is 
ms, 
“4 
x 
192 Mr. Silliman, Jr. on the Composition of Corals. 
The average from the sixteen species of corals is 2°523. 
Color.—In general the color of the specimens examined was 
white, or nearly so ; but some of them, as the Dendrophyllia nigres- 
cens, and blue Heliopora (H. cerulea) were highly colored. The 
coloring matter, in all cases, proved to be organic, and was usu- 
ally due to some trace of the animal tissues. ‘The highly col- 
ored ones, when powdered, burnt white, giving out, at a red heat, 
the odor of animal matter. The Heliopora dissolved in chloro- 
hydric acid, without having its color altered, and gave a light 
indigo-blue solution. A drop of nitric acid, however, discharged 
this color, and ammonia threw it down as a brown precipitate. 
Heat immediately destroys it. It is, therefore, evident that the 
coloring 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 con- 
stituent, although in exceedingly small quantity. 
Behavior 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 colored 
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 precaution 
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 
aci 
Chloride of barium produces, with a chlorohydric solution, @ 
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 
- 
foe TR as 
