G'EL

GEL

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the thinned and mod flexible. The preparationof ifmglafs is almofl peculiar to Ruflia/ and ismade in all places on the vad rivers of thismighty empire, where the large durgeon andother fillies of this genus are caught, as on theDnieper , the Don towards the Cafpian Sea, theVolga, Oby, Irtifli, and other Afiatico-Ruffianrivers. The bed ifinglafs is that which is pre-pared from the durgeon. The membraneswhich, when dried, form ifinglafs, are variousextenfions and proceffes of the peritoneum, butmore particularly the air-bladder, or founds,which is very large in thefe fifties. The foundswhen taken out of the filh are fird wafhedwith cold water, and expofed a little to diffenin the air. The outer Ikin is then peeled offand thrown away. The remainder is Amplycut out and loofely twided into rolls accordingto the intended fize of the daple, which arepegged down on boards, and hung up on linesto dry. No other preparation is ufed. Aninferior kind of cake-ifinglafs is made by takingall the clean ftireds of the twided fort, puttingthem in a flat metal-pan with a very littlewater, and heating jud enough to make a co-hering mafs. This is afterwards dried. Itwould be tedious to enumerate the minutevarieties of ifmglafs or fifti gelatin.

Good ifinglafs is edeemed the fined andpured fpecimen of animal gelatin. It is en-tirely without fade or fmell, when foaked inwater it fwells, foftens, and if held up to thelight is agreeably opalefcent to the eye. Itreadily and totally diffolves in warm water,forming the cleared and mod colourlefs of allthe known jellies. The finer forts are muchtoo valuable to be ufed for the ordinary pur-pofes of a fize or cement, but are principallyemployed in confectionary, in clarifying wines,and other purpofes of the table.

When the jelly of ifinglafs is much concen-trated by evaporation, it forms a delicate ce-ment for joining glafs, &c. for which its greattranfparency and freedom from colour render ithighly valuable. The coarfer fort of fifh-gluecake, or that which confids of refufe bits ofifinglafs, brought to a cohering mafs by water,is often ufed for the fame purpofes as commonglue. This when foul and blackened is bleachedby expofure to the vapour of fulphur, e which,on account of the loofe fibrous texture is ableto penetrate it fufficiently, an effect whichcould not take place with the folid cakes ofcommon glue.

Animal Mucilage.

In fome parts of the body of man and differentanimals is found a fomewhat clammy, infipid,whitifh or often colourlefs liquor, uncoagulableby heat, but leaving after a gentle evaporation todrynefs a fmallproportion of flimy tenacious mat-ter, much refembling gelatin in appearance, andin being equally again foluble in water. Thefaliva is perhaps the bed example of fimpleanimal mucilage in the human body, but it isfound more copioufly in other animals, as forexample, in the oyder, and many marine inha-bitants.

Animal mucus or mucilage differs howeverfrom gelatin in being readily foluble in coldwater, and efpecially in having no proper gela-tinizing power, that is to fay, a hot folutiondoes not diffen, or approach apparently moreto the folid date by cooling, but its degree ofvifcidity depends limply on the proportion ofwater in the folution without regard to tempe-rature.

Mr. Hatchett confiders mucus, however, asa fpecies of gelatin the lowed in the cohefivepow r er, or at one extremity of the fcale of tena-city, at the other extremity of which is thediffed glue from condenfed Ikin.

But Dr. Bodock has given the followingdiltinctive marks which certainly edabliftl asclear a difference between mucus and gelatin asexids between many other fubdances dronglyrefembling each other, but which have beenallowed a feparate place. The mucus of anoyder was detached by agitation in cold waterfor a few minutes, when the fluid was filteredand appeared flightly opake and gelatinous. Byevaporation it appeared that it had diflolvedabout of its weight of animal matter. Aquantity of this diluted with as much waterwas tried with the following reagents : a folu-tion of corrofive mercurial muriat producedno effect; the infufion of tan (from galls) afterfome time produced a flight turbialnefs, and atlength a fmall quantity of a precipitate. Theaqua lithargyri acetati (or vinegar faturatedwith litharge at a boiling heat) gave an imme-diate opacity, and, after fome time, a denfewhite precipitate.

The fird of thefe teds, the mercurial folution,is found to precipitate albumen only, and asno effect was here produced, it Oiews the ab-fence of this principle. The folution of tanoccafioned only a very flight opacity, but byprevious experiments it was found that a folu-

* Toekc’s Ruffian Empire. Alfo Jackfon in Phil. Tranf. vol. Ixiii.

• Pelletier.