182 BULLETIN OF THE BUSSEY INSTITUTION. 
employed for the analyses recorded in the table. The methods and 
results were as follows :— 
A weighed quantity of powdered oyster-shells was digested with cold, 
highly-dilute chlorhydric acid until the whole of the carbonate of lime 
was dissolved ; the insoluble organic matter was washed, dried, and 
weighed ; and the amount of nitrogen in this organic matter was de- 
termined by combustion with soda-lime. In two experiments, there 
were found 1.04% and 1.30% of organic matter, respectively. The 
nitrogen amounted to 6.37% of the dry organic matter, or to 0.066% 
and 0.069% of the original dry shell. : 
In order to avoid the risk (already noticed in the note on page 178) 
of failing to get the whole of the nitrogen when the powdered shells are 
ignited with soda-lime directly, weighed quantities of powdered oyster- 
shell were treated with acid enough to completely decompose the lime- 
salt, and the excess of acid was neutralized with soda-lime. The dry 
powder thus obtained was mixed with more soda-lime, and the nitrogen 
estimated by combustion of the mixture in the usual way. By operat- 
ing in this manner, there was found in the dry oyster-shell 0.12% of 
nitrogen in one instance, and 0.092% in a second trial. All of which 
goes to show that the amount of nitrogen in the oyster-shells examined 
in this laboratory is really very small, as was stated in the table, and 
by no means so large as was to have been inferred from the statement 
of Boussingault and Payen. 
Other experiments still were made, to determine, more precisely than 
had been done before, how much the dry powdered shells lost when their 
organic matter was destroyed by the method of ignition. To this end, 
two separate portions of the dried powder were thoroughly roasted, the 
residues were moistened with a solution of carbonate of ammonia, in order 
to replace any carbonic acid that might have been driven off from the lime 
during the calcination, and then dried and weighed; and the process was 
repeated until the weight of the matter in the crucible remained constant. 
There was found in this way, in one not very satisfactory experiment, 
2.83%, and, in another and better trial, 3.61% of ‘‘ loss by ignition.”’ It 
is hard to believe, however, that the whole of this loss by ignition is really 
organic matter. Probably a considerable part of the loss is mere water, 
that was retained so forcibly by the shell that it failed of being driven off 
at the temperature of 110°. It will be noticed that the amount of the loss 
by ignition is very much larger than the amount of organic matter that 
was found directly by treating the shell with an acid, as was just now 
stated; and the discordance between the two results is perhaps even more 
