86 Proceedings of Royal Society of Edinburgh. [sess. 
Experiment III. An artificial sea water similar to the above 
(II.), absolutely free from carbonate of lime, was neutral at first, 
but after the introduction of living crabs became at first slightly 
acid, and then, after a time, distinctly alkaline in character. This 
was found to be due to uric acid, urea, and other effete products 
thrown into the water by the crabs, and to their subsequent decom- 
position, with the formation of carbonate of ammonia, and ultimately 
of carbonate of lime. In one of the tanks the alkalinity was equal 
to the production of about 45 36 grammes of carbonate of lime — 
this representing the amount of that body formed in twelve months 
through the agency of four small crabs, weighing in all about 
90 -7 2 grammes, and whose exo-skeletons contained only about 
5T84 grammes of carbonate of lime. 
Experiment IY. The following experiments were conducted with 
the view of throwing some light on the above changes. Three litres 
of sea water and 750 c.c. of urine were mixed and kept exposed to 
the air at a temperature ranging from 60° to 80° Fahr. What was 
lost by evaporation was made up by the addition of pure water. 
This solution was at first acid ; after a few days it became neutral, 
and later, as decomposition of the urine advanced, it became strongly 
alkaline. On heating a portion of the solution, ammonia was given 
off, so that the alkalinity was evidently due to the formation of 
ammonia. After seven days a bulky flocculent precipitate was 
thrown down, which on analysis consisted of organic matter, double 
phosphate of magnesia and ammonia, together with a small quantity 
of carbonate of lime, as shown by the following analysis : — 
Precipitate after Seven Days. 
Water and organic matter containing ammonia, 1 
31-81 
7*38 grains, . . . . . . J 
Carbonate of lime, ...... 
4-85 
Phosphate of magnesia and ammonia, 
51-10 
Phosphate of lime, ...... 
12-24 
100-00 
After other ten days, during which time the liquid, filtered from 
the above precipitate, was exposed under the same conditions, a 
further precipitate was thrown down, differing from the first in that 
