The Steamer's Chimney

The atroller along the wharfs who should see rising from the smokestack of a big steamer a sniaü and at tbe start perfectly defined column of smoke whioh seemed to come from a small smokepipe within the big one might wonder if the great smokestack was filled with smaller stacks, one for each boiler. As a matter of fact it is not so filled, but tbere is within it a smaller smoke pipe oalled the donkey stack, which is the obimney for the boiler of tbe donkey engine, which is used when the vessel is ia port in boisting cargo in and out. It 18 from this pipe that the small column of smoke is seen to issue. The donkey stack is placed sometimes against the forward inner side of tbe big stack, sometimes against the after inner side. It may be a complete pipe, or it may be formed of iron in the shape of half apipe, with -ñaages riveted to the inain pipe. If a single one of the large boilers were used, as it might be when the ship is in port, it might be connected with the donkey stack, but in tbeir regular and common arrangement and use the uptakes of all these boilers run into the great chimney, whose whole interior is open, exoept for the bracos running aoross it to strengthen and support it. The chimneys of all large steamships, however, and of many other steam vessels as well are built doublé, with an inner and an outer shell, with a space between varying according to the size of the vessel. It may be from five to ten inches. The primary purpose of tbia ofaamber around tbe smokestack is to afïord ventilation for the engine room and the stokehole. In at least one modern passenger ship ventilating pipea from the passenger quarters have been oarried to these chambers. Incidentally the space between the shells helps to keep the stack sightly, for thus constructed the "chimney is cooler on the outside than it would otherwise be, and