1. The atmosphere consists of particles of two kinds of gases at least: one of these, termed “nitro-aerial particles,” is necessary for the support of life and for the combustion of inflammable bodies; while the other, left after this constituent has been removed, is incapable of supporting either life or combustion. The portion which is necessary for life enters, during respiration, into the blood. It is the chief cause of motion in animals and in plants.
2. These “nitro-aerial particles” are also present in saltpetre or nitre, as can be shown by mixing inflammable substances, such as sulphur and charcoal, with nitre to form gunpowder, filling a tube with the powder, and, after setting it on fire, immediately plunging the open end of the tube under water. The sulphur and charcoal will be as completely consumed as if burned in the open air. Such combustion might, however, be ascribed to a “sulphureous” constituent in saltpetre; by “sulphureous” is to be understood combustible, for those substances capable of burning were imagined to contain a “sulphur” which gave them that property. That nitre does not contain such “sulphur” can be shown by exposing it alone to heat, when no change takes place, except fusion. Besides, nitre is compounded of “spirit of nitre” or nitric acid and pure alkali, neither of which contains a combustible sulphur; hence the particles of fire-air must be present in nitre in no small amount. But it is probable that it is the spirit of nitre which contains such fire-air particles, because, as will be shown later, they are not present in the alkali.
One difficulty occurs to Mayow. How is it that so large a quantity of gas as is necessary to support combustion can be contained in a relatively small bulk of saltpetre? He tries whether a solution of saltpetre evolves air-bubbles when placed in a vacuum, and finds that it effervesces less than pure water does. He also prepares saltpetre by mixing nitric acid and alkali in a vacuum; a brisk effervescence occurs, and the dried-up salt is ordinary saltpetre. Hence saltpetre cannot contain elastic air. Mayow consequently draws a distinction between “air” and “air-particles.”
The residue left after the “fire-air,” or spiritus igneo-aerius, has been removed from ordinary air by breathing or by combustion is proved to be lighter than the fire-air itself; because a mouse dies sooner if kept at the top of air in a confined bell-jar than at the bottom; and a candle goes out sooner. Here the conclusion is right, although the reason given is wrong; for it is the temperature of the respired air which makes it rise, and not the fact that it is specifically lighter than the oxygen.
Metallic antimony gains in weight when it is set on fire by a lens, and burns; if this gain in weight, Mayow remarks, is not due to the absorption of nitro-aerial particles and to the fire, it is difficult to say to what it is due.
The reason why substances burn so violently in nitre compared with air, is because of the proximity of the fire-air particles; and these are evidently due to the nitric acid, because the residue—the alkali—if mixed with sulphur and inflamed, does not produce ignition.
3. All acids contain fire-air particles, for acids have great similarity to each other. This is shown as follows:—Antimony made into a calx by the sun’s rays with a burning-glass gives the same calx as when it is evaporated repeatedly with nitric acid and converted into “Bezoar-mineral,” i.e. oxide of antimony. And iron-rust obtained from sulphide of iron appears to be formed by the union of the fire-air particles with the metallic “sulphur” of the iron.
It has up till now been believed that sulphuric acid is an ingredient of common sulphur. But this is unlikely, for sulphur has a sweetish, and not an acid taste. Moreover, quite a different substance from a vitriol (or sulphate) is obtained by melting together alkali and sulphur; and no effervescence takes place during its preparation. Sulphur, too, is precipitated out of the “liver of sulphur” (potassium persulphide) by the addition of sulphuric acid. Now, were sulphuric acid contained in sulphur, it would hinder the union of the sulphur with the alkali.
It is to be noticed that the volatile sulphuric acid, from the combustion of sulphur, is produced in the following way:—“The flame of the burning sulphur consists, like every other flame, in the violent motion of the sulphur particles with that of the nitro-aerial particles; hence the sulphur particles, at first solid, become sharp and acid, and probably form the ordinary ‘spirit of sulphur’ (sulphuric acid). If this be not so, I know not in what manner this acid can be produced; for, as has been shown, it is very improbable that it previously existed in the mass of the sulphur before its deflagration. Such a change also, in all probability, takes place in pyrites, when it is converted to green vitriol; because pyrites yields sulphur on distillation; and the green vitriol on distillation gives sulphuric acid, leaving red colcothar (iron oxide) behind.”
Similarly, nitre appears to be a triple salt, formed by the union of the fiery part of air with a salt-like substance existing in the earthy material, together forming nitric acid; and this added to earthy salts (alkali) yields ordinary nitre. “I have tried to show that all acids consist of certain saline particles rendered fluid by the nitro-aerial particles.”