Peel the cucumbers, cut lengthwise in four, remove the seeds and cut in thin slices, 3½ inches long. Boil in a little salted water for 10 minutes. Drain, but keep the water in which the cucumbers were boiled. Melt 1 oz. of butter in a saucepan, put in the cucumbers, sprinkle with 2 teaspoons of flour, mix well, without browning, then add gradually a little more than a gill of the water in which the cucumbers were boiled, and 3 tablespoons of vinegar. Simmer for 10 minutes.