This compound is impervious to water, so the negative print is removed by simply washing with a damp sponge, the same as removing writing from a slate.  This makes it possible to place another original on the pad immediately without waiting for the ink to vanish by chemical action as in the original hectograph.

The action of the weather has no effect upon this compound and it is proof against accident, for the tray may be dropped and the pad dented or cut into pieces, and the clay can be pressed back and leveled.  The only caution is to keep it covered with a cloth saturated in glycerine while not in use.  —­Contributed by A. A. Houghton, Northville, Mich.

** Paper-Clip Bookmark [241]

The combination of a paper clip and a calling card makes a good bookmark.

[Illustration:  Bookmark]

The clip and card can be kept together by piercing the card and bending the ends of the wire to stick through the holes.  The clip is attached to a page as shown in the sketch.  —­Contributed by Thos.  DeLoof, Grand Rapids, Mich.

** Aerating Water in a Small Tank [241]

A simple way of producing air pressure sufficient to aerate water is by the use of a siphon as shown in Fig. 1.  The siphon is made of glass tubes, the longer pieces being bent on one end as shown.  The air receiver and regulating device are attached to the top end of the lower tube, as shown in Fig. 2.  The receiver or air inlet is the most important part.  It is made of a glass tube, 3/4 in. in diameter and 5 in. long.  A hole is filed or blown through one side of the glass for the admission of air.  The ends of the smaller glass

[Illustration:  Fig.1 Fig.2 Forcing Air Through Water]

tubes are passed through corks having a diameter to fit the ends of this larger tube.  The ends of these tubes should be so adjusted that the continuous drops of water from the upper will fall into the tube below.  The succession of air bubbles thus imprisoned are driven down the tube and into the tank below.

The regulator is placed in the tube or siphon above the air receiver.  Its purpose is to retard the flow of water from the siphon above and make it drop rapidly.  It consists of a rubber connecting tube with two flat pieces of wood clamped over the center and adjusted with screws.  The apparatus is started by clamping the rubber tube tightly and then exhausting the air in the siphon tube, then placing the end in the upper reservoir and releasing the clamp until the water begins to drop.  If the reservoir is kept filled from the tank, the device will work for an indefinite time.  —­Contributed by John T. Dunlop, Shettleston, Scotland.

** Imitation Arms and Armor-Part Ii [242]

Imitation swords, stilettos and battle-axes, put up as ornaments, will look well if they are arranged on a shield which is hung high up on a wall of a room or hall, says the English