1888.] Messrs Irvine and Young on Carbonate of Lime. 319 
(prepared by passing carbonic acid into lime water) is added to sea 
water to saturation ; the perfectly clear solution, on standing for some 
time, depositing a considerable proportion of crystallised carbonate 
of lime, which it had, in the amorphous state, before dissolved. It 
is due to this molecular change that coral deposits, shells, or cal- 
careous plants are able to accumulate in the ocean, ultimately to form 
beds of limestone rocks ; for if such a structural change did not take 
place, the secreted amorphous carbonate would be redissolved in the 
seawater from which it was extracted. In this case also the ammoniacal 
salts produced by the decomposition of nitrogenous organic matter 
will check the solvent action of sea water, and will, moreover, tend 
to add to the accumulation of carbonate of lime, by precipitating 
the lime existing in solution in the sea water surrounding such beds. 
Besides, other influences are at work in preserving these deposits, 
such as the silting up of coral or shell debris with mud and sand, 
a good example of which is given in a letter from Mr David Wilson 
Barker, which appeared in Nature, vol. xxxvii. p. 604 : — “ Large 
masses of coral, much altered by the rains, weather (or partly 
dissolved), are to be found on the plains of Massowah, which extend 
3 or 4 miles in south-west, west, and north-west directions. They 
show unmistakable signs of the undermining action of the sea, 
which can still be seen going on around the coast and harbour. At 
Mokulla, at a depth of 20 feet, I observed masses of coral (Aperosa) 
almost perfect in shape, covered up with alluvium.” 
There is also the protective action of vegetable matter in the form 
of sea-weed ; and lastly, in the case of coral reefs, the living, grow- 
ing structure itself, which, of course, secretes more carbonate of lime 
than the solvent action of sea water removes. 
The sea water we employed in these experiments was procured 
from the German Ocean, about twenty miles from land, of sp. 
gr. about 1*026. 
The following method of estimating the amount of carbonate of 
lime dissolved by sea water was adopted : — The total amount of 
calcium salts present in sea water was estimated by precipitation, 
and weighed as caustic lime. The coral or other substance was 
exposed to the action of a fixed amount of sea water for a given 
time and at certain temperatures. Many safeguards had to be 
adopted — for example, the careful measurement of the water em- 
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