In assembling the parts care must be taken not to wrench the shaft or other pieces out of line, and in general, it is well to fix nonadjustable parts solidly when they are fitted into place. This applies particularly to the engine bed and the shaft log. The bearing block may be adjusted vertically by adding packing, or by reducing the lower surface. The rudder and its fittings may be made in regular course, but should not be fitted until the power unit and driving mechanism is in place finally. The propeller may be protected from possible injury by laying it aside until needed. All the openings in the hull through which bolts or other fastenings are placed should be packed with red lead or other waterproof packing. The working parts and finished metal surfaces should be oiled or greased thoroughly as the parts are assembled, and the unfinished metal parts painted with red lead. This will protect them from moisture and aid in the smooth operation of the mechanism.
How to Make a Fluorescent Screen
Many experimenters have occasion to use a fluorescent screen, particularly those interested in X-ray work. Such a device is quite expensive if purchased, and may be made as follows:
Mix 1 oz. each of common salt, sodium tungstate, and calcium chloride. Place the mixture in a crucible and heat it dull red in a coal fire, for several hours. It will melt into a clear liquid, and should then be removed and permitted to cool. The liquid will crystallize into a hard glasslike mass. Break this out of the crucible and crush it into small pieces. Put them into a jar of clear water. The sodium chloride resulting from the chemical change by heating, will gradually dissolve and the calcium tungstate will fall to the bottom in fine crystals. Wash this precipitate until all trace of the salt disappears; then pour the crystals upon a sheet of filter or blotting paper to dry. After drying, place them in a mortar and grind them to a fine powder, when they will be ready for use.
To make the screen proper, procure a piece of thin white cardboard of the size desired. The calendered board known as three-ply is satisfactory. Paint the cardboard on one side with a thick solution of gum arabic in water, or better still, with celluloid dissolved in amyl acetate. Permit the gum to become “tacky” before dusting with the chemical. The latter process requires care, to produce an even layer on the cardboard, and it is advisable to practice with ordinary salt before attempting it on the cardboard for the screen. The calcium tungstate should be placed in a dry jar, and a piece of fine muslin fixed over the mouth of it. The chemical may be dusted over the surface with this sieve jar.
Shake off the superfluous crystals and permit the screen to dry thoroughly. Fasten a piece of mica, or sheet celluloid, over the sensitized surface to prevent damage to it. Mount the sensitized cardboard in a wooden frame of suitable size and arrange a hood around its edges to cut out unnecessary light. The sensitive side of the screen is, of course, held toward the observer when the apparatus is used.—Contributed by Chester Keene, Hoboken, N. J.
Preventing Wire Mesh from Rising between Fence Posts
Fences which inclose pastures for hogs, or other smaller animals, are usually stretched to give rigidity and strength. Often the adjustment of the wire, after being put into place, causes it to rise from the ground between the fence posts, permitting the animals to escape. An effective method of holding the wire close to the ground is shown in the sketch. A peg, notched near its upper end, is driven into the ground so that the lower edge of the wire mesh is held fast in the notch.—Contributed by O. B. Laurent, New Roads, La.
The Notched Stake Holds the Wire Mesh Down between the Posts Where It Has a Tendency to Rise from the Ground