The Atlantic Monthly, Volume 09, No. 55, May, 1862

And polar frost my frame defied,
Made of the air that blows outside."

With glad remembrance of my debt,
I homeward turn. Farewell, my pet!
When here again thy pilgrim comes,
He shall bring store of seeds and crumbs.
Henceforth I prize thy wiry chant
O'er all that mass and minster vaunt:
For men mishear thy call in spring,
As 'twould accost some frivolous wing,
Crying out of the hazel copse, "Phe—be!"
And in winter, "Chic-a-dee-dee!"
I think old Caesar must have heard
In Northern Gaul my dauntless bird,
And, echoed in some frosty wold,
Borrowed thy battle-numbers bold.
And I shall write our annals new,

And thank thee for a better clew:
I, who dreamed not, when I came here,
To find the antidote of fear,
Now hear thee say in Roman key,
"Paean! Ve-ni, Vi-di, Vi-ci."

* * * * *

SALTPETRE AS A SOURCE OF POWER

Every element of strength in a civilized community demands special notice. The present material progress of nations brings us every day in contact with the application of power under various conditions, and the most thoughtless person is to some extent influenced mentally by the improvements, taking the places of older means and ways of adaptation, in the arts of life.

We travel by the aid of steam-power, and we think and speak of a locomotive or a steamboat as we once thought and spoke of a horse or a man; and no little feeling of self-sufficiency is engendered by the conclusion that this new source of power has been brought under control and put to work in our day.

It is also true that we do not always entertain the most correct view of what we term the new power of locomotive and steamboat; and as it may aid us in some further steps connected with the subject of my remarks, a familiar object, such as a steamboat, may be taken as illustrative of the application of power, and we may thus obtain some simple ideas of what power truly is, in Nature.

My travelled friend considers a steamboat as a ship propelled by wheels, the shaft to which they are attached being moved by the machinery. He follows back to the piston of the engine and finds the motor there,—satisfied that he has discovered in the transference of rectilinear to rotatory motion the reason for the progress of the boat. A more inquisitive friend does not rest here, but assumes that the power of the steam flowing through the machine sets in action its parts; and he rests from farther pursuit of the power, where the larger number of those who give any observation to the application of steam are found,—gratified with the knowledge accumulated, and the readiness with which an explanation of the motion of the boat can be traced to the power of steam as its source.

We must proceed a little farther on our backward course from the point where the power is applied, and in our analysis consider the steam as only the vehicle or carrier of the power; and examining the conditions, we find that water acted on by fire, while contained in a suitable vessel, after some time takes up certain properties which enable it to go forward and move the ponderous machinery of the boat. The water evidently here derives its new character of steam from the fire, and we have now reached the source of the movement of steam, and traced it to the fire. In fact, we have found the source of power, in this most mechanical of all mechanical machines, to be removed from the department of knowledge which treats of machines!

But we need not pause here, although we must now enter a little way into chemical, instead of mechanical science. The fire prepares the water to act as a carrier of power; it must contain power, therefore; and what is it which we call fire? In placing on the grate coal or wood, and providing for the contact of a continuous current of air, we intend to bring about certain chemical actions as consequent on a disposition which we know coal and wood to possess. When we apply fire, the chemical actions commence and the usual effects follow. Now, if we for a moment dismiss the consideration of the means adopted, it becomes apparent to every one, that, as the fire will continue to increase with successive additions of fuel, or as it will continue indefinitely with a regular supply, there must be something else than mere motor action here. We cannot call it chemical action, and dismiss the thought, and neglect further inquiry, unless we would place ourselves with those who regard the movement of the steamboat as being due to the machinery.

Our farther progress in this analysis will soon open a wide field of knowledge and inquiry; but it is sufficient for our present purpose, if, by a careful study of the composition and chemical disposition of the proximate compounds of the coal and the wood fuel, we arrive at the conclusion that both are the result of forces which, very slight in themselves at any moment, yet when acting through long periods of time become laid up in the form of coal and wood. All that effort which the tree has exhibited during its growth from the germ of the seed to its state of maturity, when taken as fuel, is pent up in its substance, ready, when fire is applied, to escape slowly and continuously. In the case of the coal, after the growth of the plant from which it was formed, the material underwent changes which enabled it to conserve more forces, and to exhibit more energy when fire is applied to its mass; and hence the distinction between wood and coal.

Our analysis thus far has developed the source of the power moving the steamboat as existing in the gradual action of forces influencing vegetation, concentrated and locked up in the fuel. For the purpose of illustrating the subject of this essay, we require no farther progress in this direction. A moment of thought at this point and we shall cease to consider steam-power as new; for, long before man appeared on this earth, the vegetation was collecting and condensing those ordinary natural powers which we find in fuel. In our time, too, the rains and dews, heat, motion, and gaseous food, are being stored up in a wondrous manner, to serve as elements of power which may be used and applied now or hereafter.

In this view, too, we may include the winds, the falling of rain, the ascent and descent of sap, the condensation of gases,—in short, the natural powers, exerted before,—as the cause of motion in the steamboat.

Passing from these considerations not unconnected with the subject, let us inquire what saltpetre is, and how it is formed.

The term Saltpetre is applied to a variety of bodies, distinguished, however, by their bases, as potash saltpetre, soda saltpetre, lime saltpetre, etc., which occur naturally. They are all compounds of nitric acid and bases, or the gases nitrogen and oxygen united to bases, and are found in all soils which have not been recently washed by rains, and which are protected from excessive moisture.

The decomposition of animal and of some vegetable bodies in the soil causes the production of one constituent of saltpetre, while the earth and the animal remains supply the other. Evaporation of pure water from the surface of the earth causes the moisture which rises from below to bring to the surface the salt dissolved in it; and as this salt is not volatile, the escape of the moisture leaves it at or near the surface. Hence, under buildings, especially habitations of men and animals, the salt accumulates, and in times of scarcity it may be collected. In all cases of its extraction from the earth several kinds of saltpetre are obtained, and the usual course is to decompose these by the addition of salts of potash, so as to form from them potash saltpetre, the kind most generally consumed.

In this decomposition of animal remains and the formation of saltpetre the air performs an important part, and the changes it effects are worthy of our attention.

Let us consider the aërial ocean surrounding our earth and resting upon it, greatly larger in mass and extent than the more familiar aqueous ocean below it, and more closely and momentarily affecting our well-being.

The pure air, consisting of 20.96 volumes of oxygen gas and 79.04 volumes of nitrogen gas, preserves, under all the variations of climate and height above the surface of the earth, a remarkable constancy of composition,—the variation of one one-hundredth part never having been observed. But additions and subtractions are being constantly made, and the atmosphere, as distinguished from the pure air, is mixed with exhalations from countless sources on the land and the sea. Wherever man moves, his fire, his food, the materials of his dwellings, the soil he disturbs, all add their volatile parts to the atmosphere. Vegetation, death, and decay pour into it copiously substances foreign to the composition of pure air. The combustion of one ton of coal adds at least sixteen tons of impurity to the atmosphere; and when we estimate on the daily consumption of coal the addition from this source alone, the amount becomes enormous.

Experiments have been made for the purpose of estimating these additions, and the results of those most carefully conducted show how very slightly the combined causes affect the general composition of our atmosphere; and although the present refined methods of chemists enable them to detect the presence of an abnormal amount of some substances, no research has yet been successful in determining how far this varies from the natural quantity at all times necessarily present in the atmosphere.

It is, however, the comparatively minute portions of nitrogenous matter in the atmosphere that we are to consider as the source of the nitrous acids formed there, and of part of that found in the earth. From some experiments made during the day and night it has been found, that, under the most favorable circumstances, six millions six hundred and seventy thousand parts of air afford one part of nitrogenous bodies, if the whole quantity be abstracted! A portion only of this quantity can be withdrawn in natural operations, such as the falling of rain and the deposition of dew,—the larger part always remaining behind.

When the oxygen of our atmosphere is exposed, while in its usual hygrometric state, to the influence of bodies attracting a portion of it, such as decomposing substances, or when it forms the medium of electrical discharges, it suddenly assumes new powers, acquires a greatly increased activity, affects our organs of smell, dissolves in fluids, and has been mistaken for a new substance, and even named "ozone." Among the new characters thus conferred on it is the power of uniting with or burning many substances. This ozonized oxygen, when brought into mixture with many nitrogenized bodies, forms with them nitrous acids, completely destroying their former condition and composition; hence, in the atmosphere, this part of the oxygen becomes a purifier of the whole mass, from which it removes putrescent exhalations, miasmatic vapors, and the effluvia from every source of sea or land. Very curious are the effects of this active oxygen, which is ever present in some portion of the atmosphere. Moved by the wind, mixed with the impure upward currents rising from cities, it seizes on and changes rapidly all foulness, and if the currents are not too voluminous, the impure air becomes changed to pure. As ozonized oxygen can be easily detected, we may pass from the city, where (overpowered by the exhalations) it does not exist, and find it in the air of the vicinity; and moving away several miles, ascertain that a normal amount there prevails, and that step by step, on our return to abodes of a dense population, the quantity diminishes and finally all disappears.

We are now prepared to answer the second part of the question which was suggested, and to find that nitrous acids formed in the atmosphere by direct oxidation of nitrogenous matter may unite with the ammonia present to produce one kind of saltpetre; and when the rains or the dews carry this to the earth, the salts of lime, potash, and soda there found will decompose this ammoniacal saltpetre, and set the ammonia free, to act over again its part. So in regard to decomposing organic matters in the soil: ozonized oxygen changes them in the same way. The earth and calcareous rocks of caves, penetrated by the air, slowly produce saltpetre, and before the theory of the action was understood, artificial imitation of natural conditions enabled us to manufacture saltpetre. Animal remains, stratified with porous earth or the sweepings of cities, and disposed in long heaps or walls, protected from rain, but exposed to the prevailing winds, soon form nitrous salts, and a large space covered with these deposits carefully tended forms a saltpetre plantation. France, Prussia, Sweden, Switzerland, and other countries, have been supplied with saltpetre from similar artificial arrangements.

But the atmosphere is washed most thoroughly by the rains falling in and near tropical countries, and the changes there are most rapid, so that the production of saltpetre, favored by moisture and hot winds, attains its highest limit in parts of India and the bordering countries.

During the prevalence of dry winds, the earth in many districts of India becomes frosted over with nitrous efflorescences, and the great quantity shipped from the commercial ports, and that consumed in China, is thus a natural production of that region. The increased amount due to tropical influences will be seen in the instances here given of the produce from the rich earths of different countries:—

Natural.

France, Church of Mousseau, 5-3/8 per cent.

" Cavern of Fouquières, 3-1/2 "

U. States, Tennessee, dirt of caves, 0.86 "

Ceylon, Cave of Memoora, 3-1/10 "

Upper Bengal, Tirhoot, earth simply, 1-6/10 "

Patree in Guzerat, best sweepings, 8-7/10 "

In each case the salt is mixed saltpetres.

Artificial.

France, 100 lbs. earth from

plantations afford 8 to 9 oz.

Hungary and Sweden, from

the same, 1/2 to 2-3/10 per cent.

It may be calculated that the flesh of animals, free from bone, carefully decomposed, will afford ninety-five pounds of saltpetre for one thousand pounds thus consumed.

In the manufacture of saltpetre, the earths, whether naturally or artificially impregnated, are mixed with the ashes from burnt wood, or salts of potash, so that this base may take the place of all others, and produce long prisms of potash saltpetre.