June 20.] THE NEW ZEALAND GAZETTE. 1887

131. At what part of a screw-steamer is the pressure that propels it applied to the hull?

132. At what part of a paddle-steamer is the pressure that propels it applied to the hull?

133. About how much fuel per indicated horsepower per hour is required by modern steam-engines, common, compound, and triple expansion?

134. What is the explanation of the economy of the surface condenser?

135. What is the construction of a surface condenser? Of what are its tubes made? How are they fixed? How are they kept tight? What is done with a split tube?

136. Where do surface condensers foul? How are they cleaned?

137. What non-conducting substances are employed to prevent radiation, and how are they applied?

138. In the construction of smoke-box doors and of dry uptakes, what provision is made to lessen the amount of radiation?

139. How can the formation of black smoke be prevented? Describe smoke-preventing apparatus.

140. What is meant by “circulation” in a boiler, and what are the results of defective circulation?

141. What means are sometimes adopted to improve the circulation in a boiler?

142. By what arrangement is the circulation promoted in a “hay-stack” boiler?

143. Describe a ship’s side air-pump discharge-valve. In what respects does it sometimes differ from a common stop-valve, and what attention does it require?

144. What is the construction of a feed escape-valve, to what is its discharge connected, and how is its loading regulated? Where should the escaping water flow?

145. When there is no feed escape-valve, what is the arrangement of the feed valves or cocks?

146. What is the measure of a horse-power? How is indicated horse-power ascertained?

147. Has “nominal horse-power” a fixed meaning? What is the use of this expression? What is generally taken as the measure of 1-horse power nominal?

148. What is “back pressure” in a cylinder? About how much is it in each of the cylinders in your last steamer? Is excessive cushioning ever a trouble under certain conditions in modern engines? Say when and why and in which cylinder this occurs.

149. What is meant by “speed of piston”? About how much is the speed of piston in modern marine engines?

150. What is “atmospheric pressure”? What is its average amount? What instrument tells this amount?

151. What is “gross pressure” or “absolute pressure”? What pressure is it that is shown by steam-gauge?

152. What is meant by “cutting off” steam? How is it done? What part of the valve regulates the cut-off?

153. What is a piston slide-valve? Describe its construction. Why are such frequently employed in place of the common slide-valve? What is a great drawback to the use of these valves?

154. What fixes the time of closing the exhaust? After the exhaust is closed and before the port opens for steam, what becomes of the steam that is in the cylinder?

155. What is the “lead” of the valve? What is its object? About what amount is it?

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 exhaust 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 pressure?

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 has the variations it indicates 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 construction? 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 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 effect 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°, what is the greatest degree of vacuum there can then be in the condenser?

169. What is a thermometer? Its construction? What is the property of matter that is the principle of its construction? What temperatures 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,