CHAPTER II.

THE FREEZING OF STILL WATER-EXPANSION

OF WATER BEFORE FREEZING BEAUTY AND WISDOM OF THE ARRANGEMENT-THE FREEZING OF RUNNING WATER-GROUND-ICE-EXAMPLES OF ITS FORMATION IN DIFFERENT COUNTRIES-AMAZING FORCE OF WATER IN FREEZING-ECONOMICAL USES OF ICE-ICE-MAKING IN INDIAAMERICAN TRADE IN ICE-THE WENHAM LAKE ICE COMPANYSKETCH OF THEIR PROCEEDINGS IN CUTTING, STORING, AND EXPORTING ICE-ICE-HOUSES-PORTABLE ICE-HOUSE-GREAT USE OF ICE-HOUSES-CUTTING AND STORING OF ICE IN RUSSIA-ICE-CELLARS

-FROZEN MARKETS

To understand the manner in which water becomes ice, it is necessary to remember that the general effect of heat is to expand bodies, while that of cold is to contract them. Cold water occupies less space in a vessel than hot; for the heat, by separating the particles of the water, increases its bulk; hence, also, warm water is lighter than cold, and floats upon its surface.

Any one, on first becoming acquainted with the condensing power of cold, would naturally suppose

that the bulk of water would go on constantly diminishing by increased cold, until it became ice; but if such were the case, the ice of our lakes and rivers would not remain upon the surface, but would sink to the bottom, and every successive layer would also sink in the course of freezing, until the whole became frozen.

There is, however, a very remarkable and beautiful exception, in the case of water, to the general law above stated. As soon as the temperature of the water sinks a little below 40°, it ceases to contract by cold; and any further reduction of its temperature produces quite a contrary effect, causing it to expand, and consequently to become lighter, until it reaches the freezing point, namely, 32. At this point, a further and sudden expansion takes place, and it becomes ice. If it were not for this beautiful provision, our ponds and lakes would at almost every frost become solid masses of ice, which the heat of the next summer would scarcely suffice to melt: the fish, and other tenants of the pool, would be destroyed; the temperature of our climate would be materially altered, and the consequences would be very serious..

To make this subject more clear, let us suppose

a freezing wind to be blowing over a lake. This will soon cool the water at the surface, and make it sink; and will continue to do so until the water at the surface has reached the temperature of about 391, its point of greatest condensation. After this, the continuance of the cold will indeed lower its temperature; but instead of making it contract as before, it actually causes it to expand, and by making it lighter, keeps it at the surface, and thus prevents the waters beneath from cooling down. The surface water continues to cool and to expand, until it reaches the temperature of 32o, when a sheet of ice is formed. This serves as a further protection to the water below from the cold wind. A long continuance of cold will thicken the surface ice, but be slow in penetrating to any considerable depth.

Such is the manner in which water freezes in lakes, ponds, and placid rivers. But in rapid and rugged streams, the case is often different. The eddies and irregularities of the stream, as it flows. over a rocky channel, have the effect of mixing the layers of water together; so that the cooler surface, at one moment exposed to the freezing air, is at the next moment hurried to the bottom of

the stream. All parts of the water are therefore of about equal coldness. Such rivers do not often freeze on the surface, where the motion of the water is the strongest; but a spongy sort of ice frequently forms on stones and other projections at the sides and bottom of the stream, and sometimes extends over the whole bed of the river. This is the substance called by the Germans, grundeis, or groundice, respecting which there has been much difference of opinion among scientific men. Some persons continue to doubt whether ice can possibly be formed in this way; but the following instances are sufficient to prove it. The fishermen of the Elbe, when questioned on this subject, complained that during the cold days of autumn, long before any ice appeared on the surface of the river, the nets which were at the bottom of the stream often became encrusted with ice; also that the baskets used for catching eels, were often found covered with ice; that anchors which had been lost during the summer, floated on the surface during the winter, the ice acting like a cork to raise them up. This ice also raised the large stones to which the buoys were attached by chains, and occasioned much inconvenience by displacing these useful signals.

A few striking examples of the action of groundice are recorded by the Commander Steenk, of Pillau. In February, 1806, during a strong southeast wind, and a temperature a little above 34° Fahr., a long iron chain, to which the buoys of the fair-way are fastened, and which had been lost sight of in a depth of from fifteen to eighteen feet, suddenly made its appearance at the surface of the water, and swam there; it was completely encrusted with ice to the thickness of several feet. Stones also, of from three to six pounds weight, rose to the surface, surrounded with a thick coat of ice. A cable also, three and a half inches thick, and about thirty fathoms long, which had been lost during the preceding summer, in a depth of thirty feet, floated to the surface, enveloped in ice to the thickness of two feet. An anchor which had rested only an hour at the bottom, became so encrusted with ice, that it required not more than half the usual power to haul it up.

On the river Aar, a scientific observer noticed a quantity of floating ice appearing on the surface at a time when there was no sign of freezing either along the banks, or in shady places where the water was calm. It could not therefore be