2S 
NATURE NOTES 
first because this substance is less soluble than the rest. Next, 
crowding round the margin of what was the water, come 
numbers of tiny cubes, some of which we may make out as 
having their faces hollowed out in a series of step-like squares, 
such as are often seen on a larger scale in the salt-pans of 
Cheshire. These cubes are mainly the common salt or sodium- 
chloride, by far the most abundant of all the substances dis- 
solved in sea-water, appearing last in the evaporation because 
it is the most soluble. Common salt constitutes in fact more than 
three-quarters of the whole amount of salts present. The bitter- 
ness of the water is due to magnesium compounds, which rank 
next in abundance to the common salt, and are mostly in cubical 
crystals not readily distinguishable from those of that substance. 
The flatness or alkalinity is produced by calcium-carbonate, 
familiar to us on a large scale as Iceland-spar or as marble, but 
occurring in sea-water in remarkably small proportions. As 
each salt has its own definite crystalline form, could we accu- 
rately sort out the tiny crystals resulting from our experiment, 
we might judge of the proportion in which each is present. 
More precise methods teach us that, while a gallon of sea- 
water weighs about 70,000 grains, more than 67,600 of these are 
represented by pure water ; and, of the 2,393 grains of saline 
matter, 1,964 are common salt, 256 magnesium-chloride, 98 cal- 
cium-sulphate, 53 potassium-chloride, 16 magnesium-sulphate, 
rather more than 2 calcium-carbonate and 2 magnesium-bromide. 
As to the source of these salts which we find in sea-water, it 
is now generally believed that the ocean has been salt from its 
beginning. On what is known as the Nebular Hypothesis of 
the early history of our globe, all the waters existed at first as 
vapour in the hot primeval atmosphere, and, in being precipi- 
tated as heated rain, would carry down with them many more 
or less volatile saline substances in solution. But even if this 
were not the case, and the ocean was at first fresh, it would 
now be salt and is probably constantly becoming more so. 
Pure water is ever being drawn up from the sea as vapour into 
the atmosphere by the sun’s heat, the salts being left behind as 
they were on the slide of our microscope ; so that the ocean has 
been compared to a vast retort of which the sun is the furnace 
and in which the saline solution is being gradually concentrated. 
This evaporated water condenses in the upper air to fall as rain, 
soaks into the earth to feed the springs, and rises into the rivers, 
constantly in its passage through and over the rocks leaching out 
any soluble matter with which it comes in contact and carrying 
it down to the ocean, where these salts will accumulate while 
the water is again evaporated to repeat its task. 
Since every chemical element seems capable under some 
circumstances of being held in solution in water, traces of most 
elements have been detected in sea-water. Many of the plants 
and animals that inhabit the ocean require calcium-carbonate 
or silica to build up their skeletons. It has been suggested that 
