Obfcrvatiom on Alum, ^ ai* 



lime, employed inflead of pot-afh or ammoniac in the treatment of the mother waters, do 

 tlot favour the cryftallization of the alum, ought to have produced a change in the general 

 opinion refpedling the a£tion of pot-a(h or ammoniac *. This learned chemifl had lilce- 

 wife afcertained, that feveral alums decompofed by ammoniac afforded by evaporation th« 

 true fulphate of pot-afh, the bafis of which might be afforded, according to him, either from 

 the argillaceous earth in which vegetables had been decompofed, or from the wood-afhes 

 intentionally added, or, laflly, from a cafual mixture during the calcination of the ores* 

 And he concluded from thefe obfervatlons, that the fulphates of pot-a(h and "of alumine 

 unite together in the ftate of a triple fait ■\. 



Though Bergman appears to fufpedl that pot-a(li -Is neceffiry to the formation of alumj 

 yet he does not venture to affirm it ; as may eafdy be feen in the courfe of his differtation : fo 

 that this queflion remained ftill undecided. In faft, we fee by another paffage \, that Berg- 

 man falls into the common opinion, by confining the effecl: of the alkalis to the fimple fatu- 

 ration of the excefs of acid, exiftiiig, according to him and all other authors, in the aluminous 

 waters; and even by confidering the new falts formed by thefe alkaline fubdances as foreign 

 bodies, lefs noxious in faft than the excefs of acid, but which cannot however be fold for 

 alum §. 



If the only effe£l of alkalis in the management of aluminous lixivia were to faturate tli.i 

 excefs of acid they are fuppofed to contain, it is evident that any other fubftance capable of 

 abforbing this acid would anfwer the fame purpofe. But experience has proved the con» 

 trary, and it has been long known that this remarkable property belongs exclufively to pot- 

 afli and ammoniac. 



In order to explain this obfcure circumftance by experiment, I diffolved very pure alumina 

 in fulphuric acid of equal purity. I evaporated the folunon feveral times fucceffively, even 

 to drynefsjfor the purpofe of expelling the fupernbundant acid. I rediffolved the dry and 

 pulverulent refidue in water, and reduced the folution to different degrees of fpecific gravity, 

 with a view to feize the point mofl favourable to cryftallization : but whatever precautions i 

 took, I could not obtain any thing but a magma formed of faline plates without confiftenc-j 



* Notatu digmim eft, quod hoc ciyftallifationis obdaculum alcali volatili asqui- tollatur, non vero alcali mine-- 

 rail ct calce. Bergman de ConfudV. Aluminii, pag. 325, torn. i. Opufcula. 



+ Koc alcali quod incft, vel ex ipfa argilla repetcnJuin qua vegctabilium putrcfaHoaim rc-fiiluis fuit inqur 

 naia, vclcx cincribus Iludio additis, vel denique fub calcinationc ct uftionc fortulto immixtis. Intcrca hinc con. 

 ftat, quod alumcn ct alcali vegetabile vitriolatum facile connubium ineant, quo fal oritur triplex. Berg. ibiJ. 



t A llata momenta fufpir.ionem movent, quod alcali vegetabile alumine pcrficicndo fir neceiTarium, ideoque 

 •mnc alumen pcrfeftum inftar falis triplicis rcrpiciendutn : i'ed li*c conjei^tura vacillat; nam cadem pcrfcftio alcali ■ 

 volatili ct fpontaiica evaporationc obtinetur. Nun tamcn improbandam puto additiunein alcali vtgctabilis et dc- 

 purati, nam hcierogenea magis noccnt quam juvant. Berg, ibidem. 



§ Ut CO purillsobtineatur alumen in altera cryftallizaiionc nonnuUis in locis ailditamtnta ufurpantur alcalina, 

 calx et urina. Scilfcct multorum annorum experientii compertum eft, lixivium allquando tantam ct adquirere 

 confiftemiam (quod in officinii pingucfccre dicitur) ut ctcryftalll ygre fcccrnaniur, ct quae prodeunt variis hctt- 

 logcncis irrctit-t; rcpeiiantur. His incommodis alcalinis prajferlim obicem poncre tcntatum fuit, quiim lixivium 

 aciditatc abundarct. Cincris clavetlati ct catx, five ufta five ctu.la, acidum abforbenr, et fi juft.1 adjcntur doli 

 pcrcgrina noxia rc-vcra pracipiiando minuunt, quod, cogniti Uxiviorum indole, S. IX. liiculeiuius patcbit. 

 I'rina tamen nihil cflicit, nifi quatenus alcali volaiili pradiia. Ncgari tamcn non potcft quin novi falcs peregrini 

 jmmifccantur, nimirum alcali vegetabile vitriolatum, vel alii pro divcrfo additnmcnio, fine dubio, fuWatis magia 

 i(iK>cui, fed nihiiominus proalumini vcadendi. Berg. lUid p. 31c.' 



