Researching old (like century-old) papers it is common for chemists to describe preparations in terms of parts – e.g., "1 part water, 2 parts sulfuric acid."

Is there a reliable convention on whether this means molar parts or mass parts? I.e., in the above example is the formula 1:2 parts by mass or by molecules?

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    $\begingroup$ There is none. Each time, you have to work your way back to the point where the authors specify which parts they are talking about (or where it becomes clear from the context). $\endgroup$ Sep 18, 2015 at 20:09
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    $\begingroup$ Also, don't forget the possibility of parts by volume. Y'know, to make it that much less ambiguous. $\endgroup$
    – hBy2Py
    Nov 29, 2016 at 12:53


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