Acid rain

“ Our tour ends here, but there are many more stone buildings and monuments in Washington and in other cities that may also show the effects of urban pollution and acid precipitation. However, as seen on this tour, not all of the deterioration of stone buildings is caused by acid rain. To protect our historic stone buildings and monuments, we need to limit air pollution that contributes to acid rain deterioration, and we need to develop effective maintenance and preservation procedures that will not further harm the stone. ”

“ In addition, the process of weathering has been going on since the Earth first had an atmosphere. Although we can observe deterioration of the stone, it is hard to determine how much of the deterioration is from acid precipitation and how much is from other causes. ”

“ The rain-water that descends upon the land holds in solution carbonic acid which it has absorbed from the air. But water charged with carbonic acid is capable of dissolving carbonate of lime, and thus year after year the rains slowly remove as they sink to the drains, or run over the surface, a portion of the lime which the soil contains. Acid substances are also formed naturally in the land, by which another portion of the lime is rendered easily soluble in water, and, therefore, readily removable by every shower that falls. ”

“ The rock suffers, however, from its solubility in water containing even a mild acid. In the gases dissolved by rain-water from the atmosphere, carbon dioxide assumes a far larger proportion than that which it possesses in the air itself. The surface of limestone slabs becomes in consequence pitted and corroded by every rain that falls. The sulphuric acid in the air of modern coal-consuming cities is, however, still more deadly in its action. ”

“ There is a beautiful adjustment in the constitution of the atmosphere to the nature and necessities of living beings. The energy of the pure oxygen is tempered, yet not too much weakened, by the admixture of nitrogen. The carbonic acid, which alone is noxious to life, is mixed in so minute a proportion as to be harmless to animals, while it is still beneficial to plants; and when the air is overloaded with watery vapour, it is provided that it shall descend in rain. ”

“ Gerald Moody, during the last few years, that if there were no acid gas present, the rusting would not take place. Oxygen and carbonic acid will rust other things beside metal; they will rust stone. Moreover, when the rain reaches the earth it absorbs any other acids of the soil which rotting vegetation may afford, and reinforced by these it goes on to attack the stones over which it flows. When it rolls along as a brook or a river it is no doubt attacking in this way the rocks -48- and stones of its channel, though this action is not very strikingly shown. ”

“ Rain water, when collected in the country, is doubtless the purest and best adapted for ordinary household purposes, but in London and large cities it contains many impurities; when collected in our tubs or cisterns, it is impregnated with all the dust, dirt, and smoke that hangs more or less like a funeral pall over smoky cities; the air contains more or less sulphurous acid, and the carbon that escapes from our chimneys and is deposited on the tops of our houses, hence the sooty taste that soft or rain water has. ”

“ Of the other constituents of the atmosphere, the combined forms of nitrogen—viz., ammonia, nitric, and nitrous acids—are the most important. These are all absorbed by the soil, but, like carbonic acid, they are chiefly washed down by the rain. The amount of ammonia which may be absorbed by a soil from the air, is very much greater than was formerly supposed. Some recent experiments by Schloesing, referred to in a following chapter, [48] show this. A damp soil may in the course of a year absorb far more ammonia than that washed down in rain. ”

“ Spots of acid on clothing fall too often under the observation of all those engaged in practical chemical work. However quickly a spot of acid is wiped off, unless it is immediately neutralised by ammonia, it ultimately makes a hole in the cloth; the spot, as a rule, whatever the colour of the cloth, is of a blotting-paper red.
Sulphuric acid dropped on iron, attacks it, forming a sulphate, which may be dissolved out by water. If the iron is exposed to the weather [81] the rain may wash away all traces of the acid, save the corrosion ”

“ Rain always absorbs a little air, which, in addition to its nitrogen and oxygen, contains carbonic acid, and in minute proportions, sodium chloride, sulphuric acid and other ingredients, especially inorganic dust, organic particles and living germs. Probably the most generally efficient of these constituents are oxygen, carbonic acid and organic matter. Armed with these reagents, rain effects a chemical decomposition of the rocks on which it falls, and through which it sinks underground. ”

“ A great number of bodies which arise from industrial processes, domestic combustion of coal, natural changes in vegetable and animal matter, terrestrial disturbances as tornadoes and volcanic eruptions, vital exhalations, etc., are discharged into the atmosphere, and, whether by solution or mechanical contact, descend to the surface of the earth in the rain, leaving upon its evaporation in many instances the most incontestable evidences of their presence. The acid precipitation around alkali and sulphuric acid works is well known ”

“ After a period of several weeks of fair weather during the summer, rain fell, and the sample of water running from a roof was caught and evaporated; the residue when dried weighed 1.68 grammes. It was of a brownish black color, fusible in heat and readily soluble, with a yellow brown color in water. The dark brown substance readily dissolved in ammonia, alcohol, dilute acid, hydrochloric acid, sulphuric acid, and decomposed in nitric acid, but did not dissolve in benzine or fat oil. ”

“ In specific gravity, it scarcely differs from distilled water. It nevertheless generally holds in solution common air, carbonic acid, carbonate of132 lime, chloride of lime, and a trace of nitric acid. If it be collected from the roofs of houses, after it has rained for some time, it contains sulphate of lime and occasionally carbonate of lead. The quantity of common air in rain water does not exceed 31⁄2 cubic inches in 100 cubic inches of water; it contains more oxygen than atmospherical air; the same quantity of rain water contains one inch of carbonic acid gas. ”

“ On the surface of the plain there has always been growing abun [Pg 185] dant vegetation, the remains of which decayed on the surface in the manner which we may observe at the present day. This decomposing vegetable matter within and upon the porous alluvial material produces large quantities of carbonic acid, a gas which readily enters the rain water, and gives it a peculiar power of breaking up rock matter. Acting on the débris, this gas-charged water rapidly brings about a decay of the fragments. ”

“ As all the saline components of the ocean are nonvolatile, rain water, in its natural state, can be contaminated only with the ordinary atmospheric gases—oxygen, nitrogen and carbon dioxide. Rain water also contains perceptible traces of ammonia, combined as a rule, at least partly, with the nitric acid, which is produced wherever an electric discharge pervades the atmosphere. ”

“ The moisture contained in the bed is primarily rain water, and it is not easy to see what active agent it can become charged with in draining into the interior of the mass, except carbonic acid or carbonate of lime: any of the stronger acids, such as the sulphuric, resulting from the decomposition of pyrites, would immediately be neutralized by the calcareous matter in which the whole bed abounds. Alternations of moisture and dryness, of heat and cold, to which the decomposition of the exposed surfaces of rocks is so generally attributed, could have little or no influence in this case ”

“ It proposes to send up liquefied carbonic acid and to set it free in the portion of air from which it is desired to precipitate the rain. The carbonic acid in vaporizing and expanding must take heat from the surrounding air sufficient to set its molecules vibrating in the gaseous form. Unquestionably we have here the proper kind of an agent for producing rain. The only question to be considered is one of finance. ”

“ The rain falling through the air carries with it a certain amount of carbonic acid and ammonia, which the air always contains, and it is the whole source of the nitrogen which forms a very important part of the bodies of plants and animals. When the rain arrives at the surface of the earth, it sinks down into it and carries with it all soluble vegetable or animal matter which it meets with, together with any soluble earthy matter which may exist in the soil ”

“ The air freest from impurities is that collected at the sea-coast and at considerable heights. Again, ammonia is found to diminish, while nitric acid increases, in ascending to, at least, habitable heights. As regards organic matter in the air, it corresponds to a con siderable extent with the density of the population. As might have been supposed from the higher temperature, more nitric acid is contained in rain collected on the Continent than in the British Islands. ”

“ The injurious effects of acids on vegetation are indicated chiefly by the shrivelled-up appearance which the leaves of herbage, trees, &c., exhibit in the vicinity of chemical works in which the condensation of noxious gases (hydrochloric acid, sulphurous acid, sulphuric acid, sulphuretted hydrogen, nitric acid, and oxides of nitrogen and chlorine) is not effectually carried out. ”

“ In warm weather it will even keep smoking many days without the application of any other heat.
On this account, it should be placed where there are no instruments, or any thing of metal, that can be corroded by this acid vapour. It is from dear-bought experience that I give this advice. It may easily be perceived when this phial is throwing out this acid vapour, as it always appears, in the open air, in the form of a light cloud; owing, I suppose, to the acid attracting to itself, and uniting with, the moisture that is in the common atmosphere. ”

“ The Common Gases dissolved or imprisoned by well and spring water are carbonic acid, sulpurretted hydrogen and the components of air—oxygen and nitrogen. Of these only one is dangerous—sulpurretted hydrogen—and that is easily detected by its smell, resembling that of spoiled eggs. It gives the characteristic odor to “sulphur” waters. Carbonic acid and air give to waters their sparkling quality—the former being often artificially introduced, as in “soda-water,” &c.
The Organic Matter in well, spring, and river water may be dead or living, and we will consider the two classes separately. ”

“ It is purest when it runs over a gravelly or rocky bed, and when its course is swift. It is generally soft, and more free from earthy salts than spring water; but it usually contains less common air and carbonic acid gas; for, by the agitation of a long current, and exposed to the temperature of the atmosphere, part of its carbonic acid gas is disengaged, and the lime held in solution by it is in part precipitated, the loss of which contributes to the softness of the water. ”

“ The people attached to the embassy told us that when there is any wind, the vapours are scarcely perceptible, but that they are very dangerous when the weather is calm and serene. Carbonic acid gas being, as the reader is aware, heavier than the atmospheric air, necessarily condenses on the surface of the ground, and remains fixed there until some great agitation of the air sets it in movement, disperses it in the atmosphere, and neutralizes its effects. ”

“ When the body of a man, or of an animal, is exposed to the combined influences of air, of water, and of a moderately high temperature, it undergoes a series of chemical decompositions, whose final term is its transformation into carbonic acid gas, and some compounds, gaseous or solid, which represent the less advanced products of destruction. Gases of various kinds, carbonic acid, hydrosulphuric, and ammoniac, and the vapour of water, spread themselves through the atmosphere, or dissolve into the humidity of the soil. ”

“ This is not boiling, as may be proved by trying the temperature with the finger. What, then, is it?
It is the yielding back of the atmospheric gases which the water has dissolved or condensed within itself. These bubbles have been collected and by analysis proved to consist of oxygen, nitrogen, and carbonic acid, obtained from the air; but in the water they exist by no means in the same proportions as originally in the air, nor in constant proportions in different samples of water. ”

“ These two gases are mixed in nearly the same proportions in all climates so as to make the beautiful pure air which God has given us to live and go about in. There is another gas, called carbonic acid, made partly of oxygen and partly of carbon, or burnt wood, which might be called "life-destroyer," for it will put out light and make an end of life. It is one of the most deadly poisons, and forms the "choke-damp" which too often suffocates the miner; but what we call fresh air contains such a very small proportion of this dangerous gas that it is harmless. ”

“ Occasionally offensive effluvia arise in connection with industries in which neither vegetable nor animal matters are used; as in the manufacture of sulphate or chloride of ammonia, and some other processes in which sulphuretted hydrogen is copiously evolved; and in the making of gas and the distillation of tar. The fumes from the manufacture of alkali and bleaching powder are acid and irritating, and produce very injurious effects on vegetation in the neighbourhood. ”