BULLETIN OF THE BUSSEY INSTITUTION. 187 
lime has no such marked influence upon its solubility as the presence of 
the enveloping membrane of organic matter in the shells was shown by 
the fact that 1,000 parts of water, saturated with carbonic acid, dissolved 
0.42 parts of powdered cale-spar; ¢.¢., three times as much as was dissolved 
from the powdered pearly portion of the shell. Quenstedt had previously 
remarked that shells taken from heaps dating from prehistoric times effer- 
vesce more strongly than fresh shells when treated with dilute muriatic 
acid; and that, while the fresh shells yield with the acid a gelatinous 
mass, having the form of the shell, the old shells leave no such gelatinous 
residue. 
In this connection, some experiments of Sorby * have a certain interest. 
They were made for the purpose of determining why it is that several] 
kinds of shells, such as those of oysters or limpets, are more frequently 
met with in a fossil state than other kinds, such as cockle-shells, for 
example. According to Sorby, it is a fact of common observation that 
certain kinds of fossil-shells are found to have lost their organic structure, 
or to have been entirely removed from the same beds in which other kinds 
remain almost in their original state. Most univalve shells — such bivalve 
shells as Trigonie, and the inner layer of Avicule and Spondyli— are 
often altered or removed though their outer layer, and the entire shells of 
Ostrecee and Brachiopoda, are well preserved. He finds by experiment that 
this difference in durability is due to original differences in the condition 
of the caleareous matter of the shells; and that, other conditions being the 
same, shells which were composed of calcite are preserved, while those 
composed of arragonite have been altered. 
Sorby seeks to explain the phenomenon by supposing that it depends on 
the fact of the particles of arragonite being in a state of unstable equilib- 
rium. When prepared artificially, arragonite has a great tendency to pass 
into calcite; and, if this change took place in shells, their organic structure 
would be very apt to be destroyed, and the solution of the calcareous matter 
in so far promoted. 
It is manifest that if, by expelling their carbonic acid, when the 
shells are burnt to quick-lime, nearly half the weight of the original dry 
shells is lost, a given weight of shell-lime must contain nearly twice as 
much phosphoric acid and potash and magnesia as is contained in an 
equal weight of shells, such as those from which the quick-lime was pre- 
pared. Thus, while a ton of oyster-shells contains 1} lbs. of phosphoric 
acid and three-fourths of a pound of potash, — as will be shown directly, 
—a ton of oyster-shell lime might contain about 24 lbs. of phosphoric 
acid and 14 lbs. of potash. All this consists perfectly with the results 
* “Report of the British Association for the Advancement of Science,” 1862, 
p. 95 of the abstracts. See also Pengelly, “ Quarterly Journal of Science,” 1871, 
8. 828. 
