For efficiency the operation must be conducted with small quantities; caking may be prevented by mixing the substance with sand or powdered pumice, or, better, with iron filings, which also renders the decomposition more regular by increasing the conductivity of the mass.
In the centre of a pumice-covered plateau from loon to 2000 ft.
Millstones and pumice were also exported, but for the former the more gritty lava of Rocca Monfina was later on preferred.
Pumice stone is also exported from Lipari (II,oio tons in 1904).
The dredge often brings up large numbers of nodules formed upon sharks' teeth, the ear-bones of whales or turtles or small fragments of pumice or other volcanic ejecta, and all more or less incrusted with manganese oxide until the nodules vary in size from that of a potato to that of a man's head.
Broken as is the surface, poor as is the soil of certain tracts, there is but little of the island which will not ultimately be cultivated with profit as pumice and clay-marl yield to labour.
Lava is much used for paving-stones in the neighborhood of volcanic districts, where pozzolana (for cement) and pumice stone are also important.
In 1886 there was a serious volcanic eruption in the outlying island of Nivafoou, and at the same time Falcon Reef, normally awash at high water, discharged sufficient scoriae and pumice to form a new island 50 ft.
Soaps are also prepared in which large proportions of fine sharp sand, or of powdered pumice, are incorporated, and these substances, by their abrading action, powerfully assist the detergent influence of the soap on hands much begrimed by manufacturing operations.'
The residual gas is then passed through a tube containing porous materials, such as woodor bone-charcoal, platinized pumice or spongy platinum, then mixed with steam and again forced through the tube.
Though, thanks to the overlaying porous pumice, the Taupo plateau is not fertile, it has a good rainfall and is drained by unfailing rivers running through deep terraced ravines.
One of these he says is found in magnesia, is white in colour, does not attract iron and is like pumice stone.
Polishing is effected by wooden wheels fed with wet pumice-powder and rottenstone and by brushes fed with moistened putty-powder.
According to an account of the natives, a violent eruption of Kilauea occurred in 1789, or about that time, and deposits of volcanic sand, large stones, sponge-like scoria (pumice) and ashes for miles around are evidence of such an eruption.
The islands have large (unworked) supplies of pumice, sandstone, sulphur, gypsum, alum and mineral-paint ochres, and some salt, kaolin and sal-ammoniac, but otherwise they are without mineral wealth other than lava rocks for building purposes.
They are mostly of volcanic origin, and include pumice, tufa, santorin earth, trass and pozzuolana itself.
Catania has a considerable export trade in sulphur, pumice stone, asphalt, oranges and lemons, almonds, filberts, cereals, wine (the total production of wine in the province amounted to 28,600,000 gallons in 1905) and oil.
The matter transported consisted of soil of various kinds - sand, ashes, fragments of lava, pozzolana and whitish pumice, enclosing grains of uncalcined lime, similar in every respect to those of Pompeii.
Of lava and pumice, with little distinction of strata, almost always confused and mingled together, and varying from spot to spot in degree of compactness.
The lagoon is slowly filling up and becoming cultivable land, but the rate of recovery from the sea has been specially marked since the eruption of Krakatoa, the pumice from which was washed on to it in enormous quantity, so that the lagoon advanced its shores from 20 to 30 yards.
Volcanic activity in the neighbourhood is further shown by the quantities of pumice-stone drifted on to the south coasts of Kandavu and Viti Levu; malachite, antimony and graphite, gold in small quantities, and specular iron-sand occur.
Almost every temple had its fetish stone on a level with the pumice stone, which is the Poseidon of the Mangaians.
It was once generally supposed that the Pliocene epoch in Nebraska was distinguished by the activity of geysers; but the so-called geyserite " now known commonly and correctly as " natural pumice " and " volcanic ash," which is found in the Oligocene and later formations, has no connexion whatever with geysers, but is produced by the shattering of volcanic rock.
This insulation generally consists of materials such as charcoal, silicate cotton, granulated cork, small pumice, hair-felt, sawdust, &c., held between layers of wood or brick, and forming a more or less heat-tight box.
The very extensive pumice deposits at Neuwied and the lava and other volcanic rocks belong to a more recent epoch.
Volcanic dust thrown into the air settles out slowly, and some of the products of submarine and littoral volcanoes, like pumice-stone, possess a remarkable power of floating and may drift into any part of the ocean before they become waterlogged and sink.
In the part of Herculaneum already excavated the corridors in the upper portions of the theatre are compactly filled, up to the head of the arches, with pozzolana and pumice transformed into tufa (which proves that the formation of this stone may take place in a comparatively short time).
Soc., 1895, 17, p. 187) manufactures it by passing the vapour of acetic acid through a rotating iron cylinder containing a mixture of pumice and precipitated barium carbonate, and kept at a temperature of from 500° C. to 600° C. The mixed vapours of acetone, acetic acid and water are then led through a condensing apparatus so that the acetic acid and water are first condensed, and then the acetone is condensed in a second vessel.
On the west of Mount Hekla this plain connects by a regular slope directly with the tableland, to the great injury of its inhabited districts, which are thus exposed to the clouds of pumice dust and driftsand that cover large areas of the interior.
Lumps of manganese oxide, with a black, shining outer surface, are also characteristic of this deposit, and frequently encrust pieces of pumice or animal remains.
Of flake charcoal and vegetable silica, or II of small pumice, are required to give the same protection as 7 in.
In Australia and New Zealand pumice, which is found in enormous quantities in the latter country, takes the place of charcoal and silicate cotton.
Larger rounded lumps of pumice, found in the clay, have probably floated to their present situations, and sank when decomposed, all their cavities becoming filled with sea water.