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.