Unless otherwise stated, stock solutions and buffers should be prepared and made up with distilled water free from carbon dioxide. Standard reagents should be used. The strength of solutions made up with reagents of doubtful purity or degree of hydration must be checked by titration. The amounts x and y of the stock solutions required to yield a desired pH value are given in the table on pages 364 and 365. In the table below, the buffers are arranged in the alphabetical order of their chemical names.