“Mercury congeals only at seventy-two degrees below the freezing point.”
-40° F, which is also -40° C. This figure is correct, though approximate.
“The proportion stated by Sir H. Davy, in his Chemical Researches, is as 1 to 2.389.”
[ammonia] “consisted of about one part of hydrogen to four parts of nitrogen.... and from the latest and most accurate experiments, the proportions appear to be, one volume of nitrogen gas to three of hydrogen gas”
These and similar calculations involving relative weight and volume make more sense when one knows the elements’ atomic weights. For nitric acid, HNO3, the figures are 1:14:48, giving a proportion closer to 1:3.5. For ammonia, NH3 (not 4), the figures are 14:3.
The first proportion was printed “2,389”. No other decimal numbers occur in the text, but a comma appears once as a thousands separator.
“The oxalic acid, distilled from sorrel, is the highest term of vegetable acidification; for, if more oxygen be added to it, it loses its vegetable nature, and is resolved into carbonic acid and water;”
Oxalic acid = H2C2O4; carbonic acid (carbon dioxide) = CO2. H2C2O4 + O becomes H2O + CO2 + CO2.
Chapter Numbering
The 3rd and 4th editions used the same Conversation (chapter) numbering. The apparent disappearance of XI and XII is the result of changes between the 4th and 5th (present text) editions: