Having described the various methods of fitting up hot-water boilers in England, and have also given a description of a plan in vogue in Canada, I shall now refer to the various methods adopted in the United States, and I will allude first to the "back-log boiler," which has been extensively used in Philadelphia and in other portions of Pennsylvania. It takes its name because, like the large log in the old-fashioned fire-place, it lies across the chimney-breast, behind the ovens, and across the flues.

The flame passes under and back of the boiler, and so up the flues. They are generally bricked in; they last about eight or ten years before burning out. One difficulty experienced is that when any repairs are required, the brick-work must be removed and the range taken out. They do not heat water as rapidly as the ordinary circulating-boiler, but, being cheaper, have been largely used in the city referred to. It will be borne in mind that the tenement-house, as we know it in New York, is there but little known, so that every mechanic can have his house; and even in these humble dwellings they have their bath-tub, and bath-boiler to make hot water, as I have here described. These back-log boilers are made of wrought-iron, the same shape as our circulating-boilers, with cast-iron heads and bottoms. They are usually not galvanized. They have two couplings on one end, one for the cold water to enter and the other for the hot water to pass out. he ordinary wrought-iron circulating-boilers were, I believe, first made and brought into general use also in Philadelphia within the last fifteen years. They have very largely superseded the copper boilers, mainly because in most cities the boiler is supplied from the main direct, and not from a tank. This, as will be seen, subjects them to whatever pressure the water exerts, which in many cases is quite heavy. Take, for instance, a city where the water is distributed by what is known as the "Holly system" - namely, by pumping through the mains. This, under ordinary circumstances, keeps the pressure at about 50 pounds per square inch; but when a fire occurs it is suddenly increased by speeding up the pumps to 150 pounds per square inch. It will be manifest that under such a pressure boilers and all pipes are subjected to a very severe strain; in fact, one which the ordinary copper boilers, as sold in the market, are unable to withstand.

Figure 89.

Copper boilers could, no doubt, be made to stand more than the present so-called "Brooklyn" and 'croton" pressure ones will; but competition during the last twelve years has resulted in bringing these standards down, so that boilers made in conformity thereto will not long remain tight under more than 30 pounds cold-water pressure.

There is no doubt that the water passing through the galvanized-iron boilers will, after a time, be more or less affected by rust, and that the copper boilers, with their interior surfaces well tinned, are more desirable, provided they can be so fitted up as to be durable. This can unquestionably be done, but in doing it the plan of fitting up boilers will have to be materially changed in most of the cities of the United States; in other words, we must adopt the plan in vogue in Boston, which I decidedly prefer, and which I will illustrate further on.

In Figure 89 is shown the usual way of fitting up galvanized-iron or copper circulating-boilers, when supplied direct from the main. A is the cold-water pipe, with a branch to the coupling on top of the boiler, the dotted line C indicating the circulating-tube, which in a copper boiler is made of tinned copper, and has a small hole in it about four inches from the top to admit air, to prevent, under certain conditions, this tube acting as the short leg of a syphon. In galvanized-iron boilers wrought-iron tubes are used; this hole should also be drilled into these tubes for the same reason, but as a rule it is not done by dealers, and many plumbers never think of doing it. The dotted line E indicates the method of running a circulation-pipe, if it is proposed to have one, and D is the hot-water pipe.

The advantages and disadvantages of this system will again be referred to.

It frequently happens that householders complain of an insufficient supply of hot water where the heating-apparatus is arranged as shown at Figure 89. There are numerous reasons why this contingency occurs, many of which have been repeatedly stated in answers to queries in the columns of the Sanitary Engineer, but when the cause is due to the fact that the heating surface of the water-back is not large enough, an arrangement made in this city, which is shown in Figure 90, can be and has been used with advantage.

This, as will be seen, is an auxiliary water-heater, which is placed under the boiler, and also serves the purpose of a stand. It can be used with a range, or separately.

The cut shows the arrangement of the pipes to connect the heater with the boiler, and also the method of connecting with the water-back of the range.

Figure 86 illustrated an English form of boiler that requires a separate fire. In Figures 91 and 92 a boiler is shown for use under simlar circumstances.

The figures give the elevation and section of a conical hot-water boiler made by the same firm that makes the one shown in Figure 90. These are intended for heating water for baptisteries, barber-shops, bathing establishments, laundries, conservatories, and places where a large quantity of hot water is required, and where a range is not needed, or other means for heating water are not provided. As will be seen by the sectional view, the boiler consists of two conical cylinders, one within the other, with a space for water between the two; the inside one forms the fire-chamber, and reaches nearly to the top of the boiler, with an outlet to the smoke-pipe or chimney. There is also a flattened cone connected with the crown of the chamber and extending to within a few inches of the fire, and there connecting at the side of the chamber with a pipe for the passage of the water. The water enters through the lower pipe at the back part of the boiler, and is distributed through the space surrounding the fire-chamber and through the flattened cone, and, as it becomes heated, rises and flows out of the pipe at the top. They are made, I believe, of various sizes, heating from 50 to 400 gallons of water per hour. It will be understood that a tank or reservoir is required. The water in the tank is heated by circulating through the boiler, the two being connected by pipes on the same principal as with a water-back, the boiler, with its independent fire, doing essentially the same duty as the range and water-back, only on a larger scale.