The experiments here alluded to are, 1. Concerning the production of nitrous gas from dissolving iron and many other metals in nitrous acid, which though first discovered by Dr. Hales (Static. Ess. Vol. I. p. 224) was fully investigated, and applied to the important purpose of distinguishing the purity of atmospheric air by Dr. Priestley. When about two measures of common air and one of nitrous gas are mixed together a red effervescence takes place, and the two airs occupy about one fourth less space than was previously occupied by the common air alone.
2. Concerning the green substance which grows at the bottom of reservoirs of water, which Dr. Priestley discovered to yield much pure air when the sun shone on it. His method of collecting this air is by placing over the green substance, which he believes to be a vegetable of the genus conferva, an inverted bell-glass previously filled with water, which subsides as the air arises; it has since been found that all vegetables give up pure air from their leaves, when the sun shines upon them, but not in the night, which may be owing to the sleep of the plant.
3. The third refers to the great quantity of pure air contained in the calces of metals. The calces were long known to weigh much more than the metallic bodies before calcination, insomuch that 100 pounds of lead will produce 112 pounds of minium; the ore of manganese, which is always found near the surface of the earth, is replete with pure air, which is now used for the purpose of bleaching. Other metals when exposed to the atmosphere attract the pure air from it, and become calces by its combination, as zinc, lead, iron; and increase in weight in proportion to the air, which they imbibe.]
"So in Sicilia's ever-blooming shade
When playful PROSERPINE from CERES stray'd,
Led with unwary step her virgin trains
180 O'er Etna's steeps, and Enna's golden plains;
Pluck'd with fair hand the silver-blossom'd bower,
And purpled mead,—herself a fairer flower;
Sudden, unseen amid the twilight glade,
Rush'd gloomy DIS, and seized the trembling maid.—
185 Her starting damsels sprung from mossy seats,
Dropp'd from their gauzy laps the gather'd sweets,
Clung round the struggling Nymph, with piercing cries,
Pursued the chariot, and invoked the skies;—
Pleased as he grasps her in his iron arms,
190 Frights with soft sighs, with tender words alarms,
The wheels descending roll'd in smoky rings,
Infernal Cupids flapp'd their demon wings;
Earth with deep yawn received the Fair, amaz'd,
And far in Night celestial Beauty blaz'd.
[When playful Proserpine. l. 178. The fable of Proserpine's being seized by Pluto as she was gathering flowers, is explained by Lord Bacon to signify the combination or marriage of etherial spirit with earthly materials. Bacon's Works, Vol. V. p. 470. edit. 4to. Lond. 1778. This allusion is still more curiously exact, from the late discovery of pure air being given up from vegetables, and that then in its unmixed state it more readily combines with metallic or inflammable bodies. From these fables which were probably taken from antient hieroglyphics there is frequently reason to believe that the Egyptians possessed much chemical knowledge, which for want of alphabetical writing perished with their philosophers.]
195 VI. "Led by the Sage, Lo! Britain's sons shall guide
Huge SEA-BALLOONS beneath the tossing tide;
The diving castles, roof'd with spheric glass,
Ribb'd with strong oak, and barr'd with bolts of brass,
Buoy'd with pure air shall endless tracks pursue,
200 And PRIESTLEY'S hand the vital flood renew.—
Then shall BRITANNIA rule the wealthy realms,
Which Ocean's wide insatiate wave o'erwhelms;
Confine in netted bowers his scaly flocks,
Part his blue plains, and people all his rocks.
205 Deep, in warm waves beneath the Line that roll,
Beneath the shadowy ice-isles of the Pole,
Onward, through bright meandering vales, afar,
Obedient Sharks shall trail her sceptred car,
With harness'd necks the pearly flood disturb,
210 Stretch the silk rein, and champ the silver curb;
Pleased round her triumph wondering Tritons play,
And Seamaids hail her on the watery way.
—Oft shall she weep beneath the crystal waves
O'er shipwreck'd lovers weltering in their graves;
215 Mingling in death the Brave and Good behold
With slaves to glory, and with slaves to gold;
Shrin'd in the deep shall DAY and SPALDING mourn,
Each in his treacherous bell, sepulchral urn!—
Oft o'er thy lovely daughters, hapless PIERCE!
220 Her sighs shall breathe, her sorrows dew their hearse.—
With brow upturn'd to Heaven, "WE WILL NOT PART!"
He cried, and clasp'd them to his aching heart,—
—Dash'd in dread conflict on the rocky grounds,
Crash the mock'd masts, the staggering wreck rebounds;
225 Through gaping seams the rushing deluge swims,
Chills their pale bosoms, bathes their shuddering limbs,
Climbs their white shoulders, buoys their streaming hair,
And the last sea-shriek bellows in the air.—
Each with loud sobs her tender sire caress'd,
230 And gasping strain'd him closer to her breast!—
—Stretch'd on one bier they sleep beneath the brine,
And their white bones with ivory arms intwine!
[Led by the Sage. l. 195. Dr. Priestley's discovery of the production of pure air from such variety of substances will probably soon be applied to the improvement of the diving bell, as the substances which contain vital air in immense quantities are of little value as manganese and minium. See additional notes, No. XXXIII. In every hundred weight of minium there is combined about twelve pounds of pure air, now as sixty pounds of water are about a cubic foot, and as air is eight hundred times lighter than water, five hundred weight of minium will produce eight hundred cubic feet of air or about six thousand gallons. Now, as this is at least thrice as pure as atmospheric air, a gallon of it may be supposed to serve for three minutes respiration for one man. At present the air can not be set at liberty from minium by vitriolic acid without the application of some heat, this is however very likely soon to be discovered, and will then enable adventurers to journey beneath the ocean in large inverted ships or diving balloons.
Mr. Boyle relates, that Cornelius Drebelle contrived not only a vessel to be rowed under water, but also a liquor to be caried in that vessel, which would supply the want of fresh air. The vessel was made by order of James I. and carried twelve rowers besides passengers. It was tried in the river Thames, and one of the persons who was in that submarine voyage told the particulars of the experiments to a person who related them to Mr. Boyle. Annual Register for 1774, p. 248.]
[Day and Spalding mourn. l. 217. Mr. Day perished in a diving bell, or diving boat, of his own construction at Plymouth in June 1774, in which he was to have continued for a wager twelve hours one hundred feet deep in water, and probably perished from his not possessing all the hydrostatic knowledge that was necessary. See note on Ulva, Vol. II. of this work. See Annual Register for 1774. p. 245.
Mr. Spalding was professionally ingenious in the art of constructing and managing the diving bell, and had practised the business many years with success. He went down accompanied by one of his young men twice to view the wreck of the Imperial East-Indiaman at the Kish bank in Ireland. On descending the third time in June, 1783, they remained about an hour under water, and had two barrels of air sent down to them, but on the signals from below not being again repeated, after a certain time, they were drawn up by their assistants and both found dead in the bell. Annual Register for 1783, p. 206. These two unhappy events may for a time check the ardor of adventurers in traversing the bottom of the ocean, but it is probable in another half century it may be safer to travel under the ocean than over it, since Dr. Priestley's discovery of procuring pure air in such great abundance from the calces of metals.]