Various

“ If we assume a large clearance space in the end of an air cylinder of a compressor which is furnishing air at a high pressure, we may readily conceive that space to be so large, and that pressure so high, that the entire volume of the cylinder would be filled by the air from the clearance space alone, and the compressor would take in no free air and would, of course, produce no compressed air. ”

“ A fly wheel does not furnish power, nor does it add to the economy of an engine except in so far as it enables it to cut off early in the stroke, and to equalize the power and resistance. In other words, a fly wheel is not a source of power, and in many cases it is only a means by which we accomplish rotative speed. It takes power to move matter, and assuming that other conditions are equal, every engine that carries a fly wheel that is larger than is necessary consumes a certain number of foot pounds in turning so much metal around through space. ”

“ In the cylinder of an air compressor the energy of the piston is converted into molecular motion in the air and the result, or the equivalent, is heat. A higher temperature means an increased speed of vibration, and a lower temperature means that this speed of vibration is reduced. If I hold an open cylinder in my left hand and a piston in my right, and place the piston within the cylinder, I here have a confined volume of air at the temperature and the pressure of this room. These particles of air are in motion and produce heat and pressure in proportion to that motion. ”

“ But the price of coal gas seemed to be too high for use in these large engines, in which sizes steam is comparatively cheap; and so poorer gas, which, though possessing only about 28 per cent. of the heating power, is still cheaper in proportion than coal gas, when it is made on the spot, was introduced to tide over the difficulty. Difficulties have been successively overcome, with the result which we have just seen, namely, 1.37 pounds of anthracite per effective horse power, or about half the carbon which a steam engine of the same power of excellent design, and well kept up, would consume. ”

“ Water is not a good conductor of heat. In this case only one side of a large body of air is exposed to a water surface, and as water is a bad conductor, the result is that a thin film of water gets hot in the early stage of the stroke and little or no cooling takes place thereafter. The compressed air is doubtless cooled before it gets even as far as the receiver, because so much water is tumbled over into the pipes with it, but to produce economical results the cooling should take place during compression. ”

“ In a northern climate the length of the days in summer, and the natural dryness of the air, compensate in some measure the reduction of temperature, and mature the plant only to the extent sufficient for the purpose for which it is grown. Perhaps the suspension of vital action during winter, which must be more complete in northern latitudes, as our frosts are more severe, tends to preserve certain plants, native of the south, for it is observed that all plants are more sensitive to cold when vegetation is active than when it is at rest. ”

“ When the pressure of the air gets above the desired point in the receiver, the valve is lifted and the air is exhausted from behind the discharge valves, thus letting the compressed air at full receiver pressure into the cylinder at both ends, and balancing the engine. At the same instant the compressed air is exhausted from the little piston connected with the balanced steam valve and the steam is automatically throttled, so that only enough steam is admitted to keep the engine turning around, or to overcome the friction, no work being done. ”

“ It has been demonstrated by experiments made in France that the power required to compress moist air is less than that for dry air. A table showing the power required to compress moist and dry air has been prepared from the data of M. Mallard and shows that for five atmospheres the work expended in compressing one pound of dry air is 58,500 foot pounds, while that for moist air is 52,500 foot pounds. In expansion also moisture in the air adds to the economy, but in both cases the saving of power is not great enough to compensate for the many disadvantages due to the presence of water. ”

“ By far the most serious obstacle to water injection, and that which condemns the wet compressor, is the influence of the injected water upon the air cylinder and parts. Even when pure water is used, the cylinders wear to such an extent as to produce leakage and to require reboring. The limitation to the speed of a compressor is also an important objection. The claim made by some that the injected water does not fill the clearance spaces, but is aerated, does not hold good, except with an inefficient injection system. ”

“ The progress that has been made during the last twenty years in the thermatic study and construction of gas motors (without speaking of hot air motors) has shown that the use of steam is not absolutely indispensable for the production of work, and it has demonstrated that, as regards dynamic product, the gas motor preserves the advantage, although the relatively high price of the illuminating gas employed in the production of the motive power generally renders the use of this combustible more costly than steam, especially for high powers. ”

“ We fill our rooms with imitations of somber Spanish leather, stain and paint our woodwork in leathery and muddy tones, to arrive at what is now a sort of decorator's god. Quaintness is the name of that god. ”

“ Up to recent years there was no reason for putting the question that forms the title of this article, for it was admitted by all that the conversion of thermic energy, or heat produced by the combustion of coal, into mechanical energy or work could no longer be effected economically except by having recourse to steam. In ordinary language, and even to manufacturers, steam engine was the equivalent of thermic motor, and it would not have occurred to any one to use anything else but steam to effect the transformation. ”

“ The steam engine uses coal, the producer requires English anthracite, which is dearer; the gas motor uses a great deal of water and a great deal of oil, which cost money; and gas motors are dear, while gas producers and their adjuncts cost a tidy bit of money, and wear out pretty fast. Is not steam, after all, more economical in the long run? Besides, producers are bulky and take up a great deal of space; the weight of fuel is only one element in a complicated problem. ”

“ The most useful and convenient sizes for power purposes are from 10 to 20 feet, and from 2 to 20 feet wide, although, as before stated, there is scarcely a limit under 100 feet diameter for special purposes.
In designing this class of wheels special attention should be given to the concentration and increase of the velocity of the current by wing dams or by the narrowing of shallow streams; always bearing in mind that any increase in the velocity of the current is economy in increased power, as well as in the size and cost of a wheel for a given power. ”

“ It is obvious that cost of construction and maintenance have much to do with the commercial value of an air compressor. The hydraulic piston machine not only costs a great deal more in proportion to the power it produces, but it costs more to maintain it, and it costs more to run it. ”

“ The gas generator requires the use of English anthracite, while a steam boiler is heated with any kind of coal. The prices of unity of weight are therefore very different. Moreover, the gas motor necessitates an immense amount of water for the washing of the gas and the cooling of the cylinder, through circulation in the jacket. It is well to keep this fact in view. On another hand, the lubrification of the cylinders requires a profusion of oil whose flashing point must be at a very high temperature, else it would burn at every explosion and fill the cylinder with coom. ”

“ A well constructed steam engine, carefully kept in repair and as much improved as it is possible to make it, would certainly consume twice as much coal to produce the same quantity of effective work, say at least 1,200 grammes per horse hour. But, as has been objected with reason, it does not suffice to compare the figures as to the consumption of fuel in order to institute a serious comparison between the steam engine and the motor using poor gas. ”

“ On the contrary, it is a most fallacious system, because it introduces all the disadvantages of water injection without its isothermal influence. Water, by mere surface contact with air, takes up but little heat, while the air, having a chance to increase its temperature, absorbs water through the affinity of air for moisture, and thus carries over a volume of saturated hot air into the receiver and pipes, which on cooling, as it always does in transit to the mine, deposits its moisture and gives trouble through water and freezing. ”

“ The heat of compression is so thoroughly absorbed that the thermal loss is only 1.6 per cent.; but the loss by friction of the engine is 14.5 per cent., and the net economy of the whole system is no greater than that of the best American dry compressor, which loses about one-half the theoretical loss due to heat of compression, but which makes up the difference by a low friction loss. ”