Carbohydrate Digestion 1. Label 6 clean test tubes as follows: 1L, 2L, 3L, 1B, 2B, 3B. Also, add some marks for your lab group. The number indicates the sample condition, and the “L” and “B” indicate which test is being performed. The “L” tubes will be used for the Lugol’s test, the “B” tubes will be used for the Benedict’s test.