounting usually to less than i per cent. These earthy 

 ingredients are phosphate of lime, with sometimes a trace of 

 silic;a. A trace of fluorine also has been observed. 



S. P. Sharpies found the following constitution for the 

 species below namec^ {Afji. Jou?\ Sci., III., i. 168). 



CARBONATE 

 OF LIME. 



Oculina arbuscula, N. Car. . . . 95 '37 . 



Manicina areolata, Florida . . . 96'54 . 



Agaricia agaricites 9773 • 



Siderastrtea radians 97*30 . 



Madrepora cervicornis 98'07 . 



Madrepora palmata 97 "19 • 



Forchhammer found 2*1 per cent, of magnesia in Corallium 

 rubriim, and 6*36 in Isis hippuris. 



The sea-water, and the ordinary food of the polyps, are 

 evidently the sources from which the ingredients of coral are 

 obtained. The same powers of elaboration which exist in 

 other animals belong to polyps ; for this function, as has been 

 remarked, is the lowest attribute of vitality. Neither is it at 

 all necessary to inquire whether the lime in sea-water exists as 

 carbonate, or sulphate, or whether chloride of calcium takes 

 the place of these. The powers of life may make from the 

 elements present whatever results the functions of the animal 

 require. 



The proportion of lime salts which occurs in the water ot 

 the ocean is about -^V to ^^ of all the ingredients in solution. 

 The lime is mainly in the state of sulphate. Bischof states 

 that the proportion of salts of all kinds in sea-water averages 

 3-527 per cent.; and in 100 parts of this, 7579 are chloride 

 of sodium, 9-i6 chloride of magnesium, 3*66 chloride of 

 potassium, I'lS bromide of sodium, 4-62 sulphate of lime or 



