Silica Sentence Examples

Silica is continually being added to the ocean.

Either silica or tin may be present.

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.

The atomic weight of silicon has been determined usually by analysis of the halide compounds or by conversion of the halides into silica.

The metal as prepared by electrolysis generally contains traces of aluminium and silica.

The American bauxites contain from 38 to 67% of alumina, from 1 to 23% of ferric oxide, and from 1 to 32% of silica.

After two or three hours the liquid is diluted till its density falls to 1.23, when it is passed through filter-presses to remove the insoluble ferric oxide and silica.

Much the same is true of the heat needed for the deoxidation of the silica,.

In the basic Bessemer process, also, unforeseen variations in the siliconcontent are harmful, because the quantity of lime added should be just that needed to neutralize the resultant silica and the phosphoric acid and no more.

As the essential difference between cast iron on one hand and wrought iron and steel on the other is that the former contains necessarily much more carbon, usually more silicon, and often more phosphorus that are suitable or indeed permissible in the latter two, the chief work of all these conversion processes is to remove the excess of these several foreign elements by oxidizing them to carbonic oxide CO, silica S102, and phosphoric acid P 2 0 5, respectively.

As the iron oxide is stirred into the molten metal laboriously by the workman or "puddler " with his hook or "rabble," it oxidizes the silicon to silica and the phosphorus to phosphoric acid, and unites with both these products, forming with them a basic iron silicate rich in phosphorus, called " puddling " or " tap cinder."

But this basicity implies that for each part of the silica or silicic acid which inevitably results from the oxidation of the silicon of the pig iron, the cinder shall contain some three parts of iron oxide, itself a valuable and expensive substance.

But the strong deoxidizing conditions needed in the blast-furnace to remove sulphur tend strongly to deoxidize silica and thus to make the pig iron rich in silicon.

In this process molten pig iron with much silicon but little sulphur has its silicon oxidized to silica and thus slagged off, by means of a blast of air playing on the iron through a blanket of burning coke which covers it.

The slag, in order that it may have such an excess of base that this will retain the phosphoric acid as fast as it is formed by the oxidation of the phosphorus of the pig iron, and prevent it from being re-deoxidized and re-absorbed by the iron, should, according to von Ehrenwerth's rule which is generally followed, contain enough lime to form approximately a tetra-calcic silicate, 4CaO,S10 2 with the silica which results from the oxidation of the silicon of the pig iron and tri-calcic phosphate, 3CaO,P205, with the phosphoric acid which forms. The danger of this " rephosphorization " is greatest at the end of the blow, when the recarburizing additions are made.

This lime is charged in the form of common quicklime, CaO, resulting from the calcination of a pure limestone, CaCO 3, which should be as free as possible from silica.

The usual composition of this slag is iron oxide, i o to 16%; lime, 40 to 50%; magnesia, 5%; silica, 6 to 9%; phosphoric acid, 16 to 20%.

Further objections to the presence of silicon are that the resultant silica (1) corrodes the lining of the converter, (2) makes the slag froth so that it both throws much of the charge out and blocks up the nose of the converter, and (3) leads to rephosphorization.

But Massenez and Richards, following the plan outlined by Pourcel in 1879, have found that even 3% of silicon is permissible if, by adding iron ore, the resultant silica is made into a fluid slag, and if this is removed in the early cool part of the process, when it attacks the lining of the converter but slightly.

At this time the slag is temporarily rich in iron oxide and silica, resulting from the oxidation of the iron and of its silicon as the charge slowly melts and trickles down.

In the basic open-hearth process, on the other hand, silicon is harmful because the silica which results from its oxidation not only corrodes the lining of the furnace but interferes with the removal of the phosphorus, an essential part of the process.

This slag is formed by melting lime and iron oxide, with a little silica sand if need be.

Next the metal is covered with a very basic slag, made by melting lime with a little silica and fluor spar.

It is necessary that it should be as pure as possible since the commercial product usually contains traces of ferric, manganic and aluminium oxides, together with some silica.

Sodium and potassium carbonates are valuable for fluxing off silica; mixed with potassium nitrate sodium carbonate forms a valuable oxidizing fusion mixture; "black flux" is a reducing flux composed of finely divided carbon and potassium carbonate, and formed by deflagrating a mixture of argol with 4 to 2 its weight of nitre.

Borax is very frequently employed; it melts to a clear liquid and dissolves silica and many metallic oxides.

Litharge and red lead are used in silver and gold assays, acting as solvents for silica and any metallic oxides present.

The mineral is fused with potassium carbonate, and, on cooling, the product is treated with sulphuric acid, the excess of which is removed by evaporation; water is then added and the silica is filtered off.

By modern mineralogists the name chalcedony is restricted to those kinds of silica which occur not in distinct crystals like ordinary quartz, but in concretionary, mammillated or stalactitic forms, which break with a fine splintery fracture, and display a delicate fibrous structure.

It is rather softer and less dense than crystallized quartz, its hardness being about 6.5 and its specific gravity 2.6, the difference being probably due to the presence of a small amount of opaline silica between the fibres.

Chalcedony occurs as a secondary mineral in volcanic rocks, representing usually the silica set free by the decomposition of various silicates, and deposited in cracks, forming veins, or in vesicular hollows, forming amygdales.

Devon, is known as "orbicular silica" or "beekite," having been named after Dr Henry Beeke, dean of Bristol, who first directed attention to such deposits.

This silt consists largely o alumina (about 48%) and calcium carbonate (18%) with smalle quantities of silica, oxide of iron and carbon.

The blue or green color was made by fritting together silica, lime, alkaline carbonate and copper carbonate; the latter varied from 3% in delicate blues to 20% in deep purple.blues.

The silica was needed quite pure from iron, in order to get the rich blues, and was obtained from calcined quartz pebbles; ordinary sand will only make a green frit.

Excepting where the thallus is impregnated with silica, as in Diatomaceae, or carbonate of lime, as in Corallinaceae,Characeae and some Siphonales, it is perhaps not surprising that algae should not have been extensively preserved in the fossil form.

If, however, such "fat" lime is mixed in the presence of water, not with sand but with silica in an active form, i.e.

The mixture of the lime and active silica or silicate is a pozzuolanic cement.

The simplest of all pozzuolanic cements would be a mixture of pure lime and hydrated silica, but though the latter is prepared artificially for various purposes, it is too expensive to be used as a cement material.

A similar obstacle lies in the way of using a certain native form of active silica, viz.

Cements of the Portland type differ in kind from those of the pozzuolanic class; they are not mechanical mixtures of lime and active silica ready to unite under suitable conditions, but consist of definite chemical compounds of lime and silica and lime and alumina, which, when mixed with water, combine therewith, forming crystalline substances of great mechanical strength, and capable of adhering firmly to clean inert material, such as stone and sand.

The commonest of such substances in England are chalk and clay, but where local conditions demand it, limestone, marl, shale, slag or any similar material may be used, provided that the correct proportions of lime, silica and alumina are maintained.

Thus the silica may range from 19 to 27%, the alumina and ferric oxide jointly from 7 to 14%, the lime from 60 to 67%.

All such variations are permissible provided that the quantity of silica and alumina is sufficient to saturate the whole of the lime and to leave none of it in a "free" condition, likely to cause the cement to expand after setting.

The function of the ferric oxide present in ordinary cement is little more than that of a flux to aid the union of silica, alumina and lime in the clinker; its role in the setting of the cement is altogether secondary.

This limestone consists of calcium carbonate most intimately intermixed with very finely divided silica.

It contains but little alumina and oxide of iron, which are the constituents generally necessary to bring about the union of silica and lime to form a cement, but in spite of this the silica is so finely divided and so well distributed that it unites readily with the lime when the limestone is burned at a sufficiently high temperature.

The metals, which by combination with oxygen became oxides, were antimony, silver, arsenic, bismuth, cobalt, copper, tin, iron, manganese, mercury, molybdenum, nickel, gold, platinum, lead, tungsten and zinc; and the "simple earthy salifiable substances" were lime, baryta, magnesia, alumina and silica.

The operation is finished when all the sodium sulphide has been converted into normal sodium carbonate, partly also into acid sodium carbonate (bicarbonate) NaHCO 3; at the same time a precipitate is formed, consisting of ferrous sulphide, alumina and silica, which is removed by another settling tank, and the clear liquor is now ready either for boiling down in a " fishing-pan " for the manufacture of white soda-ash, or for the process of causticizing.

On boiling gelatinous silica with ammonium polytungstate and evaporating with the occasional addition of ammonia, ammonium silicodecitungstate is obtained as short rhombic prisms. On adding silver nitrate and decomposing the precipitated silver salt with hydrochloric acid, a solution is obtained which on evaporation in a vacuum gives the free acid as a glassy mass.

The Hartville ores are remarkable for their high grade and purity, running from 60 to 70% metallic iron, with 22 to 5% silica, and only traces of sulphur and phosphorus.

The roasted ore is then smelted to a mixture of copper and iron sulphides, known as copper " matte " or " coarse-metal," which contains little or no arsenic, antimony or silica.

But as the slag carries on an average 46% of silica, it is only through the utmost skill that it can be made to run as low on an average as 0.3% in copper oxide.

Practice, however, in treating copper matte differs essentially from the treatment of pig iron, inasmuch as from 20 to 30% of iron must be eliminated as slag and an equivalent quantity of silica must be supplied.

At Tilt Cove, Newfoundland, the Cape Copper Company smelted copper ore, with just the proper proportion of sulphur, iron and silica, successfully without any fuel, when once the initial charge had been fused with coke.

The chief impurities are basic salts of iron, free iron, graphite, and sometimes silica, antimony and iron arsenates.

Mintz and others had proved that nitrification was promoted by some organism, when Winogradsky hit on the happy idea of isolating the organism by using gelatinous silica, and so avoiding the difficulties which Warington had shown to exist with the organism in presence of organic nitrogen, owing to its refusal to nitrify on gelatine or other nitrogenous media.

The glass industry was introduced from Venice in the 13th century and soon attained a vast importance; the factories are in the neighbourhood of the mountains, where minerals, and especially silica and fuel, are plentiful.

The salts of iron, copper, &c., are then dissolved in water and filtered from the insoluble silica, lead sulphate, and calcium sulphate, which are washed with dilute sulphuric acid.

His attempts to decompose "alum me, silica, zircone and glucine" were still less fortunate.

The exterior of the culms is more or less concealed by the leaf-sheaths; it is usually smooth and often highly polished, the epidermal cells containing an amount of silica sufficient to leave after burning a distinct skeleton of their structure.

Tabasheer is a white substance mainly composed of silica, found in the joints of several bamboos.

The various forms of silica have attracted attention from the earliest times, and the water-clear crystallized variety was known to the Greeks as KOo-raXXos (clear ice), being supposed by them to have been formed from water by the intense cold of the Alps; hence the name "crystal," or more commonly rock-crystal, applied to this variety.

Crystals of quartz may be readily prepared artificially by a number of methods; for example, by heating glass or gelatinous silica with water under pressure.

For other forms of silica see OPAL and TRIDYMITE.

At the temperature of the furnace the silica (sand) attacks the calcium phosphate, forming silicate, and setting free phosphorus pentoxide, which is attacked by the carbon, forming phosphorus and carbon monoxide.

This Missouri tripoli is a finely decomposed light rock, about 98% silica, and is used for filter stones and as an abrasive.

Silica forms nearly the whole substance of flint; calcite and dolomite may occur in it in small amounts, and analysis has also detected minute quantities of volatile ingredients, organic compounds, &c., to which the dark colour is ascribed by some authorities.

Microscopic sections show that flint is very finely crystalline and consists of quartz or chalcedonic silica; colloidal or amorphous silica may also be present but cannot form any considerable part of the rock.

It has been suggested that this change is due to the removal of the colloidal silica in solution, leaving behind the fibres and grains of more crystalline structure.

The silica was derived from the tests of radiolaria and the spicular skeletons of sponges.

Their silica ranges from about 60 to 45%, varying in accordance with the amount of quartz and alkali-felspar present.

They must contain little alkalis, lime, magnesia and iron, but some of them are comparatively rich in silica.

Among such substances are fireclay and firebricks, certain sandstones, silica in the form of ganister, and Dinas stone and bricks, ferric oxide and alumina, carbon (as coke and graphite), magnesia, lime and chromium oxide - their relative importance being indicated by their order, the last two or three indeed being only of limited use.

This supposes them to be free from metallic oxides forming easily fusible compounds with silica, such as lime or iron, the presence of the former even in comparatively small proportion being very detrimental.

Silica is used in furnace-building in the forms of sand, ganister, a finely ground sandstone from the Coal Measures of Yorkshire, and the analogous substance known as Dinas clay, which is really nearly pure silica, containing at most about 2-1% of bases.

In an oxidizing atmosphere it is indifferent to silica, and therefore siliceous bricks containing a considerable proportion of ferric oxide, when used in flues of boilers, brewers' coppers, &c. and similar situations, are perfectly fire-resisting so long as the heated gas contains a large proportion of unconsumed air.

The latter, especially when brought to the burning point at a high temperature, produces a heat that can be resisted by the most refractory substances only, such as silica, alumina and magnesia.

An inclined channel feeds the silica abrasive to the surface of the test wheel about 2 cm in front of the test-piece.

More than 2.4 m 2 of silica aerogel capture cells have been flown todate.

The process starts with a laser beam or electron beam writing a pattern on fused silica or silicon.

In geology, the cement of breccias and conglomerates is usually silica, iron oxides or calcite (mineral calcium carbonate ).

Such particles can include small pieces of silica, pollen grains, fungal hyphae and other organic detritus 1.

With vacuum regenerated adsorption dryers, the heat resisting drying medium silica gel forms the uniform filling material right through.

It also contains silica, which can help restore elasticity to the body's tissues.

Two of the four HSC mixtures contained silica fume.

In TLC the sample to be analyzed is spotted onto the bottom of a plate coated with a thin layer of silica gel.

Silica - gentle spherical microspheres to stimulate oxygenation and exfoliation before breaking down and disappearing.

Mr Wardlaw worked in a foundry for eight years and was exposed to silica dust and contracted pneumoconiosis.

Polyhedral models of silica polymorphs Silica, SiO 2, exists in a number of different crystalline forms.

The bottom of the tank can then be covered with a mixture of silica sand and coral sand to a depth of 2-3 cm.

Usually the ores are mixed into rocks which contain silica.

Core fills were cast using Araldite 20/20 epoxy resin tinted and bulked using fumed silica and dry powder pigments.

The fumed silica, however, is quite hard.

These methods were then applied to develop and test hypotheses about the impact on exposure patterns of respirable silica and dust.

Aerogel is made by high temperature and pressure critical point drying of a gel composed of colloidal silica structural units filled with solvents.

However, there are some concerns regarding the susceptibility of RCA to alkali silica reaction (ASR ).

Visual monitoring is facilitated by passing the air through a transparent tube containing silica gel mounted on the control panel.

It consists of special plugs that you install in place of the spark plugs, using silica gel to keep the chambers dry.

The finest pore metal foams can be made using silica micro balloons 100 or 30 microns across in aluminum silicon alloys.

Silicosis compensation You could be entitled to silicosis compensation You could be entitled to silicosis compensation if you have been exposed to silica dust at work.

Sol-gel processes are used in industry for the large-scale preparation of silica gels and colloidal sol-gel processes are used in industry for the large-scale preparation of silica gels and colloidal sols.

The horsetails are remarkable for the large quantity of silica they contain in the cuticle (hence their value in polishing), which often amounts to half the weight of the ash yielded by burning them; the roots contain a quantity of starch.

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.

The coarser particles of the sediments are deposited near the shore as gravels, sand and muds, but the very fine particles remain in suspension in the colloidal form, and some of this may be acted upon by marine bacteria or (it is surmised) even utilized by diatoms as a source of silica.

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).

By the weathering of silicates, silica passes into solution and quartz is deposited as a secondary product in the cavities of basic igneous rocks, and in fact in the crevices and along the joints of rocks of almost all kinds.

The scabbling of concrete generates silica dust and should be avoided where possible.

The Stove enamel is believed to be mixed with a silica based paste and is probably too thick.

He also used silica gel crystals to absorb the moisture.

There is no silica sand in the Medway area.

This will minimize the risk of carrying silica dust on your clothes.

Cement contains up to 5% silica in the form of free silicon dioxide which causes lung scarring known as silicosis.

Obtain some silica gel crystals which are available from craft shops.

A very dry environment (for metals) can be created by placing bagged silica gel in the polyethylene box with the finds.

Silicosis compensation You could be entitled to silicosis compensation if you have been exposed to silica dust at work.

Sol-gel processes are used in industry for the large-scale preparation of silica gels and colloidal sols.

Break edges color filled with Fynebond resin bulked with fumed silica and tinted with dry powder pigments to tone with the original glaze.

In this case, Wachs chose to use titanium compounds to tailor the electron density of clusters of vanadium oxide on a silica support.

It does not contain sodium bentonite or silica dust, and is virtually track free.

The dust in bentonite is silica, a material that has been shown to create lung issues for both humans and felines.

This becomes an issue because silica (an ingredient of glass) causes silocosis in humans, and can also cause the same lung condition in cats.

Instead of being made from clay, newspaper or silica, World's Best is made from whole kernel corn.

It is also silica and bentonite free, easing concerns of illnesses that might be created by those ingredients.

Silica cat litter is a popular alternative to traditional clay clumping litter.

Silica litters have some advantages over bentonite clay litters and brands that boast biodegradable claims, but the silica litter variety has been scrutinized in the past for safety issues.

Silicon is a naturally-occurring element that, when compounded with oxygen, forms silicon dioxide (also known as silica).

These silica crystals are used to make an effective cat litter based on their highly absorbent qualities.

Silica litter is also known as crystal litter, and these crystals are comprised of the solidified silica gel.

Each individual crystal can absorb a vast amount of fluid, wand this is why silica makes such a great cat litter.

Silica crystals are also reported to reduce litter tracking, which is very common with clay and other litter types.

Based on these admirable qualities, it's easy to see why many pet product manufacturers have leaped onto the silica boat and produced this type of cat litter.

Just as clay litter has been scrutinized for its potentially detrimental health effect, silica has been judged in an equally severe manner.

In fact, silica may pose a greater theoretical threat than clay litters.

Silica litters have often been touted as a safer alternative to clay litters.

For these reasons, clay is sometimes pushed aside in favor of silica litters.

According to the Office of Environmental Health Hazard Assessment, silica had been classified under California's Proposition 65 as a material that is known to cause cancer.

Although silica was granted a safe issuance for cat litters, the question remains as to why a chemical that has been classified as carcinogenic could possibly be declared safe to use in cat litter.

You can read the Office of Environmental Health Hazard Assessment's release regarding the stipulations and safety issues of crystalline silica at the official OEHHA site.

Silica cat litter doesn't really form a litter dust in the same fashion as bentonite clay litters.

Although silica may cause respiratory distress when breathed, it is more difficult to inhale into the lungs.

The real danger of silica litters comes with ingestion.

However, small kittens often explore the world through taste, and so silica litter may pose a health threat for inexperienced young cats.

Adult cats who suffer from a condition known as "pica" should not use silica cat litter or any litter that is dangerous when ingested.

Pica is a condition that prompts cats to ingest inappropriate materials, and silica is very dangerous when ingested.

Many of these products contain silica. which is also generating its fair share of controversy.

This type of litter, comprised of scrap bits from pine lumber, has many advantages over the popular clay and silica litter varieties.

Clay and silica cat litters are still the dominant types in the world of kitty litter.

Silica doesn't form the dust particulate of clay varieties.

However, silica isn't theorized to be much safer since this crystalline compound has been known to cause cancer.

Although experts say silica cat litters are safe as long as they are not ingested, the very concept of having a known carcinogen in close contact with a cherished pet makes some pet owners uneasy.

Moreover, although silica is extremely absorbent, some cat owners have reported cases of urine collecting at the bottom of the litter pan and causing excessive odor.

Hence, silica has failed to meet the highest standards as a cat litter.

Pine litter can be rough on the delicate pads of a cat's feet, feet that have become accustomed to the softer clay and silica pellets that previously lined their boxes.

Silica Crystals - These crystals are very absorbent and absorb odors better than the other types of litter.

Crystal litter is made from baking soda or silica gel, a derivative of sand.

Silica gel crystals are popular because they absorb a great deal of liquid, and make it possible for cat owners to "scoop out" urine when they scoop feces from the litter box.

Generally, if a cat owner scoops the chunks of urine-soaked silica gel and feces from the box on a regular basis, the litter box can be emptied and refilled less frequently.

Some owners are concerned that their cats may ingest silica gel when they lick their paws during grooming.

Most breeders recommend avoiding the use of crystalline cat litter for gestating females because of the risk that the silica gel could come in contact with the newborn kittens.

Cat litter comes in many varieties from clumping clays or silica to more naturally-derived options such as corn or pine-based products.

Even silica litters have been said to cause respiratory irritation, so they may not be the best option over pine and corn varieties.

These include talc to provide softness and smoothness, and Silica which helps to absorb oils from the skin.

Colgate Total Advanced Whitening combines the proven 12 hour germ-fighting formula of Colgate Total with an advanced whitening silica system that helps remove surface stains for healthier and whiter teeth.

With Colgate Total's advanced whitening silica system, it is a healthier way of whitening your teeth.

Silica gel can also be used for do it yourself wedding flower preservation.

Simply place the flowers in an airtight container and completely cover them with the silica gel before closing the container.

Like other glass products, smalti is composed of mostly silica, but then melted with potassium chlorate or sodium.

You can also use a pile of Silica packets that are found in shoes or clothes.

Submerge the phone in the rice or silica and let the phone sit overnight.

It has been found that certain minerals, including magnesium, sulfur, silica, and zinc are also important for maintaining healthy hair.

Also bear in mind that minerals such as silica, which is found heavily in the herb horsetail, can make a powerful difference to your hair.

Silica supplements, such as that sold by Alta Health Products, are made from extract of horsetail or Equisetum Arvense.

Alta Sil-X Silica contains silica horsetail extract, extracted with a patented process.

Silica is a trace mineral that plays an important part in bone, cartilage, connective tissue and skin formation.

Alta Health Silica uses European Horsetail extract.

This contains bioflavonoids and Alta Health Silica provides the pure organic form of soluble/colloidal silica.

Alta Potassium Chloride Plus Silica is an easily absorbed form of potassium.

This product provides a 30-day supply of packets of supplements that support skin, hair and nails such as beta carotene, Horsetail and Silica.

This supplement contains vitamins C, D2, E, B1, B2, B3, B6, B12, folic acid, iodine, zinc, copper and magnesium, along with PABA, Fenugreek, Aloe Vera and silica.

Silica is a mineral derived from nature.

Nectifirm also combines plant-based moisturizers such as bamboo, silica, English pea extract and glucosamine to further stimulate the body's production of collagen, elastin and hyaluronic acid.

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.

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.

If silica be present, it gives the iron bead when heated with a little ferric oxide; if tin is present there is no change.

Lead silicates are obtained as glasses by fusing litharge with silica; they play a considerable part in the manufacture of the lead glasses.

Wohler, Ann., 1856, 97, p. 266; 1857, 102, p. 382); by heating silica with magnesium in the presence of zinc (L.

On fusion with alkaline carbonates and hydroxides it undergoes oxidation to silica which dissolves on the excess of alkali yielding an alkaline silicate.

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.

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."

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%.

If, according to the present method of winning the metal, a bath containing silica as well as alumina is submitted to electrolysis, both oxides are dissociated, and as silicon is a very undesirable impurity, an alumina contaminated with silica is not suited for reduction.

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.

For the preparation of yttrium compounds the best raw material is gadolinite, which, according to Kiinig, consists of 22.61% of silica, 34.64.

The great hardness of teak is due to the silica deposited in the heart-wood, and the special coloring matters of various woods, such as satinwood, ebony, &c., are confined to the heart-wood.

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.

The discovery of boron by Gay Lussac and Davy in 1809 led Berzelius to investigate silica (silex).

In the following year he announced that silica was the oxide of a hitherto unrecognized element, which he named silicium, considering it to be a metal.

The source of the carbon of organic tissues is carbonic acid; that of the nitrogen in the proteids is the nitrates, nitrites and salts of ammonia dissolved in sea-water; the material of the shells or other skeletons is the silica, phosphate and calcium of the salts of sea-water (and, in rare cases, the salts of strontium).

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.

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.

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.

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.

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 French bauxites are of fairly constant composition, containing usually from 58 to 70% of alumina, 3 to 15% of foreign matter, and 27% made up of silica, iron oxide and water in proportions that vary with the colour and the situation of the beds.

The water of most of the springs and geysers holds silica in solution in considerable quantities, so that as it cools and evaporates it deposits a dazzling white sinter which has covered many square miles of the valleys and contrasts strongly with the dark green of the surrounding forests.

Of these the silica and alumina are chiefly those which the gangue of the ore and the ash of the fuel introduce, whereas the lime is that added intentionally to form with these others a slag of the needed physical properties.

The use of the first two is restricted, as they are suited only for galena ores or mixtures of galena and carbonate, which contain not less than 58% lead and not more than 4% silica; further, ores to be treated in the ore-hearth should run low in or be free from silver, as the loss in the fumes is excessive.