The effect is even perceptible at a temperature as low as 220° C. Hydrogen, and, in a much less degree, oxygen and nitrogen, will also permeate silica, but only at higher temperatures.
Thorianite, however, contains no silica, and until it is shown that metallic oxides behave in the same way this explanation must be accepted with reserve.
Some of the best sandstone in the United States is obtained from Cuyahoga and Lorain counties; it is exceptionally pure in texture (about 97% being pure silica), durable and evenly coloured light buff, grey or blue grey.
At the same time Berzelius obtained the element, in an impure condition, by fusing silica with charcoal and iron in a blast furnace; its preparation in a pure condition he first accomplished in 1823, when he invented the method of heating double potassium fluorides with metallic potassium.
Either silica or tin may be present.
If silica be present, it gives the iron bead when heated with a little ferric oxide; if tin is present there is no change.
The raw materials used in the manufacture are: (I) iron-free kaolin, or some other kind of pure clay, which should contain its silica and alumina as nearly as possible in the proportion of 2SiO 2: Al203 demanded by the formula assigned to ideal kaolin (a deficit of silica, however, it appears can be made up for by addition of the calculated weight of finely divided silica); (2) anhydrous sulphate of soda; (3) anhydrous carbonate of soda; (4) sulphur (in the state of powder); and (5) powdered charcoal or relatively ash-free coal, or colophony in lumps.
"Ultramarine rich in silica" is generally obtained by heating a mixture of pure clay, very fine white sand, sulphur and charcoal in a muffle-furnace.
- These are the materials which are utilized by the vegetable plankton in the synthesis of living material: they are water, carbonic acid, nitrates and nitrites of calcium, magnesium and other earthy and alkaline metals, phosphates, silica, traces of salts containing iron, sulphur, potassium and a few other elements.
Silica (which is required for the skeletons of diatoms, radiolaria, peridinians, etc.) is present in about the same concentration, but it is now suspected that a source of this substance may be clay washed down from the land and present in the sea in the colloidal form.
Silica is continually being added to the ocean.
The silica, in the form of diatom or radiolarian skeletons, is eventually deposited on the ocean floor after the death of the organisms. Most of the fine colloidal clay is, however, deposited as river-sludges when the fresh water carrying it mixes with denser sea-water.
High percentage of silica, low iron, lime and magnesia, and a considerable amount of potash and soda).
Clarke (1889-1893) supposes them to be substitution derivatives of normal aluminium orthosilicate A14(S104)3, in which part of the aluminium is replaced by alkalis, magnesium, iron and the univalent groups (MgF), (A1F2),(AlO), (MgOH); an excess of silica is explained by the isomorphous replacement of H 4 SiO 4 by the acid H4S130s.
Lead silicates are obtained as glasses by fusing litharge with silica; they play a considerable part in the manufacture of the lead glasses (see Glass).
The sulphates are treated with water, which dissolves the uranium and other soluble salts, while silica, lead sulphate, &c., remain; these are removed by filtration.
The theory most widely accepted at present is that glass is a quickly solidified solution, in which silica, silicates, borates, phosphates and aluminates may be either solvents or solutes, and metallic oxides and metals may be held either in solution or in suspension.
The newer glasses, on the other hand, contain a much wider variety of chemical constituents, the most important being the oxides of barium, magnesium, aluminium and zinc, used either with or without the addition of the bases already named in reference to the older glasses, and - among acid bodies - boric anhydride (B20 3) which replaces the silica of the older glasses to a varying extent.
A high silica-content tends towards both hardness and chemical stability, and this can be further increased by the addition of small proportions of boric acid; in larger quantities, however, the latter constituent produces the opposite effect.
The materials are generally used in the form either of oxides (lead, zinc, silica, &c.) or of salts readily decomposed by heat, such as the nitrates or carbonates.
A good quality of sheet-glass should show, on analysis, a composition approximating to the following: silica (SiO 2), 72%; lime (CaO), 13%; soda (Na 2 O), 14%; and iron and alumina (Fe 2 O 3, Al 2 O 3), 1%.
It is found in the form of oxide (silica), either anhydrous or hydrated as quartz, flint, sand, chalcedony, tridymite, opal, &c., but occurs chiefly in the form of silicates of aluminium, magnesium, iron, and the alkali and alkaline earth metals, forming the chief constituent of various clays, soils and rocks.
The older methods used for the preparation of the amorphous form, namely the decomposition of silicon halides or silicofluorides by the alkali metals, or of silica by magnesium, do not give good results, since' the silicon obtained is always contaminated with various impurities, but a pure variety may be prepared according to E.
Phys., 1897, (7) 12, p. 153) by heating silica with magnesium in the presence of magnesia, or by heating silica with aluminium.
Wohler, Ann., 1856, 97, p. 266; 1857, 102, p. 382); by heating silica with magnesium in the presence of zinc (L.
Gattermann, Ber., 1889, 22, p. 186); and by the reduction of silica in the presence of carbon and iron (H.
The product is a crystalline solid of specific gravity 2.34, and melts at about 1430° C. See also German Patent 108817 for the production of crystallized silicon from silica and carborundum.
On fusion with alkaline carbonates and hydroxides it undergoes oxidation to silica which dissolves on the excess of alkali yielding an alkaline silicate.
Phys., 1880, (5), 20, P. 5 Only one oxide of silicon, namely the dioxide or silica, is known.
Silicon fluoride, SiF4, is formed when silicon is brought into contact with fluorine (Moissan); or by decomposing a mixture of acid potassium fluoride and silica, or of calcium fluoride and silica with concentrated sulphuric acid.
Berzelius (Jahresb., 182 5, 4, p. 91) by the action of chlorine on silicon, and is also obtained when an intimate mixture of silica and carbon is heated in a stream of chlorine and the products of reaction fractionated.
Silicon sulphide, SiS 2, is formed by the direct union of silicon with sulphur; by the action of sulphuretted hydrogen on crystallized silicon at red heat (P. Sabatier, Comptes rendus, 1880, 90, p. 819); or by passing the vapour of carbon bisulphide over a heated mixture of silica and carbon.
The view, often repeated, that the saccharum of the ancients is the hydrate of silica, sometimes found in bamboos and known in Arabian medicine as tabashir, is refuted by Yule, Anglo-Indian Glossary, p. 654; see also Not.
Oxide of zinc, like most heavy metallic oxides, is easily reduced to the metallic state by heating it to redness with charcoal; pure red zinc ore may be treated directly; and the same might be done with pure calamine of any kind, because the carbon dioxide of the zinc carbonate goes off below redness and the silica of zinc silicate only retards, but does not prevent, the reducing action of the charcoal.
The genesis of the last three types of deposit is generally assigned to the simultaneous percolation of solutions of gold and silica, the auriferous solution being formed during the disintegration of the gold-bearing metalliferous veins.
Percy, the mineral matter being also changed by the removal of silica and alkalis and the substitution of substances analogous in composition to fire-clay.
Clearer evidence of their occurrence has, however, been found in fragments of wood fossilized by silica or carbonate of lime which are sometimes met with in coal seams.
Filtration in the chemical laboratory is commonly effected by the aid of a special kind of unsized paper, which in the more expensive varieties is practically pure cellulose, impurities like feric oxide, alumina, lime, magnesia and silica having been removed by treatment with hydrochloric and hydrofluoric acids.
Its most important property is that it rapidly attacks glass, reacting with the silica of the glass to form gaseous silicon fluoride, and consequently it is used for etching.
Proctor in 1877 directed attention to the composition of the slag resulting from the burning of esparto, which they found to be strikingly similar to that of average medical bottle glass, the latter yielding on analysis 66.3% of silica and 25.1% of alkalies and alkaline.
Of the sodium silicates the most important is the mixture known as soluble soda glass formed by calcining a mixture of white sand, soda-ash and charcoal, or by dissolving silica in hot caustic soda under pressure.
A soft, unctuous form results on treating carbon with ash or silica in special furnaces, and this gives the so-called "deflocculated" variety when treated with gallotannic acid.
Any silicate present is also converted into bicarbonate with elimination of silica, which must be filtered off.
According to the proportion of silica, the lava is distinguished as "acid" or "basic."
It is a most powerful oxidizing agent, phosphorus being readily oxidized to phosphoric acid, arsenic to arsenic acid, silicon at 250° C. to silica, and hydrochloric acid to chlorine and water.
At high temperatures it acts as a reducing agent, reducing silica to silicon, boric acid to boron, &c. (H.
One class, represented by gelatin, will redissolve on warming or diluting, while the other class, containing such substances as silica, albumen, and metallic, hydrosulphides, will solidify on heating or on the addition of electrolytes to form a solid "gel" which cannot be redissolved.
Bog iron ore is an impure limonite, usually formed by the influence of micro-organisms, and containing silica, phosphoric acid and organic matter, sometimes with manganese.
Kaolin or China clay is essentially a pure disilicate (Al 2 O 3.2SiO 2.2H 2 O), occurring in large beds almost throughout the world, and containing in its anhydrous state 2 4.4% of the metal, which, however, in common clays is more or less replaced by calcium, magnesium, and the alkalis, the proportion of silica sometimes reaching 70%.
Natural soils consist of substances derived from the decomposition of various kinds of rocks, the bulk consisting of clay, silica and lime, in various proportions.