Popular Science Monthly
��909
��Skating on Salt
The idea of using crystalline salts, such as the carbonates and sulphates of sodium, potas- sium and other substances having like properties, has also been suggested. The salts are boiled and then poured direct- ly on a water-tight floor, hav- ing raised edges. The floor should be laid in sections, by means of a frame for holding the melted salts. After they solidify, the frame can be used for an adjacent section.
This same method has been improved so that a good per- manent sliding-surface is ob- tained. When the rink be- comes badly scratched, due to excessive use, heat is applied by means of a. rectangular frame supporting a wire lattice- work. The frame is placed on the floor and a rubber bag, filled with steam, is laid on the lattice- work. The action of the heat melts the salts, so that a flat, smooth surface is formed.
Another device for heating resembles an ordinary garden rake. Steam is blown on the floor through a longitudinal slit in a tube. The tube has a handle and two runners for guiding it across the floor. The pipe for supplying the steam passes down the handle and
����Intersecting channels underneath the salts are filled with water to be taken up by the porous layer
��POROUS SUBSTANCE MAGNESIUM CHLORIP.
CRYSTALLINE SALTS^
The porous substance permits the surplus moisture to pass from the magnesium chlorid to the crystalline top layer or vice versa
��connects with the lower horizontal tube. This smoothing process is too frequent- ly necessary, owing to the varying degrees of humidity in the atmosphere. To do away with this difficulty, at least partially, one inventor places a thick sheet of sodium carbonate upon a layer of porous material, which, in turn, rests upon a floor having many inter- secting channels. Water, circulated through these channels, is absorbed by the porous material and thus comes into contact with the top layer. This tends to pre- vent the air from affecting the sodium carbonate, but does not completely overcome the difficulty.
The nearest approach to perfection is a combination of substances now l^eing used in Germany with success. Be- low the porous layer is a sheet of some hygroscopic (water- attracting) substance such as magnesium chlorid. When the air is humid, the excessive moisture from the crystalline top layer passes into the mid- dle porous layer, and then into the bottom layer; when the air is dry, moisture reaches
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