36. Vim li cas nws thiaj li yuav tsum tau tsau cov kav hlau hauv dej kub rau ib ntus ua ntej ntxuav cov kua qaub hauv qee qhov haujlwm?

Ua ntej ntxuav cov kua qaub, cov kav hlau yuav tsum tau preheated hauv dej kub (25-50 degree) rau 1-3 feeb ua ntej cov txheej txheem pib. Qhov kev xyaum no muaj ntau yam txiaj ntsig: (1) Nws tshem tawm cov ntaub ntawv hlau, cov khoom paug, thiab cov roj me me los ntawm cov yeeb nkab tsis muaj nkalized, thaum tseem txhim kho kev ua haujlwm nruab nrab rau alkalized blanks; (2) Preheating accelerates acid ntxuav; (3) Nws txo cov cua sov ncaj qha ntawm cov kua qaub, ua kom nws cov nyhuv dilution ntev; (4) Cov tshuaj tseem huv dua, ua kom cov kua qaub ntxuav zoo dua; (5) Nws txuag kwv yees li 2-3% ntawm acid noj.