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be passed through 1,000 ft. of pipes, the loss of pressure of airfor 2|in., 3in., 3^-in. and 4 in. pipes would be 5f lb., 2 lb., 1-J-lb. respectively. Leakage at the joints through the expansion and contraction of the pipes is a fruitful and at times a serious loss of power. A receiver of suitable size should always be placed alongside the compressor, and where a considerable length of pipes is used it is an advantage to have a receiver as near the motor as practicable. (5.) Method of using Compressed Air. When air is compressed it is heated, and when it expands it is cooled. The latter fact gives rise to the inconvenience so frequently met with in air-motors of ice being formed in the ports through the freezing of the moisture in the air. Where the air is admitted to the motor, practically during the whole stroke there is little danger of ice being formed, but there is a terrific waste of power, for it is as important for economy to use air expansively as it is to use steam expansively. While a little moisture in air used expansively results in the formation of ice in the ports, it may be pointed out that aqueous vapour has a specific heat nearly double that of air, and consequently cools less rapidly under expansion than dry air, and the tendency of an excess of moisture is to reduce the cooling. The specific heat of water being still greater, a spray of water may be effectively used in the motor-cylinder to prevent cooling to the freezing-point. The writer was familiar many years ago with an instance where, in the case of large haulage-engines placed underground, the inconvenience caused by freezing was so serious that compressed air was abandoned, and steam, though inconvenient, was substituted. Reheating the air is, however, the most effective method of allowing air to be used expansively without the formation of ice in the ports, and this can best be done by passing the air near the motor through a coil of pipes heated by a small furnace; and a further elaboration, permitting the highest degree of expansion, is affected by introducing a small quantity of water into the heater, where it is converted into steam. A move in the latter direction was made years ago, by the use of a jet of steam in the air-pipe near the motor. In practice it is found that reheating the air not only prevents freezing, but results in a very great economy in the use of compressed air, at a small cost both for plant and fuel. (6.) Dangers attending its Use. These are so slight as to be scarcely worth considering, but their existence is worthy of passing notice. A few cases are known where an explosion, more or less marked, has occurred in the receiver placed near the compressor. In these instances combustion has been set up apparently in the carbonaceous matter deposited from the lubricants used in the compressor. The readiness with which a piece of old oily waste takes fire at comparatively low temperature is well known, and it is possible that a similar action may take place in the deposited carbon if subjected accidentally to abnormal heating by a failure in the cooling apparatus of the compressor. The use of compressed air seems at first sight an extremely simple one, and consequently the principles surrounding its use are seldom inquired into. The results obtained from it are, in consequence, at times appallingly poor, and its reputation as a means of transmitting power suffer proportionately. In the worst forms of machines 10 per cent, only of the power expended may be obtained, and the writer has a distinct recollection of the care with which his Belgian professor demonstrated the impossibility of obtaining more than 33 per cent, of useful effect from compressed air. But to quote from Professor Goodman: "In the best cases, without reheating about 55 per cent., and with reheating 75 per cent., of the total power is given out by the motor." The extensive use made of compressed air in metalliferous mines, particularly for rock drills, should naturally induce an intelligent interest in its use in the Australasian Colonies, and a discrimination in the proper and improper methods of employing it.

In the following appendix will be found the annual reports of Inspectors of Mines, Wardens and other officers; the questions used at the recent examinations of candidates for certificates of competency as mine-managers and battery-superintendents, together with a list of persons holding such certificates ; and the usual schedules. I have, Ac, John Hayes, The Hon. the Minister of Mines. Inspecting Engineer.