# Was carbon dioxide also called carbonic acid historically?

I am reading the classic paper by Thomas Andrews, in which he discovered the critical point.

The gas he used in his experiments is called by him 'carbonic acid'. By its critical temperature being 31.1 Celsius, I infer that it is actually 'carbon dioxide'.

Do I get it right?

• No. Carbon dioxide is $CO_2$. Carbonic acid is $H_2CO_3$. – Alexandre Eremenko May 6 '18 at 14:48
• Is it true that chemical symbols should be in roman type, not italic? $\text{CO}_2$ and not $CO_2$ – Gerald Edgar May 7 '18 at 12:30
• @GeraldEdgar in comments we just use the simplest Markdown / LaTeX tools. Don't take them as gospel. – Carl Witthoft May 7 '18 at 12:39
• @Gerald Edgar: probably. But I do not know how to type subscripts without using TeX/ MathJack. – Alexandre Eremenko May 7 '18 at 18:51
• My MathJax idiom is something like C O dollar {} sub 2 dollar, which is terser than something like dollar mathrm{CO}_2 dollar . – kimchi lover May 7 '18 at 21:40

Yes. The Oxford English Dictionary gives instances of the term "Carbonic acid" meaning CO${}_2$ as old as about 1800. By 1900, the term "carbonic acid gas" was in common use for CO${}_2$ (my father called it that, 1950-2000, for instance). More recently it turns out that there is a gaseous phase of H${}_2$CO${}_3$, so "carbonic acid gas" has become an ambiguous term.