54' On the different EffeBs of the Alkalis. 



unfit for the produ£l:ion of alum. Not to mention the few fpcies of alum, which I have 

 examined, I (hould not choofe to draw fuch an inference from the refults I did obtain 

 from them. 



SyntJjetical experiments, on the contrary, I am perfuaded, ought to decide in this cafe. 

 And by thefe, (although Marggraf mentions, in a general way only, the pot-afh as a 

 neceflary requifite to the generation of fulphate of alumine, without excluding the foda) 

 \ have until the prefent moment been convinced, that the combination of foda witi* 

 fulphuric acid and argil does not yield any alum-, I mean that very fait, which is known by 

 that name ; but that it is generated by the addition of pot-afh. 



I employed, in my experiments, native foda (natrum) from Hungary, purified in a 

 high degree. It was this purity that induced me to inftitute thofe experiments. And to 

 aflure myfelf that no portion of pot-afh did interfere, I have precipitated the argil from 

 Roman alum, nijt by means of pot-afh, but by foda. If, therefore, fomewhat of the 

 neutral fulphate, generated by the precipitation, had remained in the earth after it was 

 edulcoratedj it muft necefTarily have been fulphate of foda. 



The precipitated alumine was then properly waflied ; and I thought it needlefs to 

 free it, according to Richter, from the adhering fulphuric acid, the prefence of which was 

 not detrimental in this inftance. I then difTolved it in purified fulphuric acid, in excefs, 

 fo that the folution reddened litmus-paper dipped in it. As I have already obferved, the 

 due proportion of the earth to the acid is found of itfelf, by permitting the acid, moderately 

 diluted, to difTolve as much of the earth as it can iii a low temperature. "When I after- 

 wards added to the filtered folution fucceffive portions of difTolved carbonate of foda, till 

 part of the alumine itfelf began to precipitate, I filtered the folution once more, and began 

 to attempt the cryflallization of the fait, by gradually repeated evaporation and alternate 

 cooling. 



But in none of thefe inflances did I obtain alum ; but rather a very filuble fait, altogether 

 different in Its form. This combination is of fo eafy folution, that I might at firft have 

 repeatedly fufpe£ted an accidental tranfpofition of my evaporating difhes, if I had not been 

 fure of the contrary, by the fmall quantity of the rcfidual liquor, and its refufing to ^ 

 cryftallize. That great folubility agrees very well with that of Glauber's fait (fulphate of foda) 

 as vke verfd., the difficult folution of alum correfponds with that fulphate of pot-afh. When, 

 in one of my experiments, I added juft fo much of foda, that the lixivium began to acquire 

 a permanent cloudiiiefs (owing to the argillaceous particles firft precipitated, and which arc 

 redifTolved by the redundant acid, if the fluid be agitated, and thus the earthy particles be 

 brought into contaft * with its not yet alkalized part), there refulted from its farther 

 evaporation and cooling fome minute, fingle, (hort needled crytlals, refembling thofe of 

 ^gypfum. Thefe, however, merely contained aluminous, and no calcareous earth ; for 

 they readily difTolved in water } the oxalic acid precipitated nothing from their folution ; pure 



• The earthy particles newly precipitated are, in general, more foluble, than thofe of a longer {landing and 

 deficcated j becaufe the former are fubtilely divided, and moiftened through the whole of theii' mafs. 



4 (cauflic) 



