Since the apothecary had used twice as much alcohol as water, the total ounces of alcohol and water together must be divisible by 3. The total capacity of all 6 flasks is 137 ounces, a numbeer which is 2 more than a multiple of 3. Because the apothecary left one flask empty, it is obvious that this flask must have a capacity in ounces which is 2 more than a multiple of 3. The only flask which meets this requirement is the one with a capacity of 23 ounces. This flask must have been the one left empty. The remainder, which have a combined capacity of 114 ounces, were filled. One-third of this total, 38 ounces, was water. The 16 and 22 ounce flasks must therefore have been used for water and the 18,24,and 34 ounce flasks used for alcohol.