June 12, 1890] 



NATURE 



165 



The quantity of carbonate of lime normally present in sea- 

 water is exceedingly small ; and the opinion hitherto held seems 

 to have been that lime-secreting organisms must pump enormous 

 quantities of sea-water through their bodies in order to be able 

 to separate out a sufficient quantity to form their shells and 

 skeletons. 



Bischoff, in his "Chemical and Physical Geology," vol. i. 

 p. 180, estimates that oysters in this way have to deal with an 

 amount of sea-water equal to from 30,000 to 75,000 times the 

 weight of their shells. It seems more probable that the re- 

 actions indicated by our experiments render the whole lime salts 

 in sea- water available for coral polyps to build up their structures. 

 In polyps, which unlike the higher animals have no true cir- 

 culatory system, and where the animal is immersed in sea-water, 

 it is hardly possible to account for the enormous secretion of 

 carbonate of lime in the manner indicated by Bischoflf ; but if 

 the conclusion we have arrived at be correct, and such animals, 

 in place of secreting urea, secrete carbonate of ammonia, then 

 we have a perfectly reasonable explanation of the phenomenon 

 of coral formation. 



As a laboratory experiment, when carbonate of ammonia is 

 added to sea-water, the greater proportion of the calcium in 

 solution is after a time thrown down as carbonate of lime ; 

 whilst the magnesium salts reaiain in solution. So that if the 

 reaction above indicated be that which takes place in sea-water, 

 then to this circumstance may be due the fact that carbonate of 

 magnesia is almost wholly absent from coral reefs and deep sea 

 ca'careous formations. 



That the amount of nitrogenous organic matter in a state of 

 suspension and solution must be enormous will appear evident 

 when it is remembered that the floor of the ocean, almost 

 throughout its whole extent, is covered with living animals ; 

 that the surface of the sea and shallow waters off the coasts are 

 crowded with plants and animals down to a depth of several 

 hundred fathoms. (The Challenger experiments have shown 

 that some species of animals flourish in the intermediate depths 

 of ocean water from the surface to the bottom.) The waste 

 products arising from the functional activity of these organisms, 

 and the nitrogenous products arising from the decomposition of 

 their dead bodies, must work continual changes on the internal 

 constitution of sea-water salts, varying according to their amount, 

 the temperature, the sunlight, and other conditions. It has been 

 shown that ammoniacal salts are to be found everywhere in the 

 ocean, but much more abundantly in warm tropical waters than 

 in colder seas — a result no doubt due to the rapid decomposition 

 of the nitrogenous organic matter present at a high temperature, 

 and its retardation in colder water. The ammonia of the air, 

 and all nitrogenous substances carried from the land to the sea, 

 must also effect changes in the internal constitution of sea- 

 water. Indeed, the peculiar pelagic fauna and flora met with 

 in all regions of the ocean, where it is affected by river and 

 coast waters, are as different in relation with the internal con- 

 stitution of the sea-water salts as with the lower salinity which 

 prevails in these circumstances. 



It is well known that organic substances in the presence of 

 alkaline and earthy sulphates become oxidized at the expense of 

 the oxygen of these salts, with the production of carbonic and 

 hydrosulphuric acids, the latter on oxidizing producing sulphuric 

 acid. The greater part of the organic carbon, which it has been 

 pointed out is of enormous amount, must apparently be thus 

 oxidized, producing an equivalent amount of carbonic and sul- 

 phuric acids. The effects of this reaction are likely to be more 

 marked in the deeper parts of the ocean, where the motion of the 

 sea- water must be extremely slow, and where consequently the 

 effete products accumulate ; in this way the larger amount of 

 lime and carbonic acid and the less amount of oxygen in solution 

 in such waters is to be accounted for. Not only so, but the 

 very existence of such a relatively large quantity of sulphate of lime 

 in sea-water goes far to prove that this reaction must continually 

 take place, seeing that sulphuric acid cannot exist in a free state 

 in the presence of carbonate of lime. Thus it is probable that 

 the quantity of sulphate of lime in solution in the ocean is only 

 limited by the amount of organic decomposition which takes place 

 in its waters. On the other hand, if marine organisms procure the 

 whole of their carbonate of lime from the sulphate of lime by the 

 reaction of ammoniacal salts, then the amount of lime that may 

 be secreted from ocean waters is likewise limited by the amount 

 of organic matter undergoing this oxidation process in the ocean. 

 Gmelin, in his "Chemistry," vol. ii. p. 191, refers to this 

 decomposition as follows : — 



NO. 1076, VOL. 42] 



" In hot climates, as on the west coast of Africa, where the 

 water of rivers charged with organic matter mixes with sea- 

 water, hydrosulphuric acid, sometimes to the extent of 6 cubic 

 inches to the gallon, is found in sea-water, even at a distance of 

 27 miles from the mouth of the rivers." 



This is also confirmed from samples of water which we have 

 received, taken from the roadstead of Monte Video by the 

 telegraph ship Seine. 



If now we turn our attention to the solution of dead carbonate 

 of lime in shells and coral skeletons by the action of sea-water, 

 it will be found that the rate of this solution varies greatly 

 according to the conditions in which these remains are exposed 

 to the solvent power of the water. A large number of experi- 

 ments have been conducted with the view of deterniining the 

 solubility of carbonate of lime under its different conditions. It 

 may be pointed out that the normal amount of carbonate of lime 

 dissolved in sea-water is very small, strikingly so (o* 1200 grammes 

 per litre) when compared with the vast amount of this substance 

 continually being secreted from the sea by organisms. Sea- water 

 can, however, take up 06490 grammes per litre of carbonate of 

 lime in an amorphous (or hydrated) condition, forming a clear 

 supersaturated solution, but after a time not only the excess so 

 added is thrown down, but also sometimes a portion of that nor- 

 mally present in the water itself. It would thus appear that it 

 is unable permanently to retain in solution more of this substance 

 than is usually found present in sea-water. This peculiarity of 

 sea-water, after taking up a large amount of amorphous car- 

 bonate of lime, and throwing it out in a crystalline form, accounts 

 for the filling up of the interstices of massive corals with crystal- 

 line carbonate in coral islands and other calcareous formations, 

 so that all trace may ultimately be lost of their original organic 

 structure. These experiments show a great diversity as to the 

 amount of carbonate of lime which will pass into solution in sea- 

 water from various calcareous structures in a given time. As a 

 rule, the more definitely crystalline the substance is, the less it is 

 soluble. Calcspar is less soluble than massive varieties of coral, 

 and these again less than the more porous varieties. We have 

 already indicated that amorphous or hydrated carbonate of lime 

 is (in that condition) much more soluble than any other form of 

 the substance. The rate of solution is also much greater when 

 the water is constantly renewed, than when the same water 

 remains in contact with carbonate of lime. The water quickly 

 becomes saturated and unable to exert further solvent action. 

 In this connection we found that different samples of sea-water 

 from different localities possessed very different solvent powers. 

 Especially was this the case between summer and winter waters, 

 the former having distinct solvent action on coral skeletons, 

 whilst with the latter there was hardly any. The lower specific 

 gravity of winter waters may be regarded as to some extent 

 reducing their solvent power, but this is more probably to be 

 attributed to the absence of free carbonic acid — that is, carbonic 

 acid in excess of what is required to saturate the free base in the 

 sea-water as normal carbonate. To test this point, carbonic 

 acid was added to one of these winter waters (which had no 

 solvent action on coral), the quantity added not being sufficient 

 to destroy its alkaline character. It was found that in these 

 circumstances an appreciable amount had been dissolved. 



This appears to indicate that there is more carbonic acid in 

 summer than in winter waters in our latitudes, due probably to- 

 the increased activity of animal life. Mr. Buchanan's observations 

 on board the Challenger show that the carbonic acid present in 

 sea-water, over and above that necessary to form normal carbonate 

 of lime, was subject to great variations. It appears that this is a 

 much more effective agent in theremoval of carbonate of lime shells,. 

 &c., than the solvent power of sea-water itself (although artificial 

 sea- water quite free from carbonic acid dissolves carbonate of lime). 

 Buchanan's observations have also shown that carbonic acid as a 

 rule is more abundant in bottom than in surface waters ; and 

 Reid's experiments show that carbonated sea-waters under high 

 pressure take up more carbonate of lime than that at a normal 

 atmospheric pressure. The fact that carbonic acid is more 

 abundant in deep waters is evidently connected with the respira- 

 tion, and also the decay, of the animals which live and die on 

 the ocean floor ; and also with the decay of those which fall 

 from the surface. The water filling the deeper hollows has also 

 in its passage to the equator passed over thousands of square 

 miles of this floor covered with living animals, and as this water 

 has a very slow motion, and is but slowly renewed, we would 

 expect an accumulation of carbonic acid and deficiency of oxygea 

 in these abysmal depths. When, therefore, carbonate of lime 



