1. While the terms of a written contract cannot be varied by a contemporaneous parol agreement, yet it is permissible to show the existence of a custom of the trade or business, not at variance with such terms, concerning which the contract was made, which is of such universal practice as to justify the conclusion that the custom by implication became a part of the contract. Branch v. Palmer, 65 Ga. 210 (1).

2. Where a written memorandum of sale between two dealers in certain commodities contains the following provisions as respects the delivery of the commodity sold: “ Shipment March ” and “ Shipment April,” it is permissible to explain the meaning of these expressions by showing the existence of a custom or usage among the trade or dealers of such commodities that shipments of commodities when sold on future delivery are not necessarily to be actually made at the time designated in the written memorandum of sale unless delivery is at the time tendered by the seller or demand is made by the buyer, and that where no such tender or demand is made, the time of the delivery is automatically extended from month to month until a tender is made by the seller or a demand is made by the buyer. Such custom does not change, vary or contradict the terms of the contract as respects delivery, but adds a provision, perfectly consistent with the terms of the contract, to the effect that the deliveries contracted for are only to be made upon a tender by the seller or a demand by the buyer, and that in the absence of such tender or demand, the contract is automatically renewed or extended for a month.

3. An agreement between the seller and the buyer to extend the time for the performance of such a contract, “providing the United States Rood Administration would allow it,” it not appearing that the United States Rood Administration did allow it, was void for uncertainty; and it was therefore proper, on special demurrer, to strike paragraph 3 of the amendment to the petition.

4. The petition as amended, with paragraph 3 of the amendment stricken, set out a cause of action, and, not being subject to the other special demurrers interposed, was improperly dismissed on general demurrer.

Judgment reversed.