SCIENCE, MECHANICAL INVENTIONS, ETC

New Zealand Herald, Volume XXXVII, Issue 11544, 1 December 1900, Page 6 (Supplement)

SCIENCE, MECHANICAL INVENTIONS, ETC

MECHANICAL STOKING. Among the signs of the times in the world of steam engineering is (remarks a writer in a New York scientific weekly) a wonderful' growth during the past decade of mechanical stoking. Not merely is this scientific method of firing being adopted for isolated steam plants of moderate capacity, but mechanical stoking has come to be regarded as a sine qua non in the equipment of a large modern power station. Just how extensive has been the growth of this industry may be judged from the fact that one firm alone in this city are now installing mechanical stokers for a total of 66,000 horsepower of boilers, while they are, furthermore, equipping over 226,000 horse-power of boilers in various parts of the United States. These figures are practically striking when we bear in mind that at the commencement of this decade there were only three mechanical stokers manufactured in this country. Equally curious is the fact that although the application of this, industry on a large scale in this country is of such recent date, mechanical stoking, as such, is as old as the steam engine itself. The earliest records of this subject show that the first mechanical stoker to be patented was one designed by the inventor of the steam engine himself, and it is to the credit of James Watt that the design, crude as it may have been, embodies the essential features of any 'good mechanical stoker. The coal, was "fed at the furnace door, and as it became coked was pushed back over two sets of horizontal grate bars. At the front of the furnace it became coked, and the gases from the coking fuel passed over the partially - coked and live fuel in the middle and at the back of the grate, where they were completely consumed. Such, in principle at least, is the mechanical stoker of to-day. The popularity of mechanical stoking is to be set down to the relative obvious advantages over stoking by hand. In the first place, the feeding of the fuel is constant and even.- The fresh fuel being introduced only at the front of the furnace is very gradually coked, the liberated gases meeting with a supply of fresh air led in by special ducts to provide the necessary oxygen for combustion, and the bed of incandescent fuel over which the gases pass serves to raise their temperature to the ignition point and secure their perfect combustion. A further advantage is the ease with which a bed of fuel of uniform thickness may be maintained over the whole grate surface. Furthermore, there is the prevention of a serious loss of heat due to the necessarily frequent opening of the fire doors in hand-firing. SCREWS. The smallest screws in the world are made in a watch factory. They are cut from steel wire by a machine; but as the chips fall from the knife it looks as if the operator were simply cutting up the wire for fun. One thing is certain, no screws can be seen, and yet a screw is made every third opera* tion. The fourth jewel wheel screw is next to invisible, and to the naked eye it looks like dust. With a glass, however, it is seen to be a small screw, with 260 threads to an inch, and with a very fine glass the threads may be seen clearly. These little screws are four one-thousandths of an inch in diameter, and the heads are double in size. It is estimated that an ordinary lady's thimble would hold 10.000 of them. About a million are made in a month, but no attempt is ever made to count In determining the number. 100 of them are placed on a very delicate balance, and the number of the whole amount is calculated from the weight of this. All the small parts of the watch are counted in this way, probably 50 out of the 120. After being cut, the screws are hardened and put in frames, about 100 to the frame, head up. This is done very rapidly, but entirely by the sense of touch instead of by sight, so that a blind man could do it as well as the owner of the sharpest eye. The heads are then polished in an automatic machine, 10,000 at a time. The plate on which they are polished is covered with oil and a grinding compound, and on this the machine moves them very rapidly by a reversing motion until they are perfectly polished. MOUNTING PHOTOGRAPHIC PRINTS. To prevent photographic prints from curving when dry, a paste must be used containing as little water as possible. The following formula is recommended : Gelatine, 2 parts; water, 4 parts; alcohol, 8 parts. The alcohol is added slowly as soon as the gelatine is well dissolved in the water, and the vessel turned continually to obtain a homogeneous mixture. The solution must be kept hot during the operation on a water bath, and should be applied quicklv. as it soon dries ; the print must be placed exactly the first time, as it adheres at once. The solution keeps for a long time in well-corked bottles. PPOTHJCTION of glossy cement. The subject of an invention by Wilhelm Borgolte, of Hoexterf, Germany, is the production of a new peculiar cement, which is said to excel Portland cement, not only in being much more resistive to atmospheric carbonic acid and moisture, but also in forming an extremely hard mass with mirrorlike lustre upon setting. The product prepared according to the process described below adheres, mixed with water, in a superior manner and possesses a certain resistance to diluted acids. For the building trades it is of importance that the new cement has the property or accepting in a freshly set state, without special preparation, durable oil paint and other coating. The process consists in first burning the raw materials suitable for the manufacture of cement singly with difficultly decomposable hydrocarbons and exclusion of air, before the production of the raw mixture of the cement. The substances thus treated, which have a black or dark grey appearance owing to embedded graphite, are powdered and in the requisite mixing proportions burnt once more with addition of oil and powdered coal and exclusion of air. It has been proposed before to mix and burn cement with hydrocarbons, but the novelty and peculiarity of the present method consist in the burning with exclusion of air, as well as in that the materials, converted by the first burning process, are burned again, and act upon each other at the second baking, so that a product with new chemical and physical properties results. While a cement which has been burned only once, with admixture of hydrocarbons and exclusions of air, shows rust like brown spots upon continued storing in damp air, same do not appear if the raw material has singly been subjected to the above described pre-burning. By the first baking of the raw materials a material change sets in, so that ferric oxide is reduced and lime does no longer slake in water with calefaction. The second burning causes the real formation of cement. In carrying out the process, the raw materials to be burned are separately reduced to powder and singly mixed with' two percentum bv weight of'difficultry decomposable hydrocarbons. The various mixtures are, after addition of water, shaped into bricks, which are baked with exclusion of air, as far as possible, after drying. The burnt product is reduced and ground like the Portland cement clinkers. It has been established by trials that the raw materials thus burned and ground furnished an especially good gloss-cement, for instance, in the following: —Limestone, 2 parts, by weight; clay, 1 part, by weight; clayey marl, 1 part, by weight; argillaceous earth, 1 part, by weight; ground coal, 1 part, by weight. To the intimate mixture of the above ingredients, the raw powder proper, another 2 per cent, of liquid hydrocarbons is added. After the whole has been homogenised into a stiff mass with addition of water, like in the manufacture of Portland cement, it is shaped into bricks, which, after drying, are burned with exclusion or air contrary to the practice pursued in the manufacture of Portland cement. The burnt product is further treated like Portland cement. If other raw materials are employed, the raw mixture should be altered accordingly. The lustrous cement thus obtained is mixed with unburnt materials according to the purpose it is to be used for. The "following mixing ratio has been found valuable for casting and stamping purposes: — Gloss cement, 2 parts; crude clay, powdered, 2 parts; clayey marl, powdered, 1 part; sandstone, powdered, 1 part; Micaceous slate marl, powdered, 2 parts; , sandgated sandstone, powdered, 2 parts; sandcoal cinders, 2 parts..