What does the word "pipe" mean in Poe's "The Cask of Amontillado?"

It is significant that Montresor claims to have bought such a large quantity of Amontillado. It seems unlikely that he would have wanted that much of that kind of wine for himself. A  pipe containing 126 gallons would make 500 quarts. More likely Montresor would bottle it and sell it in cases at a good profit--that is, if the Amontillado truly existed. Fortunato is not interested in merely tasting the wine and displaying his conneisseurship. He would like to buy some of that bargain-priced Amontillado himself. But he has to taste it to make sure it is genuine, because Montresor tells him he has doubts.

"I have my doubts," I replied, "and I was silly enough to pay the full Amontillado price without consulting you in the matter. You were not to be found, and I was fearful of losing a bargain."

Note that he says it was a bargain. Fortunato is rich. He could buy a whole shipload of Amontillado and strike an even better bargain. This is why he is so eager to taste Montresor's wine.