BULLETIN OF THE BUSSEY INSTITUTION. 181 
Silliman * found less than one per cent of magnesia in his analyses of 
recent corals. Phipson t found 0.139% of magnesia in the shells of the 
common cockle of Europe. 
There are several noteworthy differences as to the proportion of 
nitrogen contained in the different shells, which undoubtedly depend 
not so much upon differences in the amounts of organic matter in the 
different shells as upon the presence in the organic matter of a larger 
or smaller proportion of nitrogenized compounds, It may possibly be 
true, moreover, that different kinds of nitrogenized compounds occur in 
different kinds of shells. A certain amount of attention has been called 
to this question already by the conflicting results obtained by various 
chemists who have examined the organic matter in shells; and it is to 
be understood that the results given above do but emphasize peculiari- 
ties which had been noticed before. Thus, in the case of the fresh 
shells of the small mussel, No, viii. of the table, it will be seen that the 
proportion of nitrogen is unusually high, both when the nitrogen is re- 
ferred to the dry shells, of which it constitutes 0.28%, and when it is 
referred to the organic matter (“loss by ignition’) in the shell, of which 
the nitrogen constitutes a little more than 9%. It would seem to be 
evident, on comparing this result with those obtained from the other 
sea-shells, that the mussel-shell must contain an unusually large pro- 
portion of the highly nitrogenized substance known as conchiolin, which 
has been found by Fremy ¢ and Schlossberger § in some kinds of sea- 
shells and in coral. The organic matter in the oyster-shell, on the 
other hand, though by no means entirely free from nitrogen, evidently 
contains comparatively little conchiolin. 
Since the percentage of nitrogen (0.083) in the dried oyster-shell 
of the table differs very decidedly from the amount given by Boussin- 
gault and Payen || some years since, I have been at pains to verify 
the observation, and have had other analyses made for the purpose of 
determining the amount of organic matter in the oyster-shell, and 
the nitrogen in this organic matter, as well as new estimations of 
nitrogen in the shell itself, by a process somewhat different from that 
* “ American Journal of Science,” 1848, 6. 269. 
t “ Report British Association,” 1859, p. 77. 
t “Annales de Chimie et de Physique,” 1855, 43. 96. 
§ “ Annalen der Chemie und Pharmacie,” 1856, 98. 103. 
|| “Annales de Chimie et de Physique,” 1841, 3. 103. They found 0.40 % of 
nitrogen in the dried shell, or 0.32 % in the fresh, undried shell. 
