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ted salts, if given in large quantities, are poisonous, one 400th part 
of its own weight of marine salt will kill any animal. Sea water 
owes its bitter taste to the sulphate of magnesia it contains, better 
known to most of you as Epsom Salts. Pliny tells us the ancient 
Romans used to transport waters of the Dead Sea at enormous 
cost into Italy, where its curative properties were highly prized. As 
we know, the waters of the Dead Sea contain relatively more saline 
matter, than any other sea, no less indeed, than six times as much. 
We all know how much easier it is to swim in sea water than in fresh, 
but so great is the density of the water of the Dead Sea that it is 
difficult to sink in it, and the body of a man floats on its surface. 
This great density is due to the fact that no considerable rivers flow 
into the Dead Sea, so that the loss by evaporation goes on more 
rapidly than the supply of fresh water. This is the reason why 
tropical oceans are more salt than northern seas. At the tropics 
evaporation goes on so rapidly that three-quarters of an inch of the 
surface water is taken up in twenty-four hours, which amounts to 
a layer of no less than 22 feet each year, while in the north, 
evaporation is far less rapid, and the sea receives enormous 
volumes of ice, which is practically fresh water. Sea water ice, 
when dissolved, contains no saline matter, or rather it contains 
only a very small proportion which is mechanically entangled 
amongst its particles. Sea water, when pure, is quite inodorous ; 
when it has any smell, it is because it contains animal or vegetable 
matter in solution or suspension, as often happens on our coasts or 
in harbours. Oysters and other shell fish, especially mussels, will 
live and thrive in sea water loaded with animal matter in a state of 
decomposition ; part of this they absorb and transform in their 
interiors into certain very poisonous alkaloids, which chemists call 
Ptomaines. This is the explanation of the poisonous effects 
occasionally produced by eating muscles and other shell fish. Al- 
though sea water is, owing to the salts of magnesia it contains, 
usually very unpleasant to the taste, yet oyster eaters will recall 
the agreeable taste of the water found in the shell of the oyster, 
and which the animal has stored up in order to carry on respiration. 
This is due to the fact that this pent up fluid contains always more 
or less of the vital juices of the animal itself, which was wounded 
by the knife in the act of opening the shell. 
The problem how to render sea water drinkable, has engaged 
. the attention of mankind for at least 1800 years, and even now, 
despite all our science and chemical improvements, remains prac- 
tically unsolved. Pliny asserted that a bottle hermetically sealed 
and sunk deep into the sea, would return to the surface filled with 
pure water. This statement was implicitly believed until modern 
times, when a sceptical Italian (Cosigny) tried the experiment, 
e 
