2462

THE NEW ZEALAND GAZETTE.

[No. 58

156. What is the “cover” or “lap” of the valve ?
     What is its object? About what proportion of the
     stroke of the valve is it made?

157. What is the “exhaust cover” of a slide-
     valve? What is its effect upon cushioning and
     upon exhaust?

158. What is “minus cover” or “minus lap”
     on the exhaust? What is its effect upon the ex-
     haust and upon cushioning?

159. What is “cushioning” or “compression” in
     a steam-cylinder? How is it affected by the amount
     of cover or of minus cover there may be upon the
     exhaust? How is it affected by the exhaust pres-
     sure?

160. What is “mean effective pressure”? How
     is its amount ascertained?

161. What is a dial vacuum-gauge? What is its
     construction? For what is it used? About what
     amount should it show when the engine is working
     all right? What effect have the variations it indi-
     cates on the performance of the engine?

162. Does the vacuum-gauge enable you to tell
     what pressure there is in the condenser, or must
     you have recourse also to the barometer to arrive
     at that? How would you ascertain the actual
     amount of back pressure there is in the condenser?

163. What is a barometer? What is its construc-
     tion? Is a barometer sometimes used instead of
     a vacuum-gauge? In what respect does the weather
     barometer differ from the vacuum-gauge barometer?

164. The common vacuum-gauge and the common
     steam-gauge: In which of them are the graduations
     marked from atmospheric pressure? Does either of
     them tell what is the true actual pressure in the boiler
     or in the condenser?

165. Do steam and vacuum gauges vary with the
     variations of the weather barometer? When the
     weather barometer varies from 29 to 31, how much
     will the vacuum-gauge vary, and how will that affect
     the working of the engine? Why?

166. Vacuum is generally stated as so many
     inches: What is meant by, say, 20 inches vacuum?
     What does that tell us about the absolute pressure
     of the vapour then in the condenser?

167. From what depth will a pump draw water?
     Is there any limit? Why?

168. What is vacuum? Can vacuum move a
     piston? When the temperature of the water in the
     condenser is 212° F., what is the greatest degree of
     vacuum there can then be in the condenser?

169. What is a thermometer? What is its con-
     struction? What is the property of matter that is
     the principle of its construction? What tempera-
     tures are regularly noted by careful engineers?

170. What is the temperature of (1) melting ice,
     (2) of boiling water, (3) of steam about 60 lb. pressure
     by the steam-gauge, (4) of steam about 100 lb., and
     (5) of steam about 150 lb., also (6) of smoke in the
     funnel, and (7) of water in the hot well?

171. What is meant by the “conduction” of heat?
     Give examples of it in the boiler and in the engine.

172. What is meant by the “convection” of
     heat? Give examples of it in the boiler and in the
     engine.

173. What is meant by “radiation” of heat?
     Give examples of it in the boiler and in the engine.

174. Which is convection, which is radiation,
     and which is conduction in the following cases:
     (1) Heat from the glowing fuel to the furnace-crown,
     (2) heat passing from one side of the furnace-crown
     plate to the other, (3). heat passing from the steam-
     pipes in the engine-room, (4) the heat of evapora-
     tion?

175. What are the effective heating-surfaces of a
     marine boiler?

176. What parts of a marine engine are exposed to
     danger when the temperature is below freezing-
     point?

177. What precautions are necessary in cold
     climates when the temperature is below freezing-
     point?

178. State as many ways as you can by which a
     boiler might not get its full feed. A boiler, or one
     of a set of boilers, gets short of water although the
     feed-valve is open its proper amount: to what causes
     might this be due?

179. Of what are furnace-bars generally made?
     About what thickness are they at the top? About
     what space is between them? Whether are the
     bars put further apart for Newcastle coal or for
     Welsh coal?

180. Which burns faster, Newcastle coal or Welsh
     coal? Which is the flaming coal? Which makes
     most smoke?

181. About how many tons of steam-coal will be
     burnt per day in four furnaces, each 3 ft. wide and
     of about the usual length? On what grounds do
     you say so?

182. About how many tons of steam-coal will be
     burnt per day with good triple-expansion engines
     to drive an ordinary steamer of 40 ft. beam ten knots
     an hour by steam alone? On what grounds do
     you say so? What percentage more coal would be
     required to propel the same steamer one knot faster?

183. About how many tons of steam-coal will be
     burnt per day with a good triple-expansion engine,
     surface condensers, the low-pressure cylinder 60 in.
     diameter, doing average work? On what grounds
     do you say so?

184. A pair of inverted-cylinder direct-acting
     engines; there is a liner half an inch thick between
     the ahead eccentric-rod and the eccentric-strap; in
     overhauling the engine this piece is lost and for-
     gotten: what difference will its omission make in
     the working of the engine, on the admission, on the
     cut-off, and on the exhaust of the steam? Which
     will take place earlier and which later, distinguishing
     between the upstroke and the downstroke?

185. A pair of inverted-cylinder direct-acting
     engines driving a right-hand screw: on which of
     the cross-head guide-bars is the pressure greatest
     in the upstroke, and on which in the downstroke?

186. A screw propeller is getting loose, it has a
     little play on the shaft, sideways on the key or
     feather: how will this show in the engine-room?

187. How would you prove whether the centre
     line of the trunnions of an oscillating-cylinder be fair
     with the centre line of the main shaft?

188. How can the fairness of a line of screw-
     shafting be tested without lifting the shafts?

189. Where are steel forgings generally used in
     marine engines?

190. What is the composition of nickel steel?
     Where is it sometimes used in engines and boilers?

191. How is forced draught generated on board
     ship and supplied to boiler-furnaces? Is the air
     heated before delivery; if so, how?

192. What is “induced” draught? Compare the
     merits of “forced” and of “induced” draughts.

193. How is the intensity of forced or induced
     draught measured? What is the usual pressure
     employed in the mercantile marine?

194. An explosive gas is liberated from bunker
     coal; usually in well-ventilated bunkers this gas
     escapes into the atmosphere without doing harm; in
     ill-ventilated bunkers the gas, after mixing with a