Page:Popular Science Monthly Volume 92.djvu/476

 460 Popular Science Monthly

A Book Shelf and Trough Made of A Good Elastic Varnish for Coating

��Soft Wood

THE illustration shows the construction of a simple book shelf and trough com- bined. The sides are made of 1-in. yellow pine boards that taper in width from 14 in. at the bottom to 11 in. at the top. The strip at the top extends over the edges of the upright boards 1 in., and the base strip extends out 2 in. The shelves are fitted into grooves K i^^- deep. In the place of one shelf, a trough is set in which holds the books in an up- right position. The shelves are convenient for large volumes. Besides gluing all parts together,

���Dimensions of the parts that enter into the construc- tion of a simple combination book shelf and trough

��round head screws are used to strengthen the joints, and to im- prove the appearance. The completed book shelf can be finished with two coats of stain and one of either varnish or wax. For small jobs like this, it is best to procure finishing material in small cans from your dealer. Follow directions on the containers as differ- ent makers recommend different use of such products. — H. Alden.

Glass Cements for Commercial or Domestic Use

WHEN finely pulverized chalk is stirred into a solution of water glass at 30°B. until the resultant mixture becomes fine and plastic, a cement of extraordinary durability is obtained. It will harden in about seven hours. The cement, when mixed with a little zinc dust, will adhere to almost any surface. After burnishing, such a ce- ment will exhibit the white and brilliant appearance of metallic zinc. A small quan- tity of carbonate of copper added to the chalk will produce a bright green cement. Cobalt blue wil give it a .splendid blue coloration, vermilion a bright red, and car- bon red will produce a violet color.

��Blue Prints

THE greatest drawback to the use of drawings or blue prints in machine shops and factories, is that they soil so quickly owing to handling. This obscures

the dimensions of the various ma- chine sizes, mak- ing their reading slower, and al- lowing possibili- ties for mistakes. In order to keep blue prints clean and make them last longer, one chief draftsman coats them with a flexible and wa- terproof varnish. This enables the drawings, or blue prints, to be wiped off with a wet cloth when they become soiled. It taken into damp

��also allows them to be places.

The formula for the varnish is as follows: Crush transparent and clear pieces of gum damar into small grains, then place a con- venient quantity — say forty grains— in a flask. Pour on it about 6 oz. of acetone and expose the whole to a moderate temperature for about two weeks, or until the mixture has dissolved. It is necessary to shake the flask frequently.

At the end of this time, pour off the clear saturated solution of damar in acetone, and add to every four parts of the varnish, three parts of rather dense collodion, mixing the two solutions by shaking. The resulting fluid is allowed to settle and it can be pre- served in well closed phials.

This varnish is applied in vertical lines by means of a soft camel's hair brush. At the first application it will appear as if the sur- face of the paper were covered with a thin white skin. As soon, however, as the var- nish dries, it presents a clear shining surface. The varnish should be applied in three layers, or coats. It will be found by ex- perience, that this varnish retains its gloss and remains pliable under all weather con- ditions.— W. S. Standiford.

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