Fig. 59.-DOUBLE-ACTING DUPLEX AMMONIA COMPRESSOR, DIRECTLY DRIVEN BY DUPLEX COMPOUND STEAM ENGINE. (Haslam Foundry & Engineering Co., Ltd.) Fig. 61.-ATMOSPHERIC CONDENSER FOR AMMONIA. The hot compressed gas passes through the pipes, and water trickles down over them, the liquefied gas being drawn off as formed by the junction pipes shown on the right. (Haslam Foundry & Engineering Co., Ltd.) rator, where the liquid expands to the gaseous condition. Very frequently also there is a brine tank, where a solution of calcium chloride is cooled, the brine being used to cool the chambers in which produce is stored, or the water from which ice is being made. The Refrigeration Circuit, with Compression. -The refrigeration circuit with the compression system, comprises the compressor, the condenser, and the evaporating coils. The compressor is a pump, which sucks in the gas that has done its work in the evaporator coils at each suction stroke, compresses it, and forces it on to the condenser at each compression stroke. Compressors are single-acting, or a certain part of the stroke, to perform the double office of lubricating the piston, and to fill the clearance space at the end of the cylinder, so that ammonia may not be left there after the compression stroke, the oil being pumped out afterwards. In all ammonia compression systems, the ammonia is passed through an oil separator, after it leaves the compressor, before it is used again. The Condenser.-The condenser is made in two forms-the submerged, in which the gas passes along pipes contained in a tank through which water is kept in continual circulation; and the atmospheric, Fig. 61, Plate III., in which the gas is also passed through pipes, but Fig. 60.-Double-Acting Haslam Ammonia Compression Cylinder, showing Suction and Delivery Valves at each end of the Cylinder, and Piston, with its Rod. double-acting. Single-acting compressors only draw in gas on one side of the piston, compressing it, and expelling it, on the same side of the piston, by the return stroke. In double-acting compressors, Figs. 59, Plate III., and 60, the gas is drawn in on both sides of the piston, and expelled on both sides, the gas entering behind the piston which is compressing,-on the opposite side. Lubrication is an important matter in connection with compressors, both of the piston and the bearings. For the latter, oil is maintained within the bearings under pressure from the cylinder itself, so that the ammonia shall not escape. In some forms of compressor oil is injected into the compressor cylinder, at the pipes are exposed to the action of the atmosphere, water continually dripping down over them, and some of the water evaporating as it trickles. This method is very efficient in warm climates, as the hotter the air, the larger the quantity of watery vapour it can accommodate. It is also very efficient in windy situations. The Evaporator, or Evaporating Coils.These are coils of pipe, made in different forms, through which the liquefied gas passes, and in which it is allowed to assume the gaseous form. The passage of the liquefied ammonia into the pipes is controlled by an expansion cock, something on the lines of a stop valve with steam, but with special arrangements. Where brine is used, the expansion coils are immersed in a tank through which the brine is kept in continual circulation, just as the water is with the submerged condenser; but the brine is brought back to the evaporating tank, after it has done its work in cooling the chamber. Absorption Apparatus.-The absorption apparatus consists of a generator, an absorber, an analyser, a rectifier, and an exchanger, see Fig. 62, Plate IV. In the latest forms of absorption apparatus, all of the above take the form of iron, or steel cylinders, in which pipes are enclosed. In the generator, steam passes through the pipes, raising the temperature of the ammoniacal solution surrounding them, and driving off the ammonia. The analyser is usually contained in the generator, and consists of baffle plates, gratings, and similar arrangements, designed GENERATOR REGULATING ABSORBER AMMONIA PUMP After passing through the evaporating coils, and performing its work there, the gas, as it has now again become, passes to the absorber, where it is again dissolved by water. There is a constant interchange between the generator and the absorber, of heat and liquid, see the diagram, Fig. 63. The generator requires as much heat as it can get; the absorber wants its temperature maintained as low as possible, in order that it may dissolve as much gas as possible. On the other hand, the solution of the gas in the water liberates heat. Further, there is considerable difference in the specific gravities of the strong and weak liquors. Advantage is taken of this latter fact, to cause a passage of weak liquor from the generator to the absorber, and of the stronger liquor, as it CONDENSER EXPANSION COOLER Fig. 63.-Diagram showing Arrangement of Ammonia Absorption Plant. The gas, it will be seen, passes from the generator to the condenser, then to the cooler (evaporator), then to the absorber, while there is an exchange of liquid between generator and absorber. to throw back any watery vapour that may be driven off with the ammonia. The ebullition of the water containing the ammonia in solution carries over minute quantities of water with the ammonia, very much in the way that watery vapour is carried over with the steam in steam boilers. Causing the mixture to impinge on the baffles, gratings, &c., condenses a portion of the watery vapour, and it runs back into the generator. A further portion is condensed in the rectifier, where it is subjected to the cooling action of water running through the pipes referred to above. The mixture of gas and water vapour is cooled sufficiently to condense the water vapour, but not the ammonia gas. Next the gas passes through the condenser, and thence to the evaporating coils, as with the compression system. is formed, from the absorber to the generator. The two streams pass through the exchanger, in pipes arranged for the purpose, the liquor from the generator that is on its way to the absorber giving up some of its heat to the liquor from the absorber that is on its way to the generator. In addition, the liquor on its way to the absorber is cooled by the aid of water, running in pipes, as described. One lot of water is used for all the above, passing in succession through the different apparatus. The absorption apparatus seems complicated, but in practice it is very simple. In the latest form the cylinders representing the different parts of the apparatus are mounted, two horizontally, side by side, and the remainder, one above the other vertically, the water and steam connections being easily made. A small pump for the ammonia, mounted on one of the cylinders, and fed with steam that has already done duty in the generator, completes the apparatus, except the evaporator, brine tank, &c. Ammonia is used very largely for refrigeration, because its latent heat of evaporation is so much greater than that of the other agents employed. Care must be taken in handling the apparatus, as the fumes are poisonous if present in only a very small percentage. When an escape occurs, with ammonia, the ground is the safest place, as the gas rises. Keep low, and dilute the gas with air, as quickly as possible. Ammonia does not explode, in the sense that petrol does, but if confined in a tank or other vessel, and subjected to great pressure, by heat, or from other causes, it may burst the vessel, with disastrous results. Ammoniac-Sal.-See Sal-Ammoniac. Ammunition.-See Projectiles. Ammunition Hoist.-See Hoists. Ampère. The unit of strength of electric current. A pressure of one volt will force one ampère through a resistance of one ohm. If this current is maintained for one second, one unit of electrical quantity is delivered, called the coulomb. See Electric Currents. Ampère Hour.-A convenient unit of electricity-the quantity of electricity delivered by a current of one ampère in one hour. See Electric Currents. when a white precipitate is thrown down on the addition of HCL to a solution it may be AgCL (argentic chloride), PbCL, (plumbic chloride), or Hg,CL (mercurous chloride). After precipitation the metal may be carefully weigheda process termed gravimetrical analysis. Volumetrical analysis is concerned with the measure instead of the balance, and determines the amount of the constituents in a solution by the use of standard solutions of oxidising agents, acids, or alkalies, combined with colour tests to show when the action is complete. Finally, the spectroscope may be called into use. The metal is volatilised, and the spectrum obtained gives an indication of the metal or metals present. Anastigmatic Lens.-This is the lens par excellence for the photography of machinery, machine tools, cranes, &c. It may be regarded as the ultimate development of the rapid Ampère Meter.-See Ammeter, the ab- rectilinear lens, and possesses in the highest breviated form now in use. Analysis, Chemical.-Chemical analysis may be either qualitative or quantitative. By qualitative analysis the chemist determines what substances are present in a compound; by quantitative analysis the relative proportions, weights or volumes of these constituents are ascertained. The former process, for example, will demonstrate that CO, is composed of carbon and oxygen, while the latter process shows that these two elements exist in the proportion of 12 parts of carbon to 15.96 x 2 or 31.92 parts of oxygen. When a compound substance is broken up into constituents which are themselves compounds we get an example of proximate analysis, while if these compounds are still further broken up into the elements composing them we speak of the process as ultimate analysis. As regards the methods of analysis the examination may be by means of the blowpipe, or by the use of certain reagents for qualitative analysis, and by gravimetrical, volumetrical, or spectroscopic analysis for quantitative analysis. Substances tested by the blowpipe are heated on a piece of charcoal, on platinum wire, fused with potassium nitrate, and so on. Or, the substance may be dissolved in water or acid, and by the addition of certain reagents, certain precipitates are thrown down. For instance, degree three qualities essential in engineering photography—(a) Flatness of field; (b) extreme covering power; (c) perfect definition. Chromatic and spherical aberration, astigmatism, inequality of illumination, distortion, and limitation of angle of view are all reduced to the minimum in these excellent lenses, so that in combination with a camera possessing a liberal range of movements the anastigmatic lens may be relied on in the most difficult cases. Its weakest point is in the lack of depth of definition, which has to be sacrificed to secure such a high speed. This, however, is easily remedied by working with a small stop. Another valuable feature about this type of lens is that it can be used on a plate larger than it is intended to cover when worked at a small aperture. It thus makes a good wide angle lens for use in cramped, confined positions. On the other hand, symmetrical or universal anastigmatics, as they are called, allow of each combination being used separately as a long focus lens, a quality useful when it is required to photograph small details in a machine or structure. Anchors. In ancient times, the anchor consisted merely of a weight, such as a large stone, with some arrangement for attaching a hemp cable to it. Later came the anchor with one arm, and no stock; then the anchor with |