Ark of Bulrushes

Concise Bible Dictionary:

The little boat or cradle in which Moses was placed by his mother. It was made of bulrushes, or rather paper-reeds or papyrus which grew in the river Nile. It was daubed with slime and with pitch, that is, most probably first covered with wet earth or clay, and then with bitumen (Ex. 2:3,53And when she could not longer hide him, she took for him an ark of bulrushes, and daubed it with slime and with pitch, and put the child therein; and she laid it in the flags by the river's brink. (Exodus 2:3)
5And the daughter of Pharaoh came down to wash herself at the river; and her maidens walked along by the river's side; and when she saw the ark among the flags, she sent her maid to fetch it. (Exodus 2:5)
). Some of the heathen writers speak of the papyrus-woven craft of the Nile. God answered the faith of the parents, and Moses was drawn out of the water to be the savior of His people.
The Nile

From Manners and Customs of the Bible:

1. The precise form of this little “ark” is unknown. It may have been a basket, a boat, or a box. It was made of the leaf of the papyrus, a reedy plant which grew plentifully on the banks of the Nile, and which was used by the Egyptians for cordage, baskets, boats, sails, writing material, and a variety of other purposes; even sometimes for food.
2. The “slime” or bitumen is described in the note on Genesis 11:33And they said one to another, Go to, let us make brick, and burn them throughly. And they had brick for stone, and slime had they for mortar. (Genesis 11:3) (#2). We have here an illustration of the manner of its use. Though melting easily and running freely, when cold it is very brittle; but if mixed with tar it becomes tenacious when set, and makes a firm cement. In preparing the little vessel for the reception of the infant Moses, it is probable that the papyrus leaves were first plaited together, and then coated with a mixture of hot bitumen and tar, which when cold became firm and waterproof.

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