The exact chemical composition of potassium and sodium compounds, and the status as chemical element of potassium and sodium, was not known then, and thus Antoine Lavoisier did not include either alkali in his list of chemical elements in 1789.
ðɪ ɛɡzˈækt kˈɛmɪkəl kˌɑːmpəzˈɪʃən ʌv pətˈæsiəm ænd sˈoʊdiəm kˈɑːmpaʊndz, ænd ðə stˈæɾəs æz kˈɛmɪkəl ˈɛlɪmənt ʌv pətˈæsiəm ænd sˈoʊdiəm, wʌz nˌɑːt nˈoʊn ðˈɛn, ænd ðˈʌs ˈæntɔɪn lɐvˈɔɪziɚ dɪdnˌɑːt ɪŋklˈuːd ˈiːðɚɹ ˈælkəlˌaɪ ɪn hɪz lˈɪst ʌv kˈɛmɪkəl ˈɛlɪmənts ɪn wˈʌn θˈaʊzənd sˈɛvənhˈʌndɹɪd ˈeɪɾi nˈaɪn.