Rashi on Exodus 9:8/רש"י על שמות ט׳:ח׳

1מלא חפניכם HANDFULS (more lit., as much as will fill your fists), old French joincheiz; Engl, double-handfuls.

2פיח הכבשן SOOT OF THE FURNACE — the word פיח denotes a thing which is blown away (נפוח) from coals that have become extinguished after being burnt in a furnace; in old French oulvis.

3פיח is derived from a root that signifies blowing, and it so called because the wind blows it about and scatters it abroad.

4וזרקו משה AND LET MOSES THREW IT — Since anything which is thrown with force must be thrown with one hand only, there were here several miracles: one, that Moses’ closed fingers (קמץ) held as much as would fill his two fists and those of Aaron, and another, that this dust spread itself over the entire land of Egypt (Midrash Tanchuma, Vaera 14; Exodus Rabbah 11:8).