Section 22. The chief justice shall receive a salary of $151,239 and each associate justice shall receive a salary of $145,984 and the chief justice and each associate justice shall annually receive from the commonwealth upon the certificate of the chief justice the amount of expenses incurred by each of them in the discharge of his duties. Such justices shall devote their entire time during ordinary business hours to their respective duties and shall not, directly or indirectly, engage in the practice of law.