Section 2G. The clerk of the court for Essex county shall, not less than twenty-eight days before the first Mondays of January and May, and the second Monday of September respectively, issue writs of venire facias for forty-five veniremen from whom the court shall select twenty-three grand jurors to serve in said court, who shall serve for each sitting thereof for four months and until another grand jury has been impanelled in their stead.