Historically, it was these atomic weights of elements (in comparison to hydrogen) that were the quantities measurable by chemists in the 19th century.
hɪstˈɔːɹɪkli, ɪt wʌz ðiːz ɐtˈɑːmɪk wˈeɪts ʌv ˈɛlɪmənts ɪn kəmpˈæɹɪsən tə hˈaɪdɹədʒən ðæt wɜː ðə kwˈɔntᵻɾiz mˈɛʒɚɹəbəl baɪ kˈɛmɪsts ɪnðə nˈaɪntiːnθ sˈɛntʃɚɹi.