994 REPORT— 1898. 



3. A New Instrument for Drawing Envelopes, and its Applicatioti to the 

 Teeth of Wheels and for other Purposes. By Professor H. S. Hele- 

 Shaw, LL.D., 3f. Inst. C.E.— See Reports, p. 6 19. 



4. Hydraulic Power Transmission hy Compressed Air. 

 By William George Walker, A.M.I.C.E., M.I.M.E. 



The air is compressed by tlie direct action of the falling water without the 

 aid of moving machinery. 



The compressor consists essentially of a head tank, a vertical down-flow pipe, 

 and a separating tank placed at the base of the down-flow pipe. The water may be 

 conveyed to the head tank by means of an open flume or pipe ; water entering the 

 down-flow pipe passes the ends of a number of small air pipes, from which air is 

 drawn in the form of small uniform globules, which, becoming entangled in the 

 descending water, are carried down to the air tank, where separation takes place, 

 the air rising to the top of the tank, and the water flowing out at the bottom and 

 up again outside the down-flow pipe to the tail race ; the difierence in height of the 

 tail race and pipe to head tank gives the available head of water. The globules of 

 air are uniformly compressed at constant temperature during their downward 

 path, the temperature of the water remaining practically constant. The amount 

 of compression of the air depends solely on the length of the down-pipe being 

 independent of available water-fall. 



A machine has been erected at Magog, Quebec a short distance from Montreal, 

 to drive the printing machinery of the Dominion Cotton Mills Company. It has 

 now been in operation over twelve months, running continuously night and day, 

 delivering dry compressed air, with an invariable pressure of 52 lbs. per square 

 inch. It provides power for six printing machines, each of which is driven by a 

 pair of engines with 8-inch by 12-iDch cylinders. The cotton mill proper uses 

 water-power, while the printing machines were formerly driven by steam, as 

 printing operations necessitate a very steady power and great variations in 

 speed, the engines varying from 20 to 300 revolutions per minute. Each has its 

 own engine, and in this case the air simply replaced steam, the same engines being 

 used without any modifications. 



The depth of the shaft is 128 feet, its size 6 feet by 10 feet, the down-flow pipe 

 is 3 feet 8 inches in diameter, the inverted tank at the bottom of the shaft is 17 

 feet by 18 feet. The penstock or in-flow pipe is 5 feet 6 inches in diameter, and in 

 the head-piece there are 30 air pipes, each 2 inches in diameter, and each having 

 32 air inlets at their base, making a total of 060 air inlets. Through these the air 

 mixes with the do'wn-flowing water, thus subdividing the air into an innumerable 

 number of small bubbles. The available working waterhead is 21 feet. By a 

 series of actual tests made by Professor McLeod, of McGill University, it was 

 shown that this plant gave an efficiency of 62 per cent, of the actual horse-power 

 of the water in dry cold air. 



This efficiency is secured notwithstanding that 20 per cent, of the air is lost by 

 insufficient separation, owing to the separating tank being a little too small, a 

 feature which may obviously be guarded against in future, so that an efficiency of 

 75 per cent, is considered as easily obtainable. The actual cost of installation of 

 such a plant is about 10/. per horse-power, although much depends on local con- 

 ditions, the price of labour, material, &c. The cost of sinking the shaft is the 

 principal item, so that larger plants can be installed at a much lower rate per 

 horse-power than small ones. 



5. Combined Electric Lighting and Power Plant for Docks and Harbours. 



By J. G. W. Aldridge. 



The introduction and development of hydraulic machinery by Armstrong 

 resulted in the equipment of almost every dock and harbour in the world with 



