710 PHILOSOPHICAL TRANSACTIONS. [ANNO 1800. 



effect. Carbonate of ammonia precipitated a large quantity of carbonate of lime. 

 Some of the corallina opuntia was then exposed to a low red heat, in a crucible; 

 it emitted a smell of burnt horn, and in great measure retained its shape, evidently 

 from the calcareous coating. The burnt coralline, being dissolved in dilute nitric 

 acid, deposited some animal coal. The clear solution afforded, by pure ammonia 

 a very slight precipitate of phosphate of lime; after which, the carbonate of lime 

 was precipitated as before. This coralline, when treated with boiling water, like 

 the flustra foliacea, did not discolour it; neither was the water changed by infusion 

 of oak bark ; but nitro-muriate of tin produced a faint white cloud. 



Isis ochracea. — When this isis was immersed in dilute nitric acid, a considerable 

 effervescence was produced ; and, in proportion as the calcareous substance was dis- 

 solved, the red colouring matter was deposited, in the state of a fine red powder*. 

 When the effervescence had ceased, which was after about 3 hours, a yellowish 

 membrane remained, which completely retained the original figure of the isis. The 

 solution, being filtrated, was saturated with pure ammonia by which a slight pre- 

 cipitate of phosphate of lime was separated. A large quantity of carbonate of 

 lime was afterwards precipitated, by solution of carbonate of potash. 



Part of a branch of this isis was put into a crucible heated to a low red heat. A 

 great quantity of smoke was emitted, which had the smell of burnt horn; and 

 after a few minutes the branch separated at the knotty joints, into as many pieces 

 as there were joints in the branch. These joints had all the characters of coral; 

 but the whole of the membrane which had invested them, as well as the knotted 

 protuberances by which they had been connected, were destroyed, by being con- 

 verted into coal. From this circumstance, I was desirous to examine the internal 

 structure of the membranaceous part, out of which these joints of coral had been 

 dissolved by acids. 



I took, therefore, the membranaceous substance which remained after the first 

 experiment, and which retained the complete figure of the isis. This substance 

 being opened longitudinally, exhibited a series of cavities, corresponding in form 

 with the coralline joints, and so situated, that each of these cavities extended from 

 one bulb or knot nearly to the next, throughout the whole of the branch. The 

 coralline joints, when viewed separately, appeared smaller in the middle than at 

 the ends, which were terminated by obtuse cones. In the branch these joints 

 were so placed, that the extremities or' cones were opposed point to point ; but 

 were prevented from immediate contact, by a gristly substance, which filled, and 

 indeed principally formed in the branch, the knot or bulb of each joint, and was 

 interposed between the cones of the coralline substance, like the common carti- 

 lages of the articulations. 



From this construction it appears, that the isis is capable of great flexibility 



• This colouring substance was not dissolved, nor changed, when nitric or muriatic acid was poured 

 on it. It appears therefore to be very different from the tinging matter of the tubipora musica, or that 

 ©f the Gorgonia nobilis.— -Orig. 



