714 ZOOPHYTES. 



" The average from the sixteen species of corals is 2-523. 



" Colour. In general the colour of the specimens examined was white, or nearly so ; 

 but some of them, as Dendrophyllia nigrescens, and the blue Heliopora (H. cerulea) were 

 highly coloured. The colouring matter, in all cases, proved to be organic, and was gene- 

 rally due to some trace of the animal tissues. The highly-coloured ones, when powdered, 

 burned white, giving out, at a red heat, the odour of animal matter. The Heliopora dis- 

 solved in chlorohydric acid, without having its colour altered, and gave a light indigo- 

 blue solution. A drop of nitric acid, however, discharged this colour, and ammonia threw 

 it down as a brown precipitate. Heat immediately destroys it. It is, therefore, evident 

 that the colouring matter is entirely organic, and is in no way connected with the mineral 

 constitution of the coral. However, some corals have a slight ferruginous tint, from the 

 presence of a little peroxyd of iron, which will be seen to be an almost constant consti- 

 tuent, although in exceedingly small quantity. 



" Behaviour with reagents. All corals are rapidly dissolved in dilute chlorohydric, 

 nitric, or acetic acids, with brisk effervescence and escape of carbonic acid. The solution 

 is frequently coloured by organic matter, which sometimes renders it turbid. When the 

 powdered coral is treated with pure water, more or less of common salt and other soluble 

 saline matters, derived from the evaporation of sea water, are washed out, and this pre- 

 caution was found necessary to insure accurate results. 



"The solution of a coral in nitric acid is very soon blackened by a solution of nitrate of 

 silver, from the presence of organic matter. Ammonia, added to a solution in nitric .or 

 chlorohydric acid, with the least possible excess of acid, will generally produce an imme- 

 diate precipitate of granular ammonio-phosphate of magnesia, thus indicating the presence 

 of both magnesia and phosphoric acid. 



" Chloride of barium produces, with a chlorohydric solution, a granular, white precipitate, 

 which is nearly all redissolved in an excess of chlorohydric acid. (A small portion of 

 sulphate of barytes is generally formed in using this test, owing to the almost constant 

 presence of a small quantity of sulphate of lime in the corals.) 



" A portion, dissolved in nitric acid, and carefully neutralized, when treated with nitrate 

 of silver, will, on standing, deposit a considerable yellowish precipitate of phosphate of 

 silver, which is redissolved in ammonia and nitric acid. 



" Acetate of lead, added to a chlorohydric solution, produces a copious precipitate of 

 chloride of lead, which is not wholly redissolved by an excess of acetic acid, but is taken 

 up by nitric acid. These facts are a sufficient proof of the presence of phosphoric acid. 



" Lime-water, added to a solution of coral, either neutral or slightly acid, will produce 

 an immediate gelatinous precipitate of all the bases and acids which the coral can contain, 

 except, of course, the lime and solvent acid. Great care is needed in this operation to 

 prevent the formation of a carbonate of lime : the solution should have been recently 

 boiled, and the test applied while it is yet hot, the air being excluded ; and the precipitate 

 should be immediately collected on a filter and washed. If the precipitate by lime-water 

 be fused in a platinum capsule, with carbonate of soda, or carbonate of potassa in excess, 

 the phosphoric acid is all transferred to an equivalent portion of alkaline base, while the 

 lime or magnesia, or the base with which it was before united, will remain as a carbonate. 

 The usual tests, which have already been enumerated, will show the presence of the 

 phosphoric acid. 



"Thelime-u'ater test offers far the best means of separating from the lime (which exists 

 as a carbonate), all the other constituents of a coral, as these various substances are in 



