A L K 



friitial particulars, the refpcflive app •llations of fixst! and VO' 

 IjliU alkali have long been adopted by chMiiilh. Tor the 

 account of the procefs of" procuring thcfe lalts as an article 

 of corn'm-rcc, for their natural hillory, and other particulars, 

 wc Ihall refer the reader to the v, or'dsi Potash, Soda, and 

 Ammonia. 



The properties common to all alkalies are the following : 

 they hive a highly acrid tnile, -.vliich afts with fo much enorgy 

 upon the tongue as to produce the feni'ation ot burning, and 

 uiilefs they arc much diluted, they very foon corrode the 

 tliin Ikin which covers it, and produce a fmall efehar or dead 

 part, which, for a time, leavrs a flight fore on that fcnlible 

 organ. They have an unftuous feel to tlic finger, not from 

 any oily nature in the alkalies, butbecaufe thty direftly dif- 

 f;jlve the furface of the (l<in, and produce a kind of foap. 

 They effeft a remarkable change on fevcral vegetable colours. 

 The red of rofes, and the blue of violets, are turned by them 

 to a dull green ; the red of archill or litmus, to a blue ; the 

 yellow of turmeric, the light brown of jalap root, liquorice 

 loot, and of many other roots and woods, are all rendered 

 much deeper in colour, approaching to a brick-red. They 

 unite with fulphur, forming compounds which have the pro- 

 perty of abforbing tlie oxygen from atmofphcric air, and, 

 when moiftened, of giving out a peculiar fetid gas. 'I'hefe 

 compounds have been denominated alLaline Ivpars, or I'lvtrs, 

 and in the modern nomenclature, yw^/'K/Y.'j-. Tliey have a 

 very powerful aftion on almoft all vegetable and animal mat- 

 ters, producing fpeidy diforganization, and diflblving them 

 into a thick pulp. With oils they form the well-known 

 compound, /ou/i. They are largely foluble in water, giving 

 out heat ou union with this liquid. They imite with every 

 acid, and produce nciural fahs of various degrees of foUibi- 

 lity ; in which, when tl-.e contents are mutually faturated, 

 the diftinguilhing properties of both acid and alkali are neu- 

 fi-alized, and no longer to be perceived. Owing to the very 

 Arong affinity which they bear for acids, they decompofe 

 the acid folutions of all metals and moil earths. Thcfe are 

 the moft charafteriflic properties common to <?// alkalies ; 

 hut there are others which are confiued to one or other of 

 the two fpecies. Thefe we fhall enumerate, referring the 

 Teader for more particular information, to the individual ar- 

 ticles. 



The Volatile Alkali (Ammonia) is diflinguifhed, (as 

 its name implies) by its volatility. Thepurell form in which 

 it is known to us is that of a gas, which is permanent at 

 any degree of cold that has ever been appHcd to it, and 

 ur.ites readily with water in large quantity, from which, 

 however, it may be again expelled by a heat much below 

 boiling. It has never been procured in a folid form, unlefs 

 coTTibined with fome other fubftance ; nor as a Hquid, except 

 by its union with water. It differs remarkably from the 

 fixed alkahes in having a very pungent fmell, which highly 

 ftiniulates the noftrils, and excites coughing and tears. Ow- 

 ing to the eafe with which it affunies a gafeous form, it is in- 

 capable of uniting with many fubftances which the fixed al- 

 kalies will diffolve, wlien affiftcd by fufion in a flrong heat. 

 The volatile alkali is weaker in all itsatfuiities than the fixed. 

 It is alfo the only one which is decidedly proved to be a com- 

 pound iubflaiice ; the nature of its conlfltuent parts (which 

 are bjdrogen and azote) having been afcertaiued by nume- 

 rous experiments both of fyrithefis and analyfis. See Am- 

 monia. 



The Fixed Alkalies, (Alkali fuerhjlandiges, Laugeri' 

 falzy Germ-Alcali dlYo Ital.) are the proper //.-cii'wrj; alkalies, 

 or thofc that are procured by lixiviution of the afhes of burnt 

 vegetables. They may be obtained in a very pure folid 

 form, either cryftallized, or as a fimple concrete. Befides 

 the properties which have been mentioned as common to all 



A L K 



alkalies, thcfe poffefs confiderable fixity in fire, and at a red 

 heat they run into thin fufion. A higher heat, however, vo- 

 latilizes them, and they fly off in fenfible vapour. The fixed 

 alkalies, when in fufion, will readily diffolve filiceous earth in- 

 to the perfectly homogeneous tranfparcnt compound, glass. 

 Thev alio will diifolve by heat all the metallic oxyds, and 

 thereby receive various tints. They affill in the fufion of all 

 earthy and m.etallic admixtures, and their degree of fixity in 

 tlie fire enables them to combine more intimately than the 

 volatile alkali, with fulphur, phofphorus and charcoal. 

 \\'lien pure and folid, they are remarkably dehquefcent, ab- 

 forbing water from cveiy fuiTOunding medium ; and hence 

 they have been ufed by chemith to render the air of any vef- 

 fel in which they are confined, perfeftly dry. The fixed .al- 

 kalies are two in number, potash and soda, the former be- 

 ing procured from the alhes of all vegetables except marine 

 plants, and a few that grow near the fea fiiore, which yield 

 the latter alkah. The former is alfo termed the I'egelable 

 alkali, and the latter, (owing to its being fometimes found 

 native in the earth), is called the ?«;nfra/ alkali. The gene- 

 ral properties of thefe two alkalies were long known, and 

 they were long employed in various arts, before the circum- 

 ftances by which they are diilinguiflied were well afcertaiued, 

 and their feparate exiftence ellablifhed. The clofe rcfem- 

 blance which they bear to each other when pure, and the 

 fimilarity in all their moft remarkable chemical properties, 

 prevented a proper diilinition between them ; and it was 

 chiefly by the refearches of Pott, Duhamel and Margraaff, 

 that the nature of the two alkalies was fully explained. The 

 two neutral falts with vvhich the older chemifts were the mofl 

 familiar, nitre and fea-falt, have for their bafes, the former 

 the vegetable, and the latter the mineral alkali ; and it was 

 principally by enquiries into the properties and decompofitlon 

 of thefe neutral falts that the dilliniif nature of their alkaline 

 bafes was decided. 



Potafh and foda differ from each other in the ffrength of 

 their affinity with acids, which is greater in the former ; in 

 fome flight variation in their aftion on oils and animal fatSi; 

 but chieilv in the neutral ialts which they form with the 

 acids, which in all cafes differ in form of cry-flallization, in 

 folubihty, often in tafte, and in feveral other particulars. 



The intimate nature of the fixed alkahes is ffill unknown 

 to us. From the very flrong analogy with the volatile al- 

 kali, the component parts of which are fully eflabhibed, it 

 mull be confidered as highly probable that the fxed alkalies 

 are compounds, though their decompofitlon has not yet been 

 effeftcd by any experiments which can be allowed to be un- 

 exceptionable. Fixed alkalies have been fuppofed to be ge- 

 virated by the procefs of conibuilion of vegetables ; fince no 

 plants, even thofe whcfe aihes yield the molt of this fait, 

 contain before combuilion any fenfible quantity of uncom- 

 bined alkali. The accurate analvfes of feveral of the modern 

 chemills have however detetled, ip the native juices of plants, 

 feveral neutral falts, whofe alkaline bafes are united to an acid 

 which is eafily deflruclible by fire. But for this, and other 

 fpeculations on the natme of the fixed alkalies, we Ihall re- 

 fer the reader to the article Potash. 



Alkali ( Caiijlic or Pure). The alkaline f;Jt procured 

 from vegetable aflies, befides being mixed with other falts, 

 and with earth, is always faturated more or lefs completely 

 with fixed air, or carbonic acid; fo that the fixed alkali which 

 was the fubjeft of the experiments of all the chemifts, till 

 within a few years, was a fait compounded of carbonic acid 

 and the alkaline bafis. The beautiful experiments of Dr. 

 Black fully illullrated this point, and fhewed, that the reafon 

 of the greatly increafed cauilicity of alkalies, when mixed 

 with quick-hme, was the lofs of the carbonic acid, which had 

 paffed from the alkali to the earth. Caujlic alkalies, there- 

 fore, 



