CHAPTER XIV.

Air of Inhabited Districts, of the Country, of the Sea-coast, and of the Ocean-Quantity of Carbon in the Air of a London Music Hall-Quantity of Carbon in the Earth's Atmosphere -Quantity of Carbon in Organized Beings-The New Gas Argon" Forest Air The Author's Observations in Waldeck, etc.-The Influence of Trees on the Air of Towns -Influence of Forests on Rainfall known to Columbus--The Author's Explanation based on direct Observation.

THE term Atmosphere should, properly, be applied only to the gaseous envelope of the Earth; whilst the term air is used to denote a limited portion of the atmosphere, such as the lower portion in which we live, the air of rooms, of mines, of forests, the air of the sea, etc.

Ordinary air, in inhabited districts, yields to analysis, in round numbers, 21 volumes of oxygen and 79 of nitrogen; it contains, on an average, 4 volumes of carbonic acid in 10,000 volumes of air, and in the open country this amount will fall as low as 3 parts in 10,000, whilst over the ocean, according to Beauvais, there is a mere trace of this gas in the air, a fact, doubtless, to be accounted for by the solubility of carbonic acid in water.

My late distinguished friend, Dr. Verhaeghe, of

Ostend (Belgium), found only 21⁄2 parts of carbonic acid in 100,000 volumes of air on the coast, which is more than 10 times less than is found in inland districts.

As carbonic acid is known to be very deleterious to consumptive patients, its almost complete absence over the waters of the ocean is one of the reasons that has caused physicians to recommend sea-voyages for sufferers of this kind.

Although the relative amount of carbonic acid in the air appears, at first sight, to be exceedingly small, its absolute amount in the whole atmosphere is exceedingly great. Let us take the average contents of the atmosphere in carbonic acid at 4 parts in 10,000. A room 25 feet long, 25 feet broad, and 16 feet high, would hold 10,000 cubic feet of air, with its 4 cubic feet of carbonic acid; and these 4 cubic feet of this gas would weigh 2455 grains and contain 607 grains of carbon (equal to a piece of charcoal about the size of a hen's egg).

A large music hall in London contains about 150,000 cubic feet of air, and consequently, the amount of carbonic acid contained in it will be 15 times 4, or 60 cubic feet, and the amount of carbon 15 times 607 grains, or more than 1 lbs.

When we pass from the consideration of the air, in rooms, large or small, to that of the Earth's atmosphere in its present condition, we get results almost beyond conception :

The weight of the air overlying every square inch of the Earth's surface is in round numbers about 15 lbs.,

or 2160 lbs. on the square foot. So that every square foot of the Earth's surface has overlying it 2160 lbs. of air; and this quantity of air contains about 11⁄2 lbs. of carbonic acid, equivalent to nearly lb. of carbon.

The organized beings on the Earth's surface contain on an average 45 per cent. of carbon (nearly half their weight), and from a single acre of wheat land, some 2000 lbs. of carbon are taken in a single season. Now, if we reckon from acres to feet, we find that, during the whole period of its growth, this crop of wheat, which yields 2000 lbs. of carbon, has overlying it some 20,000 lbs. of carbon in the form of atmospheric carbonic acid, which is infinitely in excess of the wants of vegetation in this respect; and the quantity of carbon in the entire atmosphere, as carbonic acid, is far in excess of that contained in all living beings, both plants and animals, existing on the surface of the Earth, and in the inflammable carbonaceous minerals, such as coal, lignite, peat, etc., which lie buried beneath its surface, as far as we can estimate this quantity with any degree of probability.

The supposed new gas in the atmosphere, which has recently been brought before the public by Lord Rayleigh and Professor Ramsay, who have given to it the name of "Argon" (inert) on account of its absolutely inert properties, and which, they say, forms. about 1 per cent. of atmospheric air, appears to several chemists to be an allotropic form of nitrogen, similar to what ozone is to oxygen; or a protocarbide of nitrogen. It remains as a residue when a mixture of oxygen and

nitrogen is submitted to a long series of electric sparks, until no more nitric acid can be formed in this way. This inert residue was observed by Cavendish, who first made this experiment, in the last century It weighs rather more than ordinary nitrogen, just as ozone is denser than oxygen. It is not absorbed by red-hot magnesium, as ordinary nitrogen is; and the figures given in the author's paper, read to the Royal Society, point to the probability of its being 3 molecules of nitrogen condensed into 2 molecules, similar to what the late Dr. Andrews of Belfast found to be the case with ozone, as regards oxygen. Lord Rayleigh had noticed that the nitrogen gas obtained from ammonia, or from nitric acid, weighed slightly less than the nitrogen obtained from the atmosphere, and this caused him to believe that the atmosphere contained some unknown constituent which increased the height of its nitrogen. This led to a series of very laborious researches, in which he was assisted by Professor Ramsay, and ended in the discovery of the gaseous substance they call "argon."

When oxygen takes the allotropic form of ozone, its characteristic properties are enhanced, its tendency to combine with other bodies is much greater, its activity is wonderfully increased.

when it passes into the state of argon, its inert nature
becomes even more apparent than it usually
In the case of nitrogen,

is exactly what we should expect 1

1 See Phipson,

Comptes-ren

CARBONIC ACID-OZONE-FORESTS.

93

theless, prove to be a carbide of nitrogen containing half as much carbon as cyanogen, which would have the same density.

The beneficial influence of forest air has often been ascribed to a large amount of oxygen, less carbonic acid, and the presence of balsamic, aromatic vapours. But analysis shows that there is very little, if any, extra oxygen during the day, and rather more carbonic acid at night, than in the open air of the country.

The wind constantly tends to mix the forest air with that of the fields and plains, and the hygienic influence of the former must be ascribed in great measure to its freedom from dust and disease germs. It is, so to say, filtered air.

The diurnal variations of temperature are also slighter in forests than in the open country. Woods are usually warmer than the adjacent atmosphere. I have noticed that the forests on the hills of Waldeck, in Germany, appear to smoke, after heavy rain in June, an effect due to the moisture rising with the warm air of the woods into the cooler atmosphere above them. I have seen the same effect on a garden wall in London, which being heated by the summer sun for some hours, emitted steam after a heavy shower of rain.

Once in a hot crowded room in Paris, I witnessed a similar condensation of invisible moisture into visible steam, from a reverse process. It occurred over plates of ice handed to the guests: each ice appeared to smoke, like a miniature volcano, producing a most singular effect.