CAR

CAR

( 269

is dry and pulverulent like afhes, it is expedientto have recourfe to a little common fait, whichafting as a flux will begin the fufion; or if theheat is very languid fome pulverized brimftonemay be made ufe of. When the kelp has beenthus prepared and is grown cold, it is brokeninto large lumps and is fit for fale. Well madekelp is of a bluilh grey colour, fometimes ap-proaching to green ; it is of a more or lefs cel-lular texture, and contains pieces of charcoalinveloped in the mafs: when breathed on itemits a faint fulphureous odour; to the tafte itis cauftic and alkaline, mixed with the favour ofcommon fait. It yields eafily to the knife, butpofleffes a confiderable degree of toughnefs. Ifdry it is ufually covered with a white faline ef-florefcence The proportion of pure foda whichit contains varies, according to Kirwan andJamefon, k from 1.25 to 5. per cent. For theanalyfis of barilla and kelp the fame means areto be employed as have been detailed in the pre-ceding article.

Another fource of carbonated foda which wehave not yet mentioned, is common fait: butthe various methods of decompofing this fo asto obtain the alkaline bafe, either pure or com-bined with carbonic acid, belong more properlyto Muriat of Soda, to which we refer thereader.

Pure carbonated foda from whatever fub-ftance, and by whatever means it is procured,is effentially the fame. Its ufual ftate is that ofclear colourfefs cryftals, in the form of rhom-boids] odlahedrons, or oblique tetrahedral prifms.To the tafte it is fweetifh, cooling, and fubalka-line. It is foluble in i.\ times its weighty of waterat 50°, and at a higher heat diflolves in its waterof cryftallization. By expofure to the air itefflorefces, and is converted into a white mealypowder, with the lofs of a great part of itswater, and this powder when kept for fometime at a very low red heat concretes intolumps, lofes a fmall portion of its carbonic acidand all its water, and is then called defecatedfoda : in preparing this from the cryftallized car-bonat, the fait fhould be merely laid thinly on aplate at fome diftance from the fire, till it Iscompletely efflorefeed, otherwife by too fuddena heat it will diffolve in its own water, andthen is very troublefome to manage. The com-ponent parts of cryftallized carbonat of fodahave been varioufly eftimated, though the dif-ference has not been very great: we {hall men-tion the proportions as given by Bergman, andthofe adhered to by Mr. Kirwan. 1

Bergman

22

16

62

Kirw.

21.58 foda

14.42 carbonic acid

64. water of cryftalliz n

100. — 100.00

Soda, however, is capable of combining witha larger proportion of carbonic acid, by dif-folving the cryftallized carbonat in water, andthen throwing in carbonic acid gas: the cryftalsthat are now depofited will be found to containa confiderably lefs quantity of water, and theirfweetifh fubalkaline flavour will be exchangedfor a cooling faline one; fo that in this ftate itrefembles the trona. It has not, however, beenanalyzed with fuch accuracy as to enable us toftate the proportions of its ingredients.

Carbonated foda is decompofed with abftrac-tion of its bafe, by almoft all the other acids,and with abftraclion of its acid by barytes,lime, ftrontian, and potafh.

The purpofes to which carbonated foda. is ap-plied are in general the fame as thofe for whichcarbonat of potafh is ufed: the circumftancesthat induce the occafional preference of one tothe other, will be mentioned in their properplaces, efpecially in Glass making, Soapmaking, and Dying.

CARBONAT OF BARYTES.

Under the term Witherite the mineralogi-cal defeription of the native carbonated baryteswill be deferibed, and the methods of analysingthis compound.

The feveral methods of procuring the artificialcarbonat of barytes are deferibed at length underthe article Barytes .

It will be fufficient to mention in this placethat this carbonat appears by the analyfes ofKlaproth and Pelletier to be compofed (whenprevioufly dried and ignited for a few minutesin a low red heat) of 22 parts of carbonic acidand 78 parts of barytes, perhaps with a triflingportion of water.

The artificial carbonat is much more readilyfoluble m acids than the native. The muriaticor the nitric, confiderably diluted, diffolve itwith eafe, and a copious effervefcence.

Barytes has fo ftrong an affinity for the car-bonic acid that barytic water becomes coveredwith a pellicle of regenerated carbonat inftantlyon expofure to air, and breathing through itrenders it turbid and milky almoft immedi-ately. The fame efFedf takes place with lime-water, but with lefs rapidity.

k Mineralogy of Shetland, p, 193. ’ On Mineral Waters,.Table iv.