SIL

SIL

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earth in fine powder, be boiled with a folutionof cauftic potafh or foda in which the alkalineportion is about twice the- weight of the earth,after the water has entirely evaporated thereremains a white puffy mafs .which perfeftlydiffolves in warm water into a clear folution.A fimilar folution is formed by melting the filexin a moderate red heat with about three or fourtimes its weight of dry carbonated potafh orfoda. The mixture effervefces and iwells vio-lently during the fufion, owing to the efcape ofthe carbonic acid, and at. laft, fettles into aclear glafs, which is perfectly foluble in water.A much fmaller quantity of alkali, however,is able to difiolve this earth into a perfedl glafs,,in a high heat, but this is not foluble in waterunlefs the alkali is in confiderable excefs. Thisfolution of Silicited Alkali , or Liquor Silicum,as it is fometimes called, has a ftrong, burning,alkaline tafte. When faturated with an acid itbecomes turbid, and the earth flowly feparatesin the form of a fpongy flocculent precipitate.If this is taken out without drying, and ful-phuric, nitric, or muriatic acid added to it, orif the firfl folution is at once fuperfaturatedwith the acid, the filex is rediffolved and the-liquor becomes clear. This is much affifted bylarge dilution with water, for the fame propor-tion of acid will not rediffolve the earth whenconcentrated. If this acid folution of, filex isevaporated nearly to drynefs, the whole of thefilex feparates in a gelatinous form from the,folution, and becomes as at firfl equally info-luble in any future portion of acid, fo that itmay be wallied and edulcorated without lofs.In this circumflance filex differs from alumine,for the latter is again foluble in acids withoutfurther preparation. Silex thus procured isquite white, feels dry, granular, and is per-fectly infipid.

There is however a very intimate union be-tween filex and alumine when in folutiontogether, as has been fully explained under thearticle Alumine.

Silex, even when diffolved in an acid oralkali gives no peculiar tafte, fo that the filicitedalkali has fimpiy an alkaline tafte, the fluat offilex an acid tafte, &c.

_ Both barytes and flrontian in fome degreediffolve filex as the alkalies do, but lefs exten-• e \?A ^ auc l ue hn mixed 200 parts of flrontianwith 60 of filex, a heated the mixture intenfelytor an hour m a platina crucible, and produceda grey, fonorous, rifty mafs, with only a flightcauftic tafte. When this was boiled in water,* Ann, Chin*, tom. ap, p. 37^

fome of it diffolved, though lefs than if it werepure flrontian, and it could not be cryftallized.Saturated with nitric acid, it gave by evapora-tion a copious jelly, which was pure filex.

The fame chemift alfo mixed 150 parts of ba-rytes with 50 of filex, and heated them ftronglyfor an hour in a platina crucible. The refultingmafs was of a pale apple green, forming inwater a folution of the lame colour, and withlittle tafte. This fubflance was alfo entirely fo-luble in moll of the acids, and the folution raninto a jelly by evaporation, which was pure filex.

For the effedl of alkalies on filex, fee the-article Glass .

SILICEOUS SCHISTUS. See Keisel-

SCHIEFER.

SILICITED ALKALI. See the articleSilex.

SILK.

This article is introduced in this place onaccount of a very peculiar fait or cryftallinefubflance obtained from it by the nitric acid.

Silk in its natural flate (that is, before it isbleached) contains a kind of yellow refinousmatter, which gives its fine golden colour.When raw filk is infufed in water, a portion ofgummy matter is diffolved, and a light ambercoloured liquor is produced. Pure alcoholextraUs a much deeper yellow colour, andmakes a tinfture that lofes none of its colour bylong expofure to’ the fun, which bleaches thefilk itfelf. 1

Nitrous acid a<?cs powerfully on filk in pro-portion to its concentration. If two drams ofthis acid are mixed with a pint of alcohol, b andfilk, either raw or bleached, be immerfed in it,and kept in digeftion in a moderate warmth fortwenty-four hours, the filk becomes of a dullyellowifli brown, which after rinfing and wafh-ing with foap, and drying, turns to a fine-golden yellow, which is very permanent.

But when concentrated nitric acid is diftilled-off filk, and the remaining liquor duly evapo-rated, much oxalic acid is obtained-, and therefidue if evaporated Hill further, yields along,with a little remaining oxalic acid, a quantity ofyellow granular cryftals, extremely bitter, notacid, and flaming the faliva and hands of avery deep yellow not eafily removed. If theliquor is previoufly faturated with potafh andevaporated, another yellow filky fait feparates,which detonates on coals like common nitre,and appears to be a triple combination of theformer bitter fubflance with nitrat of potafh.

The firll-mentioned granular cryftals exa»-

* ‘Ibid. An. Chim. tom. 17.- •

* Beauiue,