1890-91.] Dr Murray and Mr Irvine on Silica in Seas. 
249 
the organic matter had become putrid, the water was carefully 
filtered from the sediment, and the silicic acid determined in the 
nitrate. The amount found was equal to 0*025 grm. per litre, or, 
according to the amount of water, 1 part of silica had been dissolved 
from the Diatom Ooze in 41,000 parts of sea-water. This action of 
silicic acid in decomposing carbonate of lime was further proved by 
exposing 2 grms. of the two oozes to boiling water for half an hour, 
the amount of silicic acid present in a soluble condition after that 
period amounting to 0*014, or 1 in 80,000 of water. To check this 
result, and at the same time to determine whether the decomposing 
action of silicic acid upon carbonate of lime was continuous, a 
portion of the mixed oozes was heated with successive quantities of 
sea-water, when it was found that this action was constant. Thus, 
in a mixture of 89*42 per cent, of calcareous organisms and 10*58 
per cent, of siliceous organisms, the amount of silica was reduced, 
by 25 successive litres of sea-water, from 10*58 to 3*47 per cent., so 
that 67 per cent, of the silica present was removed.* 
On looking at the Tables showing the amount of suspended clay 
in sea- water (see pp. 241 and 242), and comparing the amount with 
the soluble silica or silicates in sea- water, it is to be observed that 
the maximum amount of silica found is much larger than that 
present as suspended clay. In the actual determinations of this 
body in the seven waters (shown in Table III., p. 243), the 
amount of clay found in these waters ranges from 264 to 8000 
tons per cubic mile of water, thus roughly representing from 132 to 
4000 tons of silica per cubic mile; whilst soluble silica, by the 
analysts’ results we have quoted, appears at a much higher figure. 
* In this connection Julien states (“On the Geological Action of Humus 
Acids,” Pros. Amer. Ass., vol. xxviii. p. 359) — “Considerable evidence now 
exists that a substance corresponding to humus, simply in its yield of acid 
solvents of lime, oxides of iron, manganese, &c., enters universally into the 
constitution of the layer of ooze upon the bottom of the ocean. Its exact com- 
position has never yet been determined ; but it may be suspected that it 
resembles that of glairine, especially in its high content of silica. As it has 
resulted from the continuous decomposition of the cellulose membranes of the 
diatomacese, &c., and of the gelatinous sarcode of the radiolaria, spongise, and 
foraminifera, which may be there living or deposited by subsidence from the 
surface, its composition must differ widely from that of the humus of subaerial 
eremacausis, in its large proportion of water and nitrogen and in its poverty 
in carbon. It must thus present the most favourable conditions for rapid 
dissociation.” 
