What time - In the time; or after a time.
They wax warm - Gesenius renders this word (יזרבו yezorebû ) when they became narrow, and this version has been adopted by Noyes. The word occurs nowhere else. Taylor (Concord.) renders it, “to be dissolved by the heat of the sun.” Jerome, fuerint dissipati - “in the time in which they are scattered.” The Septuagint, τακεῖσα Θέρμης γενομένης takeisa thermēs genomenēs - “melting at the approach of heat.” The Chaldee, “In the time in which the generation of the deluge sinned, they were scattered.” Castell says that the word זרב zârab in the Piel, as the word in Chaldee (זרב zerab ) means “to flow”; and also that it has the same signification as צרב tsârab to become warm. In Syriac the word means to be straitened, bound, confined. On the whole, however, the connection seems to require us to understand it as it is rendered in our common translation, as meaning, that when they are exposed to the rays of a burning sun, they evaporate. They pour down from the mountains in torrents, but when they flow into burning sands, or become exposed to the intense action of the sun, they are dried up, and disappear.
They vanish - Margin, “are cut off.” That is, they wander off into the sands of the desert until they are finally lost.
When it is hot - Margin, “in the heat thereof.” When the summer comes, or when the rays of the sun are poured down upon them.
They are consumed - Margin, “extinguished.” They are dried up, and furnish no water for the caravan.