SILICA. 



Ml 



otmt<M>Ung, entire, or slightly etnarginitte, with an indexed lobe, 

 estilei, truncate, or appendaged mt the base. 



S. pralauit, Meadow IVpper-Saxifrage, hu an angular stem, supra- 

 decompound leaves, pinnate leaflet* with the segment* rather remote. 

 It is a imooth dark-green herb. The umbels consist of several unequal 

 ray- The flower* are yellowish or greenish white. The fruit is 

 roundish and ovate. It U found in damp and moist places in Englan<), 

 Europe, and Siberia, The whole plant has an unpleasant smell when 

 bruised, and is said iu some part* of Norfolk to give a bad flavour to 

 the milk of cows feeding on it, and it is generally found that cattle 

 avoid it in pastures. The species of this genus are not numerous. 



(lUbington, Manual of Britith Botany.) 



SII.KNA'CK.-K. a natural orderof Plants, belonging to the syncarp- 

 ous group of the Polypetalous sub-class of Exogens. This order is a 

 part of the larger order Caryopliyllra [CARVOI-HTLLACK.E] of Juesieu, 

 and WM originally separated by De Candolle. It has since been 

 adoped by Battling and Lindley in their systematic works. It differs 

 from the remaining portion of the order Caryophyllacta, which are now 

 called Altinacetr, in the possession of a tubular calyx, and petals with 

 claws. 



SII.K'XK, a gin us of Plants belonging to the natural order 

 Caryopkyllaeetr. It is known by its having a tubular naked 5-toothed 

 calyx ; 5 bifid unguiculate petals, which are usually crowned in the 

 throat with 5 bifid scales; 10 stamens ; 3 styles; capsules 3-celled at 

 the base, ending in 6 teeth at the apex. The species are in general 

 herbaceous, many of them annual, very few shrubby. Their stems 

 are leafy, jointed, branched, and frequently glutinous below each 

 joint. The calyx and leafstalks are also frequently viscous. The 

 leaves are opposite, simple, and entire ; the petals are mostly red and 

 white, sometimes greenish or yellowish. Some of them give off a 

 delicious perfume, especially at night. The extent of this genus is 

 very great, and constant additions are being made to it by the col- 

 lections of travellers. The greatest proportion are inhabitants of the 

 south of Europe and north of Africa. Don, in Miller's Dictionary, 

 enumerates 256 species of this genus ; of these we shall give a few 

 examples of the more common and interesting forms : 



>'. acaulit, Stemlcss Catchfly, or Moss Campion. Whole plant 

 glabrous, cespitose ; leaves linear, ciliated at the base ; peduncles 

 solitary, 1 -flowered ; petals crowned, slightly notched. It U a native 

 of Europe, and is found abundantly on the Alps. It is found on 

 nearly all the Scotch mountains, and also on Snowdon, and the highest 

 hills of Devonshire. Chamisso also gathered it on the islands of the 

 western coast of North America. The flowers are of a beautiful 

 purple colour, and it forms one of the greatest ornaments of our 

 alpine flora. Several varieties of this plant have been recorded, 

 varying chiefly in the form and existence of parts of the flower. 



>'. itijlala, Bladder-Campion or Catchfly. Stems branched ; 

 flowers numerous, panicled ; calyx inflated, netted ; petals deeply 

 cloven, scarcely any crown ; leaves ovate-lanceolate. This is a very 

 common plant throughout Europe, and is met with in almost every 

 field and wayside in Great Britain. Like most plants that are widely 

 and hugely diffused, many varieties of it have been recorded. This 

 plant has been recommended to be cultivated in the garden on account 

 of its edible properties. 



.*'. noctijlora, Night-Flowering Catchfly. Panicles forked ; petals 

 bifid ; calyx with long teeth, oblong in fruit, with 10 connected ribs ; 

 leaves lanceolate, lower ones spathulate ; whole plant clammy, pubes- 

 cent It is a native of Sweden, Germany, and Great Britain. It 

 resembles very much the common red and white campion (Lychnis 

 dioica). It is not a common plant, and is remarkable for opening its 

 flowers at night only, and in warm weather, when they exhale a 

 powerful and delicious scent. 



.*>'. ijuinquevulnerata, Five-Wounded Catchfly. 



.V. mutcipula, Spanish or Fly-Trap Catchfly. 



S.fnttitoia, Shrubby Catchfly. 



8. conpacta, Close-Flowered Catchfly. 



S. maritima, 8. Otitet, .S. Anylica, S. nutani, S. Italica, S. conica, 

 and />'. Armeria, are all British plants. 



SILKX. [SlLtCA.] 



SILICA, a compound of oxygen, and the base known to chemists 

 by the names of Silicium and Silicon. By some chemist* Silicon ii 

 regarded as a metal, and hence the termination of its name in ' urn,' 

 while others consider it as non-metallic, but more allied to boron, and 

 these adopt the term Silicon. 



Sir II. Davy, by acting upon Silica with potassium, arrived at the 

 conclusion that it was an oxide, containing a peculiar imflammable 

 base, to which he gave the name of Silicium ; the accuracy of this 

 determination has since been demonstrated by Bereelius. 



In Davy's experiments the Silica yielded its oxygen directly to the 

 potassium. 



The properties of Silicon are, that it has a dark-brown colour, no 

 lustre, and is a non-conductor of electricity : it is this latter circum- 

 stance which baa induced many chemists to question or deny the 

 property of classing it with the metal*. It is insoluble in water, and 

 incombustible in air or in oxygen gas ; it neither fuses nor undergoes 

 any other change when heated in the flame of the blow-pipe. Neither 

 the nitric, hydrochloric, sulphuric, nor hydrofluoric acid oxidises or 

 dissolves it ; but a mixture of nitric and hydrofluoric acid dissolves it 



readily, even cold. When ignited with chlorate of potash, silicon is 

 not acted upon ; but if deflagrated with nitrate of potash, the silicon 

 combines with the oxygen of the decomposed acid, and is converted 

 into silica, or silicic acid ; and this uniting with the potash of the 

 decomposed nitrate, silicate of potash is formed. 



Oxygen and Silicon form only one compound, namely, silica, or 

 silicic acid. It may be obtained artificially, but very inconveniently, 

 by deflagrating silicon with nitrate of potash. Silica exist* very 

 largely in nature; it is indeed probably the most abundant of all 

 substances whatever. [QUARTZ ; OPAL ; AOATE ; FLINT.] Kock 

 crystal is silica, nearly or quite pure, and flints or white sand 

 are but slightly intermixed with other bodies. It is artificially 

 obtained in a pure form by fusing crystal, sand, or flints, with about 

 four times their weight or carbonate of soda or carbonate of potash ; 

 the resulting fused mass is either silicate of soda or silicate of potash ; 

 the latter is a deliquescent substance, and when it has become fluid 

 by exposure to the air, has been long known by the name of Liquor of 

 Flint* : when either of these silicates is treated with hydrochloric acid 

 diluted with water, it combines' with the alkali, and with any impurity 

 which the sand or flint might contain, such as lime, alumina, or oxido 

 of iron, and precipitates the silica as a hydrate in the state of a 

 colourless gelatinous mass. It possesses the following properties : 



When recently precipitated, and while it retains the sUte of moist 

 hydrate, it is to a certain extent soluble in water, and still more so 

 in acids, and also in solution of potash or soda. When it has been 

 dried, it is an opaque white powder, inodorous, insipid, and gritty, 

 and then with more difficulty soluble in the alkaline solutions, and 

 scarcely at all so in any other acid than the hydrofluoric. It ia 

 infusible by the heat of ordinary furnaces, but by the ny-hydfOMD 

 blow-pipe it is more readily fused than lime or magnesia. Its spfrilio 

 gravity is about 27. It consists of 3 parts of oxygen, 24 ; and 1 of 

 silicon, 20 ; so that the larger proportion, by weight, of this substance 

 is oxygen. 



Although it is tasteless, and does not change vegetable blue colours 

 red, and U insoluble in water, except under the peculiar circumstances 

 mentioned, it is nevertheless by many chemists considered as and 

 classed with acids, under the name of Silicic Acid ; and the various 

 compounds which it makes with alkalies and earths, to form glass, are 

 considered as salts. Thus with potash it forms silicate of potash; 

 with soda, silicate of w>da ; ami with oxide of lead, silicate of lead ; 

 and these are all constituents of glass. China and porcelain, on the 

 other hand, may be regarded as silicates of alumina and magnesia, 

 and mortar is probably a silicate of lime. 



It is from a knowledge of the chemical properties of silicic acid 

 that the mineralogist and geologist are enabled to account for its 

 presence in so many forms in nature. It is in fact one of the most 

 generally diffused substances in nature. The circumstances of itx 

 deposit in the form of Agate*, Chert, Flint, and other minerals have 

 produced much discussion. In all these cases it is maintained by Mr. 

 Bowerbauk, that the silica has been deposited upon some kind of 

 siliceous matter at the bottom of the sea. In the case of flints the 

 spicula; of Sponges and the skeletons of Diatomaccte have been found 

 in the midst of the silica of which they are composed. It is argued 

 that it would be quite impossible that these bodies should be found 

 diffused through the substances of the flint if the ailica had been 

 deposited in a mould already formed, and that tho only explanation 

 of this circumstance is to be found in the supposition that the spicula} 

 exist in the meshes of the sponge, and that the other creatures found 

 in the midst of the sponge have been caught in its meshes. Thii 

 explanation also applies to the occurrence of the casts of molluscous 

 shells, fish-teeth, and other organic remains found in the interior of 

 flints. A'r/iini and Mvllusca are often found converted into Hint with 

 no siliceous matter surrounding thorn. These Mr. Bowerbauk main- 

 tains were first taken possession of by sponges, and that the silica has 

 been deposited in them in virtue of this condition. It is only right 

 to say here, that Mr. Bowerbank has in his collection specimens which 

 support his theory in every respect He has several recent sheila 

 which are entirely filled with sponges. If this is really the cose with 

 flints it seems equally applicable to the explanation of the formation 

 of agates and other forms of siliceous stones. We ought to add here 

 that with increased attention to the examination of agates and other 

 stones, there is no reason to believe that any of them possets n their 

 interior the remains of Mosses, Conferva, or other plants, as was at 

 one time supposed. [AGATE.] 



Silicic acid combines with the earths and metal* and forms a large 

 series of the most common as well as the rarest minerals known. 

 With lime it forms Tabular Spar. With boracic acid and lime, 

 Dot halite. With magnesia and water it forms Talc, Serpentine, Ifc- 

 phrile, .V/i i7/<r Spar, and a large number of less-known minerals. With- 

 out water, silica and magnesia form Pyroxene, Hornblende, Chrytolitc, 

 (:iu,iiilrodite, and many others. Silica, alumina, and water form 

 J/alloylile, finite, L'hlorophyllile, and the Zeolite family. The Zeolites 

 are fieuliintlitr, Apophyllite, Laumoniie, Katrolitt, Thomtonite, liar- 

 motome, Analcime, and Chabaiite. Silica, lime, and alumina form 

 I'nhnite. The anhydrous silicates of alumina are Sillimanite, Kyanitr, 

 Anilalutiit, Haurolitc, Leucite, and the Feltpar family, which includes 

 Albite, Laltradorite, ffepheline, and many minor forms of these. 



a silicate of alumina and lime. Spodwnene and Petalite 



