Editing Alum (section)

===Modern understanding of the alums===
During the early 1700s, [[Georg Ernst Stahl|G. E. Stahl]] claimed that reacting sulfuric acid with limestone produced a sort of alum.<ref name=Stahl-1703/>{{efn|
CVII.  ''Vitriolum, ''Creta'' præcipitari potest, ut omissa metallica sua substantia, ''aluminosum'' evadat.''
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:[107.  Sulfuric acid {{grey|[and]}} ''chalk'' can {{grey|[form a]}} precipitate, as its liberated metallic substance, ''alum'', escapes.]
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''Ausführliche Betrachtung und zulänglicher Beweiss von den Saltzen, daß diesselbe aus einer zarten Erde, mit Wasser innig verbunden, bestehen''
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:[Detailed treatment and adequate proof of salts, that they consist of a subtile earth intimately bound with water]
:::— G. E. Stahl (1703)<ref name=Stahl-1703/>}}{{efn|Wäysenhaus, [[Halle (region)|Halle]]
''...&nbsp;wie aus Kreide und Vitriole-Spiritu, ein rechter Alaun erwächset:&nbsp;...''
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:[...&nbsp;as from chalk and sulfuric acid, a real alum arises&nbsp;...]
:::— G. E. Stahl (1723)<ref name=Stahl-1723/>}}<ref name=Stahl-1723/> The error was soon corrected by [[Johann Heinrich Pott]] and [[Andreas Sigismund Marggraf]], who showed that the [[Precipitation (chemistry)|precipitate]] obtained when an alkali is poured into a solution of alum, namely [[alumina]], is quite different from [[Lime (mineral)|lime]] and [[chalk]], and is one of the ingredients in common [[clay]].<ref name=Pott-1746-Chym-Untrs/>{{efn|''Concentrirt man hingegen diese solution gelinde, und läßt sie crystallisiren, so schiessen harte und mercklich adstringente und hinter her etwas süßliche crystallen an, die allen Umständen nach in der Haupt-Sach nichts anders sind als ein formaler Alaun. Diese Entdeckung ist in der physicalischen Chymie von Wichtigkeit. Man hat bishero geglaubt, die Grund-Erde des Alauns sey eine in acido Vitrioli solvirte kalckige ... Erde,&nbsp;...''
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:[On the other hand, if one gently concentrates this solution, and lets it crystallize, then there precipitate hard, noticeably astringent crystals with a somewhat sweet aftertaste, which in all circumstances are mainly nothing other than a form of alum. This discovery is of importance to chemistry. One had hitherto believed {{grey|[that]}} the fundamental earth of alum is a calcareous ... earth dissolved in sulfuric {{nobr|acid,&nbsp;...]}}
::: — J. H. Pott (1746)<ref name=Pott-1746-Chym-Untrs/>
}}<ref name=Marggraf-1754/>{{rp|pages=41–66}}

Marggraf also showed that perfect crystals with properties of alum can be obtained by dissolving alumina in [[sulfuric acid]] and adding [[potash]] or [[ammonia]] to the concentrated solution.<ref name=Chisholm-1911/>{{rp|page=766}}<ref name=Marggraf-1754/>{{rp|page=31–40}} In 1767, [[Torbern Bergman]] observed the need for potassium or ammonium sulfates to convert [[aluminium sulfate]] into alum, while sodium or calcium would not work.<ref name=Bergman-1767/>{{efn|
After acknowledging that Marggraf had noticed that potash caused alum to crystallize from a solution of alumina and sulfuric acid, Bergman adds
:''"Notatu quoque dignum est, quod hoc cristallisationis obstaculum alcali volatili aeque tollatur, non vero alkali minerali et calce."''
::[It is significant as well that by {{grey|[use of]}} the volatile alkali (''i.e., ammonia'') this obstacle to crystallization is similarly removed, but not {{grey|[in the cases of]}} mineral alkali]
::(''i.e., sodium carbonate and lime'').
:::— Bergman (1767)<ref name=Bergman-1767/>}}<ref name=Chisholm-1911/>{{rp|page=766}}

The composition of common alum was determined finally by [[Louis Nicolas Vauquelin|Louis Vauquelin]] in 1797. As soon as [[Martin Heinrich Klaproth|Martin Klaproth]] discovered the presence of potassium in [[leucite]] and [[lepidolite]],<ref name=Klaproth-1797/><ref name=Klaproth-1801/>{{efn|"On the contrary, I was surprised in an unexpected manner, by discovering in it another constituent part, consisting of a substance, the existence of which, certainly, no one person would have conjectured within the limits of the mineral kingdom ... This constituent part of leucite ... is no other than ''pot-ash'', which, hitherto, has been thought ''exclusively'' to belong to the ''vegetable kingdom'', and has, on this account, been called ''vegetable alkali''.
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This discovery, which I think of great importance, cannot fail to occasion considerable changes in the systems of natural {{nobr|history, ... ." — [[Martin Heinrich Klaproth|M. H. Klaproth]] (1801)<ref name=Klaproth-1801/>}}
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[[Louis Nicolas Vauquelin|Vauquelin]] demonstrated that common alum is a [[double salt]], composed of sulfuric acid, alumina, and potash.<ref name=Vauquelin-1797/> In the same journal volume, [[Jean-Antoine Chaptal|Chaptal]] published the analysis of four different kinds of alum, namely, Roman alum, Levant alum, British alum, and an alum manufactured by himself,<ref name=Chaptal-1797/> confirming [[Louis Nicolas Vauquelin|Vauquelin]]'s result.<ref name="Chisholm-1911" />