Scheele’s paper on Pulvis Algerothi is of considerable scientific interest [12].
Pulvis Algerothi was used as an emetic and laxative and as a precursor for the
preparation of potassium antimonyl tartrate. The common procedure for the
preparation of Pulvis Algerothi was to distill a mixture of antimony (Regulus
antimonii) and mercury(II) chloride (Mercurius corrosivus albus) to afford antimony(III) chloride (Butyrum antimonii), which was hydrolysed with water to form
the desired product:
2Sb þ 3HgCl 2 ! 2SbCl 3 þ 3Hg
SbCl 3 þ H 2 O ! SbOCl þ 2HCl
Scheele noted that this procedure was awkward, expensive and dangerous.
Scheele’s analysis of the problem reveals a deep insight into the chemistry of
antimony, he was, for instance, well aware that antimony occurs in three oxidation
states.
Scheele explained that according to the prevailing theory, antimony had a higher
affinity for hydrochloric acid than mercury, and therefore antimony would attract
hydrochloric acid from mercury(II) chloride. Scheele did not accept this explanation
as he knew that antimony in antimony(III) chloride is in the middle oxidation state
or was “half-calcined” [13] to use Scheele’s words and that hydrochloric acid could
not oxidise (calcine) antimony. He continued: “it is well known that the mercury in
the corrosive sublimate [HgCl 2 ] is not in a reguline form [i.e. in oxidation state 0],
but in the state of a calx [i.e. in a higher oxidation state]”. Scheele correctly
concluded that antimony transferred phlogiston to (i.e. it reduced) mercury(II)
chloride to mercury and the liberated hydrochloric acid united with the oxidised
(calcined) antimony. Scheele concluded that the precursor should be
“half-calcined”, i.e. in oxidation state +III,
5 and finally derived at the following
procedure: antimony(III) sulphide (Antimonum crudum) is mixed with potassium
nitrate (saltpetre) and ignited in an iron mortar. The product is powdered and mixed
with water, sulphuric acid and common salt. This was cheaper than using
hydrochloric acid. The mixture is heated gently under stirring in a sand bath for
12 h. After cooling, the mixture (containing SbCl 3 ) is filtered and mixed with hot
water, which precipitates Pulvis Algerothi.
27.4 A New Method for Preparing Magnesia alba
In 1785, Scheele published a short paper [14] describing an improved method for
the preparation of Magnesia alba, Mg 5 (CO 3 ) 4 (OH) 2 ∙ 5H 2 O, an important substance in eighteenth-century medicine [15]. The standard method was to precipitate
Magnesia alba from a solution of magnesium sulphate (English salt) with
5
“Fully calcined antimony” would have corresponded to antimony in oxidation state +V.
370
27 Scheele’s and Bergman’s Contributions to Pharmaceutical Chemistry
Pulvis Algerothi was used as an emetic and laxative and as a precursor for the
preparation of potassium antimonyl tartrate. The common procedure for the
preparation of Pulvis Algerothi was to distill a mixture of antimony (Regulus
antimonii) and mercury(II) chloride (Mercurius corrosivus albus) to afford antimony(III) chloride (Butyrum antimonii), which was hydrolysed with water to form
the desired product:
2Sb þ 3HgCl 2 ! 2SbCl 3 þ 3Hg
SbCl 3 þ H 2 O ! SbOCl þ 2HCl
Scheele noted that this procedure was awkward, expensive and dangerous.
Scheele’s analysis of the problem reveals a deep insight into the chemistry of
antimony, he was, for instance, well aware that antimony occurs in three oxidation
states.
Scheele explained that according to the prevailing theory, antimony had a higher
affinity for hydrochloric acid than mercury, and therefore antimony would attract
hydrochloric acid from mercury(II) chloride. Scheele did not accept this explanation
as he knew that antimony in antimony(III) chloride is in the middle oxidation state
or was “half-calcined” [13] to use Scheele’s words and that hydrochloric acid could
not oxidise (calcine) antimony. He continued: “it is well known that the mercury in
the corrosive sublimate [HgCl 2 ] is not in a reguline form [i.e. in oxidation state 0],
but in the state of a calx [i.e. in a higher oxidation state]”. Scheele correctly
concluded that antimony transferred phlogiston to (i.e. it reduced) mercury(II)
chloride to mercury and the liberated hydrochloric acid united with the oxidised
(calcined) antimony. Scheele concluded that the precursor should be
“half-calcined”, i.e. in oxidation state +III,
5 and finally derived at the following
procedure: antimony(III) sulphide (Antimonum crudum) is mixed with potassium
nitrate (saltpetre) and ignited in an iron mortar. The product is powdered and mixed
with water, sulphuric acid and common salt. This was cheaper than using
hydrochloric acid. The mixture is heated gently under stirring in a sand bath for
12 h. After cooling, the mixture (containing SbCl 3 ) is filtered and mixed with hot
water, which precipitates Pulvis Algerothi.
27.4 A New Method for Preparing Magnesia alba
In 1785, Scheele published a short paper [14] describing an improved method for
the preparation of Magnesia alba, Mg 5 (CO 3 ) 4 (OH) 2 ∙ 5H 2 O, an important substance in eighteenth-century medicine [15]. The standard method was to precipitate
Magnesia alba from a solution of magnesium sulphate (English salt) with
5
“Fully calcined antimony” would have corresponded to antimony in oxidation state +V.
370
27 Scheele’s and Bergman’s Contributions to Pharmaceutical Chemistry