For analysis of the dissolved substances, the water samples were evaporated over
red-hot charcoal in a soapstone kettle with a wooden lid. To illustrate the procedure,
the analysis of bitter water is taken as an example here: as carbon dioxide was lost,
any dissolved calcium carbonate precipitated first. This was filtered off and
examined: it gave calcium sulphate (gypsum) with sulphuric acid. The evaporation
of the water was continued, and the next salt to precipitate was calcium sulphate
(gypsum) which was identified by its property to give calcium carbonate (lime) and
potassium sulphate (Tartarus vitriolatus) with potassium carbonate (Alkali vegetabile). After filtration, the evaporation was continued, whereupon magnesium
sulphate (bitter salt) crystallised. Reaction with calcium hydroxide solution (lime
water) revealed its identity and excluded confusion with sodium sulphate (Glauber’s salt): the presence of magnesium gave a white precipitate of magnesium
hydroxide. Treatment of the crystallised salt with sulphuric acid revealed the
presence of chloride (Bergman wrote hydrochloric acid, but he did not mean free
acid) since liberated hydrogen chloride gives white fog in moist air.
4
The next paper describing water analysis is a paper which appeared in the first
quarter of 1777. Linnæus’ student Anders Sparrman (1748–1820) had collected
seawater from a depth of about 107 m (60 famnar). Where Sparrman collected the
samples is not told, but Sparrman had participated in James Cook’s second voyage
1772–1775, and after spending some time in southern Africa, he left Cape Town in
April 1776 [26]. The samples were presented to Bergman in October 1776, but
other duties prevented Bergman from analysing the samples until December the
same year [27].
In this paper, Bergman used several chemical reagents to analyse the samples.
The water did not change the colour of litmus tincture (an acid-base indicator;
seawater is only mildly basic with a pH of about 8); it gave a precipitate with
barium chloride solution (“solution of heavy earth in hydrochloric acid”) indicating
the presence of sulphate: “this is, of all known tests, the most reliable way of
revealing vitriolic acid [sulphuric acid], even when its amount is so small, that it is
undetectable by other means”. This is the first mentioning of barium chloride as a
reagent for sulphate. Oxalic acid (acid of sugar) also gave a precipitate with the
water, indicating the presence of calcium (lime); alkali carbonate (Alkali fixum)
precipitated magnesium (magnesia) and potassium hexacyanoferrate (lye of blood)
revealed traces of iron.
To perform a quantitative analysis, Bergman evaporated 2.6 L (1 kanna) of
water to dryness, yielding 113 g (8.46 lod) of residue. The residue was extracted
with ethanol (Spiritus vini rectificatissimus), which dissolved magnesium chloride.
Extraction with a small amount of boiling water revealed the presence of magnesium sulphate (bitter salt). The sodium chloride
5 was extracted with the minimum
amount of water leaving calcium sulphate (gypsum) undissolved. Bergman
obtained 86.2 g of sodium chloride, 23.5 g of magnesium chloride and 2.79 g of
4
Bergman could have used a glass rod dipped in aqueous ammonia, which give a characteristic
white smoke of ammonium chloride.
5
Called koksalt in Swedish, meaning “cooking salt”.
316
23 Bergman as an Analytical Chemist
red-hot charcoal in a soapstone kettle with a wooden lid. To illustrate the procedure,
the analysis of bitter water is taken as an example here: as carbon dioxide was lost,
any dissolved calcium carbonate precipitated first. This was filtered off and
examined: it gave calcium sulphate (gypsum) with sulphuric acid. The evaporation
of the water was continued, and the next salt to precipitate was calcium sulphate
(gypsum) which was identified by its property to give calcium carbonate (lime) and
potassium sulphate (Tartarus vitriolatus) with potassium carbonate (Alkali vegetabile). After filtration, the evaporation was continued, whereupon magnesium
sulphate (bitter salt) crystallised. Reaction with calcium hydroxide solution (lime
water) revealed its identity and excluded confusion with sodium sulphate (Glauber’s salt): the presence of magnesium gave a white precipitate of magnesium
hydroxide. Treatment of the crystallised salt with sulphuric acid revealed the
presence of chloride (Bergman wrote hydrochloric acid, but he did not mean free
acid) since liberated hydrogen chloride gives white fog in moist air.
4
The next paper describing water analysis is a paper which appeared in the first
quarter of 1777. Linnæus’ student Anders Sparrman (1748–1820) had collected
seawater from a depth of about 107 m (60 famnar). Where Sparrman collected the
samples is not told, but Sparrman had participated in James Cook’s second voyage
1772–1775, and after spending some time in southern Africa, he left Cape Town in
April 1776 [26]. The samples were presented to Bergman in October 1776, but
other duties prevented Bergman from analysing the samples until December the
same year [27].
In this paper, Bergman used several chemical reagents to analyse the samples.
The water did not change the colour of litmus tincture (an acid-base indicator;
seawater is only mildly basic with a pH of about 8); it gave a precipitate with
barium chloride solution (“solution of heavy earth in hydrochloric acid”) indicating
the presence of sulphate: “this is, of all known tests, the most reliable way of
revealing vitriolic acid [sulphuric acid], even when its amount is so small, that it is
undetectable by other means”. This is the first mentioning of barium chloride as a
reagent for sulphate. Oxalic acid (acid of sugar) also gave a precipitate with the
water, indicating the presence of calcium (lime); alkali carbonate (Alkali fixum)
precipitated magnesium (magnesia) and potassium hexacyanoferrate (lye of blood)
revealed traces of iron.
To perform a quantitative analysis, Bergman evaporated 2.6 L (1 kanna) of
water to dryness, yielding 113 g (8.46 lod) of residue. The residue was extracted
with ethanol (Spiritus vini rectificatissimus), which dissolved magnesium chloride.
Extraction with a small amount of boiling water revealed the presence of magnesium sulphate (bitter salt). The sodium chloride
5 was extracted with the minimum
amount of water leaving calcium sulphate (gypsum) undissolved. Bergman
obtained 86.2 g of sodium chloride, 23.5 g of magnesium chloride and 2.79 g of
4
Bergman could have used a glass rod dipped in aqueous ammonia, which give a characteristic
white smoke of ammonium chloride.
5
Called koksalt in Swedish, meaning “cooking salt”.
316
23 Bergman as an Analytical Chemist