When the boiling is completed, the brewer again descends to a still lower floor, where we see, besides many engines, pumps and other gear, a large black rectangular tank which is placed directly under, and connected with the boiling-coppers. This is technically called a hop-retainer or hop-back; the former term undoubtedly more intelligible than the latter, and certainly more appropriate because the function of this tank is to check or retain the hops, while the hopped wort, flowing through open valves in the bottom of the coppers, is being rapidly pumped back to the top floor, where an expansive iron receptacle called the cooling-tank, stands ready to receive it. Poor John Barleycorn! In different conditions he has now made this same trip up and down for the fourth time, and yet the end of his journey is still far off. The contrivance which effects the retention of the hops consists of a perforated false bottom within the hop-back, or, in other words, of a sieve equally as large as the iron tank into which it is fitted, and so fixed as to leave between it and the real bottom of the vessel a sufficient space for the reception of the wort. At this stage, the head-brewer thinks of but two things, namely, to send his wort to the cooling-tank as rapidly as possible and to have it reach its destination clear and brilliant. For the latter purpose he allows the wort to settle in the hop-back for about twenty minutes; this done, he adjusts the pumps, sets them in motion, and then ascends to the top floor to watch the steaming liquid, as it issues from the pipe and, with a sound between a hiss and a roar, rushes into the tank. If we wish to form an idea of the shape and dimensions of this cooling-tank, we must do it now, for in a few moments, as the hot liquid accumulates, a dense cloud of steam, fraught with the enlivening aroma of the hops, begins to fill the immense room, rendering everything indistinct, except when a particularly strong gust of wind rushes through the wide openings in the lattice-work of the windows and for a moment lifts the vaporous veil. The shape of this vessel is that of a gigantic rectangular pan; its depth is three feet; its lateral dimensions are 30 x 42 feet; its capacity equals that of two of the three boiling-coppers, each one of which holds three hundred and seventy-five barrels.