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April, 1917 for metal. Owing to the unequal ex- pansion and contraction of the metal of the boiler and the scale in it, the latter, during alternate periods of heating and cooling becomes more or less cracked and checked. When the fire is applied to the cold boiler the metal will expand rapidly, the scale does not, and therefore cracks, checks and fissures open in the scale from the surface to the metal. How the Graphite Works The presence of these little cracks gives an opportunity for the proper graphite to disintegrate and break down old scale regardless of its character and thickness. Circulating with the water the graphite works into and through these openings (which otherwise are almost immediately recemented by the scale-forming matter in the water) and deposits on the inner surfaces of tubes and shell between the metal and the scale. The result is that the latter will no longer adhere tenaciously and may be removed with comparative ease. These cracks cannot be recemented because they are coated with graphite from the surface of the. scale to the metal. Owing to the convulsions that occur continuously ‘in a boiler when under steam, a piece or slab of scale momen- tarily is released from the metal. the slab and metal and it cannot be re- cemented. If the scale is thick, it some- times comes off in large strips or slabs; if thin, it sloughs off in the form of sludge or small scales. After a boiler has been once cleaned of its accumula- tion of old scale the continuous use of correct quantities of graphite will effec- tively prevent the subsequent formation of the hard scale because it will, as stated previously, form in and with the scale matter and keep the latter in such a loose, soft condition that it may be taken out easily. With some waters the. graphite may entirely prevent the formation of the scale that may not be eliminated by blowing down and washing out. Gener- ally speaking, however, most feed waters carry scale forming materials in such a quantity that a coating will form to some extent in spite of the presence of graphite; but the graphite will make the coating so soft that it may be removed with comparative ease, thus making boiler cleaning more ‘simple. The action of the graphite in keeping the scale soft is similar to its action when mixed with concrete. A _ small amount of cement can be mixed with water and allowed to set. It will be- come as hard as flint. On the other hand. take the same quantity of cement and water.mixed with a very small por- tion of this finely-powdered, amorphous graphite and the cement will not set hard: it can even be crumbled and broken quite easily with the hands. The . graphite immediately passes in between. boiler. “THE MARINE REVIEW While scale forms in some instances despite the use of graphite, the graphite mixing with the scale not only keeps it soft, but makes it a far better conductor of heat than would be the case if the graphite were not present. Scale im- pregnated with graphite is a better con- ductor of heat and exercises the same functions as graphite in crucibles, which are made of graphite because of its great heat conducting qualities. As a matter of fact, graphite, next to metal, is one of the best heat conductors known. The use of the graphite in preventing the formation of scale is simple. It is continuously introduced into a_ boiler with the feed water in the proportion Magnet to Find Ships? A sub-sea magnet invented by a Japanese scientist named Nakahara is designed to be instrumental in locatina many of the sunken sub- marines, warships and_ transports which have gone down in compara- tively ‘shallow water. Recent tests of the magnet over the Japanese naval target grounds are said to have disclosed thousands of project- iles fired in practice. At the pres- ent price of scrap iron, the 600,000 shells which lie scattered at the bottom of the Japanese bays are worth some $3,000,000. Jt is hoped to use the magnet in extracting the shell scraps from the soil of the European battlefields. of approximately three ounces to every 1,000 gallons of water evaporated, or about one pint (34 pound) to 100 horse- power for every-10 hours of operation. This graphite therefore is in continuous circulation in the boiler. Both graphite and the solids of the water which are being precipitated through the agency of the heat, have an affinity for each other. They may float for a while as light flocculent particles on the top of the water, gathering together and getting heavier all the time until finally they settle into a kind of sludge or mud that is easily disposed of through the blow off. Another great advantage in using the graphite, in addition to satisfactory dis- position. of scale difficulties, is that it does its work without harm to the Instead of exercising a pitting or corrosive influence on the metal it tends to coat and protect the metal from the corrosive influences of any free acids that may be’ in the water. The Dominion government has award- ed contracts for two auxiliary schoon- ers, one to the Wallace ship yards, North Vancouver, B. C., and the other to the Cameron Genoa Co., Victoria, B. C. Each of the schooners wi!l cost about $250,000. 147 Book Review Strength of Ships, .by Athole J.. Murray; cloth, 400 pages, 6x9 inches; published by Longmans, Green & Co. and furnished by The Marine Review for $5 net. The increasing complexity of ship: construction is producing a growing demand for a fuller and more wide- spread knowledge of the strength problems underlying ship design. Up: to the present, few, if any, books: have been published in the English language devoted to this subject ex— clusively. Strength of Ships is de- signed to meet this need. The subject has been treated from: a practical standpoint, although some: intricate calculations have been in- troduced, especially where the re- searches are new, as for instance, when dealing with the subjects of bulkheads, curved bars and_ stanch- ions. Ship builders will find the sec— tion on bulkheads of interest in that a. logical method for co-ordinating bulkhead test data is presented. The elements of the theories of stress, strain and elasticity are con- cisely set forth, and later their appli- cation is shown to problems of de- sign involving beams, columns, shafts, bulkheads, plating, riveting, brackets, rudders and miscellaneous fittings.. Considerable space is devoted to longi-- tudinal and transverse strength. New Hudson Bay Dock A dock, capable of accommodating ocean-going vessels, has just been com-- pleted at Port Nelson, on Hudson bay, according to an announcement by Cap-: tain Freakly, government navigation agent at the new northern port. The dock, built at the mouth of the Nelson river, 3,000 feet from shore, is con- nected with the mainland by a steel trestle over which trains will run to reach the ships. Captain Freakly said that grain ele- vators and warehouses will be located on the new dock, which was built far out in the river, because of extensive tide flats between navigable water and the mainland. Lewis M. Stoddard, lighthouse in- spector at Milwaukee, Wis., has issued notice that when Milwaukee light vessel No. 95 is returned to her station, the intensity of her light will be changed from 500 candlepower to 1,000 candle- power, and the characteristic will be changed from: occulting white, 15 sec- onds, light, 12 seconds, eclipse,3 seconds to group occulting white, 15 seconds, light, 1 second, eclipse, 1 second, light, I second, eclipse, 1 second, light, 1 second, eclipse, 1 second, light, 8 seconds, eclipse, 1 second.