Exper'imtnls an4 Obfervations en Shell and Bane. 505 



ditlon of acetlte of lead ; and having thus proved the prefence of phofphoric acid, I fatu- 

 rated the nitric folutions with pure ammoniac, by which a quantity of phofphate of lime 

 was obtained, much inferior however in quantity to the carbonate of lime, which was 

 afterwards precipitated by carbonate of ammoniac. 



The compofition of tlie cruft of tlie echinus is therefore different from' that of marine 

 (hells i and by the relative proportions and nature of the ingredients, it approaches mod 

 nearly to the fhells of the eggs of birds ; which in like manner confift of carbonate, with 

 a fmall proportion of phofphate of lime cemented by gluten. 



It remained now to examine the compofition of thofe fubftances which are decidedly 

 called cruftaceous ; but previous to this fome experiments were made on the afterias, or 

 ftar fifh, of which I took the fpecies commonly found on our coafts, and known by the 

 popular name of five fingers (afterias rubens.) 



The afterias is thus defcribed by Linnreus. " Corpus depreflum, fubtus fulcatum ; 

 *' crufta coriacea, tentaculis muricata*." 



When the afterias was immerfed in the acids, a confiderable effervefcence was pro- 

 duced, and a thin external ftratum was diflblved ; after which it remained in a perfeflly 

 coriaceous ftate, and complete in refpedl to the original figure. 



The diflblved portion being examined by the ufual precipitants, proved to be carbonate 

 of lime, without any mixture of phofphate ; but in another fpecies of the afterias, which had 

 twelve rays (afterias pappofa,) I difcovered a fmall quantity of phofphate of lime. I am 

 therefore induced to fufpeft that in the difl^erent fpecies of the afterias, nature makes an im- 

 perfeft attempt to form (hell on fome, and a cruftaceous coating on others ; and that a 

 feries of gradations is thus formed between the teftaceous, the cruftaceous, and the 

 coriaceous marine animals. 



It was now requifite to afcertain if phofphate of lime is a component part of the fubftance 

 which covers, the cruftaceous marine, or aquatic animals, fuch as the crab, lobfter, prawn, 

 and crayfilh . 



Pieces of this fubftance, taken from various parts of thofe animals, was at different times 

 Immerfed in acetous and in diluted nitric acid ; thofe which had been placed in the diluted 

 nitric acid produced a moderate effervefcence, and in a fhort time were found tobe foft and 

 elaftic, of a yellowifh white colour, and like a cartilage, which retained the original figure. 



The fame effects were produced by acetous acid, but in a lefs degree ; in the latter cafe 

 alfo a colouring matter remained, and was foluble in alcohol. 



All the folutions, both acetous and nitric, afforded carbonate and phofphate of lime, 

 although the former was in the largeft proportion. 



There is reafon to conclude, therefore, that phofphate of lime, mingled with the car- 

 bonate, is a chemical charafteriftic which diftinguifhes the cruftaceous from the teftaceous 

 fubftances i and that the principal difference in the qualities of each, when complcat, is 



• Syftema Natura. Ed, Graelin. p. 3160. ■ 



caufed 



