the exact details. Finke (Oesterlen's Handb. der Hygiene, 2d edit., 1857) also states that in Hungary and Holland marsh-water is daily taken without injury.-(PARKES.) The inhalation of the fumes of oxide of zinc appears to produce a variety of ague, termed by Thackrah "brass ague," and by Dr. Greenhow brassfounders' ague," to which workers in this metal are subject. The symptoms are tightness and oppression of the chest, with indefinite nervous sensations, followed by shivering, an indistinct hot stage, and profuse sweating. These attacks are not periodical. It may be doubted whether the malarious poison is in the form of a gas, for the observations of microscopical observers show the extreme minuteness of the germs of disease: they are probably not more than of an inch in size, and it is highly probable that the real cause of ague is the entry into the blood of some low forms of spores of fungi, or of some minute animalcules. Ague is always to be found where fungi grow, and is always associated with great impurity of what Pettenkofer calls "the ground-air"-that is, the air contained in the interstices of the soil, no inconsiderable volume of which is drawn into every house which has a fire on the floor which rests on the earth. That animalcules, &c., may exist in the blood is proved by the wonderful discovery by Dr. Lewis (see FILARIA) of hairlike worms in the circulation; and in considering this point, we should bear in mind that the remedial agents employed to check aguequinine, arsenic, &c.-are drugs capable of destroying animal life, and it is possible that they exercise a beneficial effect by destroying these spores or animalcules. Thorough and efficient drainage—and it must be remembered that drainage purifies both the ground-air and the ground-water-and good water, free from vegetable contamination, are the most satisfactory means employed to drive malarial fevers from a district; and that these means may be employed with certainty of success is proved by the fact that during the last two hundred years cases of ague have in this country been greatly on the decrease, as good drainage has become more general and perfect, and as-speaking generally-the supply of water to the houses has greatly improved, both in quality and quantity, so the number of patients suffering from paludal poisoning has steadily diminished. We are reminded of the prevalence of intermittent fevers two centuries ago by the wellknown words of Oliver Cromwell-himself a victim to ague-"Matrem pietissimam, fratres, sorores, servos, ancillas, nutrices, conductitias, quotquot erant intra eosdem nobiscum parietes, ac fere omnes ejusdem ac vicinorum pagorum incolas, hoc veneno infectos et decumbentes vidi." And when we remember that the country surrounding London in Cromwell's time was as marshy as the fens of Lincolnshire, we cannot feel surprise at the extraordinary mortality from ague. See MARSHES, FEVERS, MALARIAS, &c. Air-It was long thought that air was an element, a kind of ether, but we now know that it is just as material as a bit of iron or lead; and the time may yet come when, by the aid of immense pressure and intense cold, the air may be condensed into a liquid. As yet it has, however, never been made visible, like carbonic acid gas, nitrous oxide, and some other gases. It is transparent, inodorous, and without colour. A cubic foot, at 60° F. and 30° Bar., weighs 536 96 grains; a litre, at the same temperature and pressure, weighs 1-299100 grammes. Its average composition in England is as follows: Before entering upon a description of each of these constituents, it will be well to consider a few of the properties of air, one of the most important of which is its power of penetration, and its universality. Air is indeed present everywhere; there is scarcely a solid, however compact it may appear to be, which does not contain pores, and these pores filled with air. The soil contains no small quantity; indeed, if it were not so, the numberless insects, worms, &c., which burrow in its interstices would cease to exist. The most compact mortar and walls are penetrated with it, and water of natural origin contains a large quantity of air in solution. The atmosphere is supposed to extend to a very great height, from 200 to 300 miles; it used to be considered only five miles high, but observations on shooting-stars, &c., show that this opinion is erroneous. Owing to the force of gravity, the air is much denser near the earth, and gets more attenuated, layer by layer, as you ascend. If, then, the atmosphere were possessed of colour, it would be very dark just round the globe, and the tint would gradually fade into space. The air is by no means wholly gaseous; it contains, indeed, an immense amount of life, and small particles derived from the whole creation. In the air may be found ani malcules, spores, seeds, pollen, cells of all kinds, vibriones, elements of contagia, eggs of insects, &c., and a few fungi, besides formless dust, sandy and other particles of local origin; for example, no one can ride in a railway carriage without being accompanied with dust, a great portion of which is attracted by a magnet, and is, indeed, minute particles of iron derived from the rails. The purest air has some dust in it. There probably never fell a beam of light from the sun since the world was made which did not show, were there eyes to see it, myriads of motes; these, however, generally speaking, are quite innocuous to man (see DUST)—some, indeed, may possibly be beneficial. Another most important property of air is its mobility; on the calmest day, and in the quietest room, there are constant currents of air which rapidly dilute any noxious odours or gases. Oxygen. The uniformity of the actual amount of oxygen in the air of different places is remarkable. Normal air contains 20.96 of oxygen in 100 parts, and any differences that may exist in various ocalities are almost always, when analysed by accurate chemists, to be found in the second decimal place. For example, Regnault analysed the following specimens: In towns the carbonic acid varies, but is from 20-913 to 20-999 generally higher than in open places. 9 20.918 20.966 20.908 20.998 20.916,, 20.982 Per cent. The mean of 14 analyses, by Angus Smith, in Manchester (suburbs) -0369 About middens, of which there are thousands Nitrogen. This gas is one of the most in. different of the elements; while oxygen, to which it is united, is one of the most energetic. It is generally considered to be a mere dilutant of the oxygen, and to serve the purpose of moderating its action both on combustion and life. The average amount of nitrogen is 79.00 per 100 in normal air. Carbonic Acid (see ACID, CARBONIC).—This gas, theoretically speaking, is not a constituent of normal air, but the actual fact is that it nearly always exists in minute proportions even in the best air; and if we think of the sources of this gas, the reason of its presence is obvious. The processes of respiration, combustion, and decay of vegetable and other organic matter, besides other less obvious and less constant sources, are continually, though silently, evolving it. The following examples from the lungs and skin. In fact, a consider- | of excessive contamination by gases, dust, and able quantity of carbonic acid gas is breathed smoke. Dr. Angus Smith made 339 analyses by workers in certain manufactories, e.g., of the air of mines. Of these, 38 had the soda-water, &c., without injury, although in normal amount of oxygen. The mean of the large quantities, and undiluted, it is rapidly 38 normal specimens was 20'94 oxygen. The fatal; while comparatively speaking small mean of 31 normal specimens in which the quantities in theatres, assembly-rooms, and carbonic acid was estimated was 083. The other places, where human beings are crowded mean of the whole 393 specimens was 20-26 together, have a very depressing effect, be- per cent. oxygen; carbonic acid, 785. The cause there are other impurities in the air. highest oxygen found was 21'04 per cent.; the Ozone. This is generally considered to be lowest was 18:27 per cent. The least caran allotropic form of oxygen. Three atoms of bonic acid found was 02 per cent.; the oxygen are condensed into one molecule, as greatest number for carbonic acid was 2.73 per is represented by the formula 03. It exists cent. The analyses were divided into three in variable quantity in the air, and probably groups-those that showed the air normal, or is of some importance. For full details and nearly so; those that were decidedly impure; tests, see OZONE. and those that were exceedingly impure : The Air of Towns has generally traces of sulphuric, hydrochloric, sulphuretted, and other acids, derived from combustion and different manufactories, besides a considerable quantity of suspended particles of carbon-dust, derived from traffic and emanations from human beings. The air, even of small towns, has more organic matter than country-places (see RAIN-WATER, ANALYSIS OF), which is easily shown by estimating the ammonia and albuminoid ammonia in air. The carbonic acid is of course increased. The oxygen is decreased, but only to a small amount. For example, the mean of the 22 analyses by Dr. A. Smith of the worst places in Perth gave 20.938; while on the sea shore and the heath the mean of several analyses gave 20-999. Odorous particles of all kinds are more common in towns. The Air of the Country and Open Places varies a little, according to elevation, vegetation, whether populated or not, &c. But the general result is that the oxygen is greater, and the carbonic acid less, than in towns, while the air is free from the acid emanations and carbon so copiously poured out from towns. Of all places, heaths and mountains, as would be expected, possess the best and purest air. Dr. Angus Smith's analysis of mountainous districts in Scotland gave a mean of 20.94 oxygen, while the carbonic acid of the same mountains, taken, however, at a different time, gave 0331. Dr. Pietra-Santa observes that the air of hills or mountains, at the height of 2300 feet, is lighter than common air, contains in equal volume a smaller proportion of oxygen, and is impregnated with a more considerable amount of aqueous vapour; it also contains a good deal of ozone. He considers such a climate peculiarly soothing to persons suffering from certain maladies, such as chest diseases, &c. The Air of Mines.-The greatest variety of atmosphere occurs in mines, the quality of the air ranging from that of fair purity to that which is equal to % of the volume of air passing through the lungs. It will be readily understood, after these figures, the importance of pure air, and how minute differences in composition are really of great importance, since the lungs act, as it were, as immense strainers or filters, and catch the floating particles, while they rapidly absorb deleterious gases. The amount of air required by each person in a room is no less than 2100 feet per hour. When the ventilation does not allow of this constant change, it smells stuffy, the furniture becomes coated with a film of organic matter unless constantly cleaned, and the carbonic acid becomes increased to more than its normal amount. The effect of constantly breathing impure air necessarily varies as to its state of pollu tion and other circumstances. When the impurity is moderate, the first effect is headache, lassitude, and a general paleness of the face and skin, owing to a diminution of the red globules of the blood. If the food is insufficient, other evils, such as scrofula and consumption, are very common. For instance, Dr. Guy showed the great mortality from consumption in those trades in which workmen pursued their calling in hot, close, gas-lit rooms, in comparison to those who passed most of their time in the open air. If the air is vitiated to a large extent, it is quickly fatal, not alone probably from the carbonic acid exhaled, but from the exhalation from the skin and lungs. In the Black Hole of Calcutta, as well as in the case of the Austrian prison after the battle of Austerlitz, d de Fig. 2. where 260 out of 300 prisoners died rapidly, the symptoms were rather those of bloodpoisoning than anything else. There was great fever, restlessness, and eruptions and boils appeared among the survivors. The effect of impure air is not alone seen on man, but also on animals. Cows, horses, and sheep, if penned up in close stables or outhouses, show a great mortality from phthisis and other diseases. The effect of dust in air, affecting the workmen employed in various arts, will be considered under DUST. ties in the air to the ground as it descends. See RAIN. The ordinary analysis of air embraces the estimation of the following constituents: oxygen, nitrogen, carbonic acid, aqueous vapour, and ammonia. Aqueous Vapour, Determination of. -To determine the water, an aspirator must be used. They are easily made, and not expensive. The above is a diagram of the arrangement generally adopted (fig. 2). a is an aspirator made of galvanised iron or sheet zinc. It holds from 50 to 100 litres. A known Analysis of the Air.-For health purposes volume of air by this means is drawn through much information may be obtained on the the tubes marked b, c, d, e, which may be composition of the air from chemical examina- filled with pumice stone, moistened with tion of the rainfall of the different parts of a strong sulphuric acid; but if the carbonic district, for the rain washes down the impuri-acid is to be estimated as well, b and c are filled with moist hydrate of lime (potash used acid. A portion of this baryta-water is then to be employed, but hydrate of lime is to be pre-made to act upon a definite quantity of air. It ferred, as the potash absorbs oxygen as well), will absorb the whole of the carbonic acid in and d and e as above. Each of the tubes is ac- that air. In consequence, the alkalinity of the curately weighed previous to connecting them liquid will be diminished; it will take less of with the apparatus. It is obvious that each the oxalic acid solution than before, which of the tubes must be connected by perfectly shows so much less caustic baryta, and from air-tight joints. They are usually coated with which the carbonic acid absorbed may be easily sealing-wax. The gain of weight in d, e gives calculated. the water, in b and c, the carbonic acid. Carbonic Acid.-For the exact determination of the carbonic acid the following method, known as Pettenkofer's, is better. It may be shortly defined as follows: Baryta-water of definite strength is prepared and accurately standardised by a standard solution of oxalic The Actual Analysis.-Two kinds of barytawater may be used, the one containing 7 grm. to the litre, the other three times that strength. 1 c.c. of the stronger 3 mgrms. of carbonic acid, 1 c.c. of the weaker, 1 mgrm. The barytawater is best kept in the bottle represented in fig. 3. = The bottle a contains the baryta-water. It has an accurately-fitting double-perforated caoutchouc stopper. The left-hand tube is connected with tube b, containing pumicestone, moistened with potash, while the righthand one is a siphon. When required for use, the stopcook ƒ is opened, and suction applied by a glass tube to F. The siphon is thus filled, and the stopcock closed. If a pipette is required to be filled, its nozzle is inserted at F, the stopcock compressed, and the fluid immediately rises into the pipette. The air entering the bottle as the fluid decreases in a is of course thoroughly deprived of its carbonic acid by the tubes at b. The first thing to be done is to standardise the baryta solution by a solution of oxalic acid, containing 2.8636 grammes of crystallised oxalic acid to the litre. (See ACID, OXALIC.) Thirty c.c. of baryta solution are run into a small flask, and the oxalic acid run in from a Mohr's burette with float, the vanishing-point of the alkaline reaction being ascertained by delicate turmeric paper. As soon as a drop placed on turmeric paper does not give a brown ring the end is attained. The actual analysis is performed by filling a bottle of known capacity, with the aid of a pair of bellows, with the air to be analysed, then distributing over its sides 45 c.c. of the |