1890-91.] Dr Murray and Mr Irvine on Silica in Seas. 243 
in suspension by the sea- water depending largely on the temperature, 
and to a less extent on the salinity, being greater the lower the 
temperature and salinity. 
To ascertain the amount of clayey matter in suspension in the open 
sea far from land, we procured large samples from the surface of the 
Atlantic, the Indian Ocean, Red Sea, the Mediterranean, the German 
Ocean, the Baltic Sea, and the Firth of Forth.* These waters were 
preserved in stoneware jars thoroughly cleaned and filled with the 
utmost care, so that no siliceous matter might be accidentally intro- 
duced. About 14 litres of sea -water were passed through a double 
ashless filter, and, after carefully washing the solid matter left on 
the filter to get rid of salts, the whole was burned, and the residue 
treated in a platinum vessel with pure boiling sulphuric acid, — the 
silicic acid, iron, and alumina were treated in the usual way. The 
results are exhibited in the following Table — 
Table III. — Showing Amount of Mechanically- Suspended Silicates 
{Clay) present in Water of Different Seas. 
In 14 Litres 
of Water. 
Per Cubic 
Mile of Water. 
I. Firth of Forth, 1 mile from shore, 
II. Atlantic Ocean, lat. 51° 20', long. 
31° W., 
III. German Ocean, 30 miles E. of May Island, 
IY. Mediterranean, centre of eastern basin, . 
Y. Baltic Sea, salinity 1005 ‘5 
YI. Red Sea, off Brothers Island, 
YII. Indian Ocean, lat. 15° 46' N., long. 58° \ 
51' E., / 
0-0259 grm. 
0-0052 ,, 
0-0063 ,, 
0-0065 ,, 
0-0105 ,, 
0-0006 ,, 
0-0006 „ 
8000 tons. 
1604 „ 
1946 ,, 
2031 ,, 
3200 ,, 
264 ,, 
264 ,, 
In the first determination (I.), Firth of Forth, the amount of 
silica in the clay, represented above, is about one-fourth what our 
minimum results show as present in a soluble condition in sea-water. 
In Baltic water (V.), salinity 1005, about one-eighth; in Atlantic, 
German Ocean, and Mediterranean waters (II., III. and IV.), about 
one-sixteenth, and in the Indian Ocean and Red Sea still less. 
This seems to establish the fact that there is always a small 
* We are indebted to Captains Thomas S. Knox and George Read, of the 
Anchor Line, for collecting the waters from the Mediterranean, Indian, and 
Atlantic Oceans. 
