164 



NA TURE 



[June 12, 1890 



the carbonate of lime is mostly derived from the shells of pelagic 

 organisms that have fallen from the surface waters, and it will be 

 noticed that these wholly disappear from the greater depths. 

 These figure", are derived from a study of the Challenger de- 

 posits alone, but they are confirmed, as to the general result, 

 by an examination of the deposits collected by the U.S.SS. 

 Tuscarora and Blake, by H.M.SS. Egeria and Investigator, the 

 ships of the Telegraph Construction and Silvertown Companies, 

 and other ships. One other peculiarity as to the distribution of 

 carbonate of lime organism? on the ocean's floor may be noted. 

 Where these calcareous shells are most abundant on the surface, 

 as in the tropics, the remains of the dead shells are as a rule 

 found at greater depths on the bottom than in temperate or 

 polar regions, where they are relatively much less abundant in 

 the surface waters. 



In his paper on the origin of coral reefs, published many 

 years ago, Mr. Murray pointed out that sea-water, rushing in and 

 out of the lagoon twice in the twenty-four hours, would take up 

 and carry away large quantities of the carbonate of lime which, 

 in the form of coral sand and mud, covers the bottom of these 

 shallow basins. Just as the surface shells are dissolved by falling 

 through the layers of ocean water, so in this case the dead coral 

 fragments are dissolved by the sea-water that continually passes 

 over them ; in this way, chiefly, he accounted for the formation i 

 of lagoons in atolls and barrier reefs. 



During the past few years a large number of experiments 

 have been carried on at the Scottish Marine Station for Scientific 

 Research, with the view of throwing some additional light on 

 the oceanic phenomena referred to in the preceding paragraphs, 

 in so far as these relate to the secretion and solution of carbonate 

 of lime under varying conditions. Those dealing with the 

 secretion of carbonate of lime by organisms will be considered 

 in the first place, and afterwards those treating of the solution 

 of the dead carbonate of lime shells and skeletons will be 

 discussed. 



A brief account of .'^ome of the experiments will show the 

 nature of the investigations, and indicate the results which have 

 been obtained in so far as they bear on the subject with which 

 we are dealing. 



Experiment i. A number of laying hens were shut up in awooden 

 building, all ordinary sources of lime being withheld. In a few 

 days the eggs, in place of a calcareous shell, had only a mem- 

 branous covering. Thereafter sulphate, phosphate, nitrate, and 

 silicate of lime were successively added to their otherwise lime- 

 less food, and from all these salts they were enabled to form 

 normal shells for their eggs consisting of carbonate of lime. 



From the investigations of Irvine and Woodhead it is believed 

 that the lime salts in passing through the blood assume the form 

 of phosphate, which is carried to the point of secretion, where it 

 is decomposed and deposited as carbonate. When magnesium 

 and strontium salts were added to the hens' food the eggs became 

 membranous and shelless. 



Ex. 2. Artificial seawater was prepared, from which car- 

 bonate of lime was rigidly excluded. In this water crabs after 

 ecdysis produced the usual exo-skeleton of carbonate of lime 

 from the lime salts, other than carbonate, present in the water. 



Ex. 3. The artificial sea-water of Ex. 2, which was perfectly 

 neutral before the introduction of living crabs, in the course of a 

 short time became distinctly alkaline in character. This was 

 found to be due to the decomposition of their effete nitrogenous 

 products, and the formation of carbonate of ammonia, and 

 ultimately of carbonate of lime. 



Ex. 4 and 5. Sea-water was mixed with urine and kept at a 

 temperature ranging from 60° to 80° F. After a time the whole 

 of the lime present in the sea-water was thrown down as 

 carbonate and phosphate. 



Ex. 6. A number of small crabs were placed in two litres of 

 ordinary sea-water, and were fed with mussel flesh. This water 

 was not renewed, the effete matters from the crabs passing into 

 it. After a few days the crabs died ; the water being then in a 

 putrid condition was set aside at a temperature of f o n 70° to 

 80° F., when it was found that practically the whole calcium in 

 the sea-water had been thrown down as carbonate of lime. 



Ex 7. We obtained absolutely fresh "liquor" from a number 

 of living oysters, and examined it before decomposition had 

 begun. It appeared to be a mixture of lymph with unchanged 

 sea-water. The specific gravity was i'023, in licatinj a con- 

 siderable admixture of fresh or river water. This liquor con- 

 tained 0*1889 grammes per litre of total lime in excess of that 

 present in sea-water of the same specific gravity, and its 



alkalinity was equal to 0-2581 grammes per litre in excess of 

 sea-water of the same specific gravity. 



Thus we had in this liquid an accumulation of total lime (in 

 excess of that present in sea-water) amounting too'iSSg grammes 

 per litre, the greater part of which was in the form of carbonate 

 in solution, presumably in an amorphous or hydrated condition. 

 Apparently this is due to the direct secretion of carbonate of 

 ammonia by the cells of the living animals, which, reacting on 

 the sulphate of lime in the sea-water, is capable of throwing out 

 nine-tenths of the soluble calcium salts present, in the insoluble 

 condition of carbonate. The oyster liquor was found to contain 

 saline ammoniacal salts in enormous excess over that which is 

 present in ordinary sea-water. 



Ex. 8. A similar experiment was made with the liquor taken 

 from living mussels. The results coincided with those obtained 

 in Ex. 7. 



Theoretically urea plus two molecules of water will give 

 carbonate of ammonia. If, therefore, this substance be a 

 stage in the formation of urea, it is not unnatural to suppose 

 that in shell-forming animals the shell-formation may take place 

 at this stage without the formation of urea at all. In these 

 experiments the usual method for the estimation of saline and 

 albuminoid ammonia could not be follo-ved, and we made use 

 of the following simple adaptation by which we obtained con- 

 cordant results. 



Absolutely pure potash was added to a measured and care- 

 fully filtered portion of the sea-water under examination, and 

 the precipitate formed removed by filtration. The clear filtrate 

 was then Nesslerized in the usual manner. We had thus an 

 accurate means of determining between the actual ammoniacal 

 salts and the albuminoid matter, both of which are, as a rule, 

 present in sea-water according to the amount it carries of living 

 and dead organisms. To satisfy ourselves that the addition of 

 pure potash to a fluid containing albuminoids alone does not 

 give rise (immediately) to the production of saline ammonia, we 

 treated pure albumen taken from a newly laid egg in this 

 manner, as also urea, without obtaining any trace of ammoniacal 

 reaction. 



These experiments show the alteration in the constitution of 

 the lime salts in sea-water, both by the decomposition of effete 

 matters thrown into the sea by animals, as also by the secretion 

 of carbonate of ammonia by the cell action of the animals. 



Sea-water collected among the coral atolls of the Louisiade 

 Archipelago, received from Captain Wharton, F.R. S., Hydro- 

 grapher to the Admiralty, contained per million parts — 



0-48 



o-i8 



Saline ammonia ... 

 Albuminoid ammonia 



066 



NO. 1076, VOL. 42] 



whilst water collected by the Challenger in the North Atlantic 



(lat. 30° 20' N. long. 36° 6' W.) contained — 



Saline ammonia o'26 



Albuminoid ammonia ... ... ... ... o'i6 



042 

 and water from the German Ocean near land contained — 

 Saline ammonia ... ... ... ... ... o'r3 



Albuminoid ammonia ... ... ... ... o'i3 



0-26 



This is exactly what we were led to expect from the experi- 

 ments enumerated — the greatest amount of saline ammonia 

 being present where the greatest animal life activity existed, as 

 in the waters from the coral sea ; and least in the German 

 Ocean winter water where it was at its minimum. 



Thus the whole of the lime salts in sea- water may, under these 

 circumstances, be changed into carbonate, and in this way may 

 be presented to the coral and shell builders in the form suitable 

 for their requirements. 



The temperature of the water is of great importance in this 

 reaction. In cold water, of which the great bulk of the ocean 

 consists, the decomposition of nitrogenous organic matter is 

 retarded, whereas in tropical surface waters it proceeds with 

 great rapidity. Thus coral reef builders and pelagic organisms 

 may not only benefit by the decomposition arising from their 

 own effete matter, but also from the undecomposed nitrogenous 

 matter carried to equatorial regions from the cold water of the 

 deep sea, or from polar regions. 



