A C I 



>)^i' oj ollitr biiJicj, flion^ly attnict, and are ftioiigly at- 

 tiactt'il. Li fad, till re is no one property peculiar lo the 

 ffcmis acid, and wliicli belongs to cacli ipecics, fo that it ii 

 not jiofTiblc to girc a dcdiution of ihc term : neverthelcfs, by 

 combining togetiicr the general dilHnguilliing qualities ol 

 acid.-, and nv)ting at tlie lame time the exccpuons to thefc, 

 a defcriptlon may be produced more illuilrativc than the 

 r.ioil laboured definition. 



PreviouHy to the confideration of the general properties 

 of acid<, it will be an advantage to give a flictch of the 

 opinions held by the old cheniilh concerning their origin 

 and mode of action, and to exa'ninc more at large the theory 

 of Lavoifur upon the fiinie fubjed. 



Wiien the meJianieal fyllem was in vogue, according to 

 which the chemical action of bodies was explained by the 

 i'uppoted fipjnrc and fizc of their refped^ive moleculx, acids 

 wcr; fnppofed to be a geniio of falts, compofed of extremely 

 fmall and iharp fpieul.u, whieh readily penetrated into the 

 .minnte!l pores of the fubllances fubjeded to their adion, 

 and thus feparated from each other their component parts ; 

 while, at the fame time, the acid became neutrahzed by its 

 points being !heathed in the pores of the body with which 

 it wa;. mixed. This explanation was, however, ably con- 

 troverted by Boyle, and by Stalil in hi.; work on falts ; and, 

 at lengtli, t(!gether with other chemical phenomena, the 

 folvent power of acids was arranged by Macquer and his 

 contcmporaWe.'', under the general laws of eledive attradion. 



After a few of the acids were difeovered, it was fuppofed 

 by Paracelfus, and feveral chemills of his age, that there 

 exiiled an univerfal faline element, or principle of acidity 

 fommon to all acids, which therefore differed from each other 

 n-hi.r in mode than elfence. Beccher, though he allowed 

 the unity of the caufe of acidity, yet affirmed it to be com- 

 fiofed of water and vitrifiable earth, and therefore not en- 

 titled to rank as an element. LStahl, in his valuable re- 

 fearchcs into the exigence of phlogifton, and the eompofi- 

 tion of fdlts, was indu;:ed to believe that the fulphuric acid, 

 or as it was then called the vitriolic, was the original acid, 

 of which all the rcil were only modifications. A fimilar 

 .opinion was h;ld by Sage and Landriani, except that the 

 former fuppofed the phofphoric acid, and the latter the car- 

 ■bonic acid, to be the primaiy one. The difcovery of de- 

 phlogifticated air, (oxygen gas) having been made by Prleft- 

 Jey in 1774, a multitude of experiments were foon after in-. 

 jlituted by the chemifts of Europe on this interelling fub- 

 ilanee ; and, in 1778, a memoir was prefentcd to the royal 

 •academy of feiences at Paris, by Lavoifier, on the compo- 

 fition of the acid of fi.:gar. In this, after having defcribed 

 the method of p:-eparing tUe acid of fugar by means of ni- 

 trous acid, he concludes, that the converfion of nitrous acid 

 into nitrous gas, is owing to the abftradion of part of its 

 oxygen l)y the fuperior afTialty of fugar for this fubftance, - 

 and that the fugar in confeqiience of its union with oxygen 

 acquires the properties of an acid. Proceeding afterwards 

 to generalize this inference, he maintains that oxygen is the 

 univerfal acidifying element, and that by combining in cer 



tain proportions with combultiblc bafes without decompof- 



ing them, it thereby converts them into peculiar acids, .comes oxy-murwlir aaa 



This dodrine, fimp'.e and elegant, and piaufible as it was, ~ 



did not _however at firll meet with general concurrence ; 

 but, i:i the courfc ofth: controverfy, it gradually ac<iuired, 

 •.ayd merited new advocates from the accumulated teftimonies 



A C I 



tlicfubjed; in this wo k he demonftrates tha' phofphoms 

 and charcoal, and fulpliur, being feparately iiillamed in 

 oxygen gas, combine with its bale, acquire an additional 

 weight equivalent to that of the air confumed, and are 

 converted into the phofphoric, carbonic, and fulphuric acids. 



Befides the fynthetical arguments above alluded to, the 

 Lavoiferian theory is fupported by an equal number of 

 analytical experiments, in which moll of the known acids 

 are decomjjofed into oxygen, and one or moi-e combullible 

 bafes. Tlie moll elegant fpe<-imen of both kinds of proof 

 is furniflied by the nitrous acid : if purified nitre, (nitrat of 

 potaPn) previoully deprived of its water of ciyllallization, 

 be expofed in a lilver retort to a low red heat, a large quar - 

 tityofgaa, confilling of oxygen and azot, in the propc r- 

 tion of about 80 of the former to 20 of the latter, v,-ill he 

 given out, and pure potafh will remain in tiie retort, whole 

 weight together with that of the gafies will be equivalent to 

 that of the original nitre ; the mixed gaffes are wholly delli- 

 tute of acid properties, but by being forced into union by 

 means of the eledric fpark, their volume is gradually dimi- 

 nilhed, and at length the whole is reduced to an acid liquor, 

 poffeffing all the qualities of nitrous acid ; if this and the 

 potafli remaining in the fird procefs be mixed together, 

 chemical union immediately eniujs, and nitre is repro- 

 duced. 



Three of the known acids arc incapable .'yf being decom- 

 pofed by any method that we arc at prefent acquainted 

 with ; it is therefore only from analogy that they are fup- 

 pofed to contain oxygen for their acidifying principle ; this 

 circumftance, however, is no peculiar objedion to tlie theory 

 of Lavoifier, for fince all the decompofiible acids may be 

 refolved into oxygen and a fimple or compound combuiiiible 

 bafe, it fcems confiftent with the principles of chemical phl- 

 lofophy to ellabliili that as a general h.v, to which in the 

 pre!ent fcatc of our knowledge, there is not a fingle excep- 

 tion. 



Subllances, whofe mutual affinity is confiderable, may 

 combine with each other in various proportions, and the re- 

 fultlng compound.s will vary in their properties accordingly : 

 this is the cafe with all the known acidifiable bafes vvhlcli 

 in their lowell ftate of oxydation exhibit no acid properties 

 vi'liatever : nor is the devclopement of an acid an evidence of 

 the compleat faturation of its bafe with oxygen, there being 

 feveral acids capable of combining with additional quantities 

 of oxygen, and thus acquiring new and more decided acid 

 charaders. — It is even fu-ppofcd that fome bafes may be 

 oxygenated in three different degrees, preferving in each the 

 elfc.uial qualllies of acids : hence rcfults an important ar- 

 rangen-.ent of acids according as they are oxygenated in the 

 iirft, fecond or third degree. The reformed chcmlcid no- 

 menclature on the principles of Lavoifier and Morveau, has 

 ingeniouOy diflinguifhed tlwfe flates by the terminations oas 

 and ic, and the prefix oxy (for oxygcnnted) ; thus lulphur, at 

 the lowell flate of oxygenat'on in wliicii it acquires acid 

 proijerties, is called J'ulphtireoiis acid ; when ftill further 

 oxygenated it becomes fu/p/jurir tidil ; thus alio, muriatic 

 acid, when raifed to the third degree of oxygenation, be- 



.tif experiment in its confirmation. — The publication of La- 

 ,vo Tier's Elements of Cli'.miflry, in i 789, contributed more 

 J^han any thing elfe to fettle the opinion of ^che;niil3 upon 



riie old cliemlflo divided acids into mineral, vegetable, 

 and animai, according to their fuppofed origin ; this, how- 

 e-er, is not only an incor.venie.it, but an incorred me- 

 thod 'of arrangement, as many of thefe bodies are found 

 in all die three natural kingdoms. Upon the whole, 

 pej-haps, the bcil way of arranging th;;;ii is the foUov/- 

 i.ig : 



States 



