JUNE 18. THE NEW ZEALAND GAZETTE. 2463

certain proportion of common air, has been known
to explode when a naked light has been brought in
contact with it: What is the composition of the gas?
Where is it found—in bunkers, ’tween decks, pockets,
and coal-shoots? How may it be got rid of as soon
as it evolves from the coal? How many cubic feet
of air to one of the gas forms a violent explosive
mixture?

195. A lighted lamp or candle has sometimes been
     lowered into an apparently empty paraffin-tank and
     produced an explosion resulting in injury to the
     person holding the light: what did the tank probably
     contain, and what produced the explosion?

196. In vessels carrying coal cargoes it has been
     observed that, generally speaking, the gas which
     escapes from the body of the coal is found more
     abundantly in the forward end of the hold than at
     the after end: why should this be so?

197. In recently opened ballast-tanks, double
     bottoms, and boilers a light lowered into either has
     sometimes been extinguished: what would, in all
     probability, cause this?

198. In double-bottom steamers where does the
     bilge-water lie, and where are the roses of the bilge-
     pipes fitted?

199. What is the advantage of a large rose over a
     small one?

200. Why, especially in vessels carrying cargoes
     liable to shift, should engine bilge-suctions be fitted
     to both wings of the bilge?

201. In a heavily listed vessel, why is it difficult
     to keep steam?

202. If the engine bilge-pumps get choked and
     water accumulates in the stokehold bilges, what effect
     does the water have upon the bilge-boards and stoke-
     hold-plates when the ship is rolling violently?

203. In a triple-expansion engine what spare gear
     do you consider necessary in the case of a foreign-
     going ship? Also, what stores would you provide
     for a voyage to England?

204. What means are sometimes provided for
     temporarily coupling together the broken parts of,
     say, a tunnel-shaft? Describe the fitting.

205. Does the pressure on the thrust collars vary
     with the horse-power, or with the speed of the ship,
     or how?

206. If the holding-down bolts of a thrust bearing
     should become slack, what effect would it have upon
     the working of the engines?

207. In an engine with three cranks which of the
     three is subject to the greatest torsional stress (1) in
     going ahead, (2) in going astern?

208. Is it usual to make the crank-shaft of a triple-
     or quadruple-expansion engine in one piece? And
     is the diameter of the shaft uniform from end to
     end? Give your reasons for the practice which
     obtains.

209. In a “built” crank-shaft how are the webs
     rigidly secured to the pins and to the body of shaft?

210. There are various descriptions of donkey-
     engines in use on board ship for pumping purposes;
     some pumps are fitted with escape-valves, some are
     not: why should this be?

211. Explain the functions of an air-vessel fitted
     to a feed-pump. Make rough hand sketches of
     (1) a satisfactory vessel, (2) an unsatisfactory vessel,
     where, say, the air-spring has been destroyed by care-
     lessness, or has never been properly provided.

212. Should cocks or escape-valves be fitted to air-
     vessels: why, or why not?

213. Where, by preference, should the escape-
     valve of a feed-pump be placed? Why?

214. Scum-cocks are sometimes fitted to boiler-
     shells at a height convenient for engineers to manipu-
     late when standing in the stokehold; the scum-pipes
     in such cases are led upward, inside the boiler, to a
     little above the combustion-chamber tops: what
     danger may arise from this arrangement?

215. Cocks for testing the water-level of boilers
     are sometimes fitted within reach of the engineer who
     is standing in the stokehold; these may have internal
     pipes leading upward and terminating at various
     levels: under what circumstances may these become
     misleading?

216. Why should the pipe which leads from the
     bottom of the water-gauge column to the bottom of
     the boiler-front, or back, be covered with non-con-
     ducting material? Why, also, should it never have
     lengthy horizontal bends?

217. In your own experience, how frequently is
     this pipe removed and cleared?

218. Why, even with the best of water-gauges,
     is it advisable to occasionally use the drain-cock?

219. Steam-loops have sometimes been inadver-
     tently made in the length of piping leading from the
     top of the water-gauge column to the top of the
     boiler: roughly sketch such a loop, and explain the
     danger arising from its existence.

220. Describe your method of thoroughly testing
     the water-gauge system to satisfy yourself that all
     the cocks and pipes are clear. [Your answer can be
     written on a supplementary sheet of foolscap, which
     the Examiner will hand you. Hand-sketches, mere
     lines indicating pipes and circles indicating cocks,
     should be made. Identify the cocks and pipes by
     letters or numerals.]

221. Describe the construction of a water-tube
     boiler, mentioning the type selected.

222. In a water-tube boiler, how is an economizer
     fitted, and what is its duty?

223. How is the water-gauge fitted in a water-
     tube boiler? Are glass gauges used?

224. The pressure of the steam in water-tube
     boilers is sometimes greater than at the engines: why
     is this, and what percentage above the engine-pres-
     sure does it amount to? How is this difference of
     pressure maintained?

225. Describe any automatic method of feeding
     water-tube boilers. Of what materials are the tubes
     made?

226. Describe the construction of any steam-tur-
     bine you are acquainted with which is used on board
     ship. How is the expansion of steam effected?
     How many propeller-shafts are employed, and how
     many propellers?

227. Is the same power in a steam-turbine avail-
     able to go astern as to go ahead?

228. Of what material are the propellers made in
     a steam turbine?

229. How many pounds of coal per indicated horse-
     power per hour are burnt with this type of engine?
     Name the type of boiler in use.

230. Describe one of the several classes of refrigera-
     ting machinery in use on board of ship. Several
     types exist, one being more economical than the rest:
     which is it?

231. Describe the defects to which the selected
     type is subject. How are the defects overcome?

232. How frequently are the parts opened out for
     examination? Name the parts.

233. How frequently are the condensers of re-
     frigerating plants opened for examination? How
     frequently are the coils tested by hydraulic pressure?
     On which side of the coil is corrosion most commonly
     found? Why should this be so?