TRANSACTIONS OF SECTION G. 627 
of a rapid is of yearly occurrence. ‘Nowhere ‘can one witness a more ‘wonderful 
sight of the delicate poising of the forces of Nature than in one of the Canadian 
rivers in winter. The steadiness of the temperature of the water throughout the 
ice season is a matter of great interest. It seldom varies more than a few 
itthousandths of a degree from the freezing-point even in ‘the severest weather. 
This is true for rivers flowing too swiftly for surface ice to form, as well as for 
the quieter streams protected by an ice covering. 
In general, three varieties of ice are distinguished and present characteristics 
brought about by their method of production, Surface or sheet ice forms over 
the surface of quiet lakes or rivers, and is helpful or not depending on the 
particular conditions, Spicular ice, or as itis called in Canada, frazil ice, is formed 
by surface agitation in the more turbulent rivers, and in waterfalls, and accumu- 
lates in great quantities in the quieter portions of the stream where it is carried 
by currents. It varies in size from thin plates to fine needle crystals depending 
on the degree of agitation of the water, and of all the forms of ice it gives the 
most trouble in hydraulic work, Amnchor- or ground-ice is the most interesting 
form, on account of the fact that it grows along the bed of a river which is not 
covered by a surface sheet. It is formed in two ways: by the cooling of the 
bottom by the radiation of heat during cold clear nights, and by the freezing of 
frazil-ice carried down by the currents of water when in a super-cooled state. 
A bright sun has a great influence on the ice, and as soon as its rays are sufficiently 
high to penetrate to the bottom, the ice is detached and rises to the surface. in 
so doing it frequently brings up stones or boulders of considerable size to which it 
is attached. 
A study of the temperature conditions in the water during the production of 
these forms of ice shows that the freezing is accompanied by a small temperature 
depression in the water, amounting to a few thousandths of a degree from the 
freezing-point.1 During severe cold weather the water is thus thrown into a 
slightly super-cooled state, during which time the ice crystals grow rapidly by 
continued freezing, and give rise to the agglomerating stage, when they possess 
adhesive properties and form lumps and spongy masses. In this condition the ice 
is dreaded by power users, for it quickly adheres to the rack-bars and to the 
machinery of the wheel-gates and turbines. In a short time it interferes with the 
operation of the wheels, and may at any moment cause a temporary cessation of 
operations. Fortunately, it is only a minute temperature depression which brings 
about these conditions, and methods of artificial heat applied about the affected 
spots relieve the situation in a short time. An intelligent use of artificial heat, 
especially at night time when supercooling is most common, is found valuable im 
preventing any interference with the normal operation of a power-house. It is 
not necessary to warm the entire volume of water passing through, which would 
be very costly and difficult, but by applying the heat in the racks or wheel cases, 
or blowing steam about the affected parts, the ice is prevented from obtaining a 
foothold. The ice is as effective as so much water in producing a head, hence the 
necessity of passing it through, and never allowing it to freeze to the metal surfaces 
of the machinery, It is safe to say that where it is possible to apply even a small 
quantity of heat directly to the machinery and racks, a condition of affairs may be 
done away with which for many years has been regarded as involving inevitable 
interruption to the continuous operation of a plant. 
There are other causes at work, however, to interfere with the operation of 
power plants which depend on the particular spot where a power-house is 
located. Rivers like the St. Lawrence at Montreal are subjected to winter floods, 
occasioned by the accumulation of frazil- and disintegrated anchor-ice. Wherever 
open water or a rapid occurs above a surface sheet of ice, large quantities of frazil- 
ice are carried under by the currents, and settle upwards in the quieter parts. 
Large hanging dams of spongy ice are thus produced, which so reduce the avail- 
able waterway as to cause serious changes in level. Sometimes the channels 
become blocked entirely, and then the water backs up sufficiently to clear the ice 
1 Cases are known, however, where anchor-ice was formed by copious nocturnal 
radiation when the water was slightly above the freezing temperature. 
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