THE WORK OF THE FUTURE.
The deciphering of this wonderfully intricate constitution of the heavens would be undoubtedly one of the chief astronomical works of the coming century. The primary task of the sun's motion in space, together with the motions of the brighter stars, had been already put well within our reach by the spectroscopic method of the measurement of star motions in the line of sight. Astronomy, the oldest of the sciences, had more than renewed her youth. At no time in the past had she been so bright with unbounded aspirations and hopes. Never were her temples so numerous, nor the crowd of her votaries so great.
The British Astronomical Association formed within the year numbered already about 600 members. Happy was the lot of those who were still on the eastern side of life's meridian! Already, alas! the original founders of the newer methods were falling out—Kirchhoff, Angstrom, D'Arrest, Secchi, Draper, Becquerel; but their places were more than filled; the pace of the race was gaining, but the goal was not and never would be in sight. Since the time of Newton our knowledge of the phenomena of nature had wonderfully increased, but man asked perhaps more earnestly now than in his days, what was the ultimate reality behind the reality of the perceptions? Were they only the pebbles of the beach with which we had been playing? Did not the ocean of ultimate reality and truth lie beyond?
Presidential address before the British Association, Cardiff, 1891.
CLIMATIC CHANGES IN THE SOUTHERN HEMISPHERE.
By C.A.M. TABER.
Having had occasion to cruise a considerable time over the Southern Ocean, I have had my attention directed to its prevailing winds and currents, and the way in which they affect its temperature, and also to the ice-worn appearance of its isolated lands.
It is now generally conceded that the lands situated in the high latitudes of the southern hemisphere have in the remote past been covered with ice sheets, similar to the lands which lie within the antarctic circle. The shores of Southern Chile, from latitude 40° to Cape Horn, show convincing evidence of having been overrun by heavy glaciers, which scoured out the numerous deep channels that separate the Patagonian coast from its islands. The Falkland Islands and South Georgia abound with deep friths; New Zealand and Kerguelen Land also exhibit the same evidence of having been ice-laden regions; and it is said that the southern lands of Africa and Australia show that ice accumulated at one time to a considerable extent on their shores. At this date we find the southern ice sheets mostly confined to regions within the antarctic circle; still the lands of Chile, South Georgia, and New Zealand possess glaciers reaching the low lands, which are probably growing in bulk; for it appears that the antarctic cold is slowly on the increase, and the reasons for its increase are the same as the causes which brought about the frigid period which overran with ice all lands situated in the high southern latitudes.
Why there should be a slow increase of cold on this portion of the globe is because of the independent circulation of the waters of the Southern Ocean. The strong westerly winds of the southern latitudes are constantly blowing the surface waters of the sea from west to east around the globe. This causes an effectual barrier, which the warm tropical currents cannot penetrate to any great extent. For instance, the tropical waters of the high ocean levels, which lie abreast Brazil in the Atlantic and the east coast of Africa in the Indian Ocean, are not attracted far into the southern sea, because the surface waters of the latter sea are blown by the westerly winds from west to east around the globe. Consequently the tropical waters moving southward are turned away by the prevailing winds and currents from entering the Southern Ocean. Thus the ice is accumulating on its lands, and the temperature of its waters slowly falling through their contact with the increasing ice; and such conditions will continue until the lands of the high southern latitudes are again covered with glaciers, and a southern ice period perfected. But while this gathering of ice is being brought about, the antarctic continent, now nearly covered with an ice sheet, will, through the extension of glaciers out into its shallow waters, cover a larger area than now; for where the waters are shoal the growing glaciers, resting on a firm bottom, will advance into the sea, and this advancement will continue wherever the shallow waters extend. Especially will this be the case where the snowfall is great.
Under such conditions, it appears that the only extensive body of shallow water extending from the ice-clad southern continent is the shoal channel which separates the South Shetlands from Cape Horn, which is a region of great snowfall. Therefore, should the antarctic ice gain sufficient thickness to rest on the bottom of this shallow sea, it would move into the Cape Horn channel, and eventually close it. The ice growth would not be entirely from the southern continent, but also from lands in the region of Cape Horn. Thus the antarctic continent and South America would be connected by an isthmus of ice, and consequently the independent circulation of the Southern Ocean arrested. Hence it will be seen that the westerly winds, instead of blowing the surface waters of the Southern Ocean constantly around the globe, as they are known to do to-day, would instead blow the surface waters away from the easterly side of the ice-formed isthmus, which would cause a low sea level along its Atlantic side, and this low sea level would attract the tropical waters from their high level against Brazil well into the southern seas, and so wash the antarctic continent to the eastward of the South Shetlands.
The tropical waters thus attracted southward would be cooler than the tropical waters of to-day, owing to the great extension of cold in the southern latitudes. Still they would begin the slow process of raising the temperature of the Southern Ocean, and would in time melt the ice in all southern lands. Not only the Brazil currents would penetrate the southern seas, as we have shown, but also the waters from the high level of the tropical Indian Ocean which now pass down the Mozambique Channel would reach a much higher latitude than now.
The ice-made isthmus uniting South America to the antarctic continent would on account of its location be the last body of ice to melt from the southern hemisphere, it being situated to windward of the tropical currents and also in a region where the fall of snow is great; yet it would eventually melt away, and the independent circulation of the Southern Ocean again be established. But it would require a long time for ice sheets to again form on southern lands, because of the lack of icebergs to cool the southern waters. Still, their temperature would gradually lower with the exclusion of the tropical waters, and consequently ice would slowly gather on the antarctic lands.
The above theory thus briefly presented to account for the climatic changes of the high southern latitudes is in full accord with the simple workings of nature as carried on to-day; and it is probable that the formation of continents and oceans, as well as the earth's motions in its path around the sun, have met with little change since the cold era iced the lands of the high latitudes.
At an early age, previous to the appearance of frigid periods, the ocean waters of the high latitudes probably did not possess an independent circulation sufficient to lower the temperature so that glaciers could form. This may have been owing to the shallow sea bottom south of Cape Horn having been above the surface of the water, the channel having since been formed by a comparatively small change in the ocean's level. For, while considering this subject, it is well to keep in mind that whenever the western continent extended to the antarctic circle it prevented the independent circulation of the Southern Ocean waters, consequently during such times ice periods could not have occurred in the southern hemisphere.
It will be noticed that according to the views given above, the several theories which have been published to account for great climatic changes neglect to set forth the only efficacious methods through which nature works for conveying and withdrawing tropical heat sufficient to cause temperate and frigid periods in the high latitudes. While lack of space forbids an explanation of the causes which would perfect an ice period in the northern hemisphere, I will say that it could be mainly brought about through the independent circulation of the arctic waters, which now largely prevent the tropical waters of the North Atlantic from entering the arctic seas, thus causing the accumulation of ice sheets on Greenland. But before a northern ice period can be perfected, it seems that it will need to co-operate with a cold period in the southern hemisphere; and in order to have the ice of a northern frigid period melt away, it would require the assistance of a mild climate in the high southern latitudes.—Science.
AMMONIA.
In the majority of refrigerating and ice machines ammonia gas is the substance used for producing the refrigeration, although there are other machines in which other material is employed, one of these being anhydrous sulphurous acid, which is also a gas. Ammonia of itself is a colorless gas, but little more than one half as heavy as air. In its composition ammonia consists of two gases, nitrogen and hydrogen, in the proportion by weight of one part nitrogen and three parts hydrogen. The gas hydrogen is one of the constituents of water and is highly inflammable in the presence of air or oxygen, while the other component of ammonia, nitrogen, forms the bulk or about four-fifths of the atmosphere. Nitrogen by itself is an inert gas, colorless and uninflammable. Ammonia, although composed of more than three-fourths its weight of hydrogen, is not inflammable in air, on account of its combination with the nitrogen. This combination, it will be understood, is not a simple mixture, but the two gases are chemically combined, forming a new substance which has characteristics and properties entirely different from either of the gases entering into its composition when taken alone or when simply mixed together without chemical combustion. Ammonia cannot be produced by the direct combination of these elements, but it has been found that it is sometimes made or produced in a very extraordinary manner, which goes to show that there is yet considerable to be learned in regard to the chemistry of ammonia. Animal or vegetable substances when putrefying or suffering destructive distillation almost invariably give rise to an abundant production of this substance.
The common method for the manufacture of ammonia is to produce it from the salt known as sal-ammoniac. Sal-ammoniac as a crystal is obtained in various ways, principally from the ammoniacal liquor of gas works, also from the condensed products of the distillation of bones and other animal refuse in the preparation of animal charcoal, and which is of a highly alkaline nature. This liquid is then treated with a slight excess of muriatic acid to neutralize the free alkali, and at the same time the carbonates and sulphides are decomposed with the evolution of carbonic acid and sulphureted hydrogen. All animal matter, the meat, bones, etc., contain considerable carbon, while the nitrogen from which the ammonia is produced forms a smaller portion of the substance. The object is then to get rid of the carbon and sulphur, leaving the nitrogen to combine, through chemical affinity, with a portion of the hydrogen of the water, the oxygen which is set free going to form the carbonic acid by combining with the carbon. The liquor after being neutralized is evaporated to dryness, leaving a crystallized salt containing a portion of tarry matter.
The salt is then purified by sublimation, that is, it is heated in a closed iron vessel until it is transformed into a gas which separates and leaves, in a carbonized state, all foreign substance. After this gas is cooled, it condenses and again forms crystals which are in a much purer condition. If necessary to further purify it, it is again sublimed. The iron vessels in which the sublimation takes place are lined with clay and covered with lead. The clay lining and lead covering are necessary, for if the gas evolved during the process of sublimation came in contact with the iron surface, the gas would be contaminated and the iron corroded. Sublimed sal-ammoniac has a fibrous texture and is tough and difficult to powder. It has a sharp, salty taste and is soluble in two and a half parts of cold and in a much smaller quantity of hot water. During the process of sublimation the ammonia is not decomposed. But there are several ways in which the gas may be decomposed, and a certain portion of it is decomposed in the ordinary use of it in refrigerating machines. If electric sparks are passed through the gas, it suffers decomposition, the nitrogen and hydrogen then being in the condition of a simple mixture. When decomposed in this manner, the volume of the gas is doubled and the proportion is found to be three measures of hydrogen to one of nitrogen, while the weight of the two constituents is in the proportion of three parts hydrogen to fourteen of nitrogen.
The ammonia gas may also be decomposed by passing through a red hot tube, and the presence of heated iron causes a slight degree of decomposition. This sal-ammoniac is powdered and mixed with moist slaked lime and then gently heated in a flask, when a large quantity of gaseous ammonia is disengaged. The gas must be collected over mercury or by displacement. The gas thus produced has a strong, pungent odor, as can easily be determined by any one working around the ammonia ice or refrigerating machines, for as our friend, Otto Luhr, says, "It is the worst stuff I ever smelled in my life." The gas is highly alkaline and combines readily with acids, completely neutralizing them, and the aqua ammonia is one of the best substances to put on a place burned by sulphuric acid, as has been learned by those working with that substance, for although aqua ammonia of full strength is highly corrosive and of itself will blister the flesh, yet when used to neutralize the effect of a burn from sulphuric acid its great affinity for the acid prevents it from injuring the skin under such conditions.
The distilled gas, such as has just been described, is the anhydrous ammonia used in the compressor system of refrigeration, while it is the aqua ammonia that is used in the absorption system of refrigeration. Aqua ammonia or liquor ammonia is formed by dissolving the ammonia gas in water. One volume of water will dissolve seven hundred times its bulk of this gas, and is then known as aqua ammonia, in contradistinction to anhydrous ammonia, the latter designating term meaning without water, while the term aqua is the Latin word for water.
Anhydrous ammonia, the gas, may be reduced to the liquid form at ordinary temperatures when submitted to a pressure of about 95 pounds. During the process of liquefaction the ammonia gives up a large amount of heat, which if absorbed or radiated while the ammonia is in the liquid condition, the gas when allowed to expand will absorb from its surroundings an amount of heat equal to that radiated, producing a very great lowering of temperature. It is this principle that is utilized in refrigeration and ice making. In the absorption system, where aqua ammonia is used, the liquor is contained in a retort to which heat is applied by means of a steam coil, and a great part of the gas which was held in solution by the water is expelled, and carries with it a small amount of water or vapor. This passes into a separator in the top of a condenser, from which the water returns again to the retort, the ammonia gas, under considerable pressure, passing into the coolers. These are large receptacles in which the gas is permitted to expand. By such expansion heat is absorbed and the temperature of the surroundings is lowered. From the coolers the gas returns to the absorber, from which it is pumped, in liquid form, into the retort, to be again heated, the gas expelled and the process repeated. As the gas passes through the different processes, being heated under pressure, cooled, expanded again, more or less decomposition takes place, presumably from a combination of a small portion of the nitrogen with vegetable, animal, or mineral matter that finds its way into the system. Such decomposition, with the loss of nitrogen, leaves a small portion of free hydrogen, which is the gas that can be drawn from the top of the absorber, ignited and burned. The presence of hydrogen gas in the absorber is not necessarily detrimental to the effectiveness of the system, but as hydrogen does not possess the qualities of absorbing heat in the same way and to the same extent as ammonia, the presence of hydrogen makes the operation of the apparatus somewhat less efficient.—Stationary Engineer.
The refrigerating apparatus illustrated and described in the SCIENTIFIC AMERICAN SUPPLEMENT of June 25, No. 812, is substantially that patented by Messrs. Erny, Subers & Hoos, of Philadelphia. The illustration was copied from their patents of November and February last.