Ordinates, Equiv. Evaporation from and at 212° per Ib. of Combustible

13.60

8

Christie

10.79

10.41

FIG. 74.

DIAGRAM X.

11.43

10.62

.393

.407

.3

.4

.5

.6 .7 .8 Coal per hour per sq. foot of H.S.

FIG. 75.

.9

1.0

25 30 35 40 45 50

Coal per hour per sq. foot of Grate

FIG. 76.

rids itself of some of the impurities in the water, and the dust in the fire gases, to a much greater extent than horizontal surface.

It has been stated that the fire gases carry with them out of the furnace about 1 per cent. of the total weight of the coal burned. With horizontal tubes this flue dust can only be removed by blowing and scraping, while with vertical tubes it is regularly removed by the action of gravitation.

Two elements of the deposit made by the water usually fed to boilers are the mud and the hard, glassy-like scale which will be found on the remotest part of the heating surface. The mud will settle; the hard, glassy scale can be loosened by the judicious use of soda, combined with the expansion and contraction of the metal, and will then also settle.

The action of a horizontal tube, compared with a vertical one, so far as the foregoing elements are concerned, is illustrated by the following diagram (Fig. 80).

The horizontal fire tube collects much flue dust and some scale. The horizontal water tube collects much scale and some flue dust. The vertical water tube, if properly arranged, gets rid of flue dust, mud, and loose scale by gravity.

As the cleaning of the flue dust, mud, etc., from horizontal tubes can only be done at intervals, the inevitable result is that vertical tubes are more economical of fuel than horizontal tubes.

In vertical fire-tube boilers the mud and loose scale settle on the flat tube plate which forms the roof of the furnace. This is the source of great trouble and expense, and is one of the reasons why the vertical fire-tube boiler has not come into general use.

In vertical water-tube boilers with straight tubes, the flue dust settles on the flat horizontal tube plate, forming the top of the mud drum, and it cannot be removed because it is impossible to get access to it.

Although the vertical surface naturally rids itself of flue dust, mud, and loose scale, there still remain the soot and the tough scale, which adhere to all surfaces, whether vertical or horizontal, and which must be removed by mechanical means.

In a vertical fire-tube boiler, to clean the soot from the tubes necessitates the shutting down of the boiler. The man must get on top of the boiler, and either remove the chimney or get into it, and each tube must be cleaned individually at considerable expense of time and steam. In vertical water-tube boilers, in

which the tubes are arranged in circles, it is impossible to brush the soot off the tubes. In vertical water-tube boilers, in which the tubes are arranged in parallel rows, hundreds of tubes can be effectively blown by a simple power apparatus, without opening a door, and in about the same time that it takes to blow one tube in a fire-tube boiler.

When the matter of the tough scale, which adheres even to vertical surfaces, is taken into consideration, it will be seen that the vertical fire-tube boiler is open to the same fatal objection which has been found to horizontal fire-tube boilers, viz.: access to some places is impossible. I was taught the necessity for providing access to every foot of the heating surface for the purpose of cleaning the scale by mechanical means, by a severe experience in Brooklyn, in 1885, with the first water-tube boiler I built. This boiler was not readily accessible for cleaning, and gradually accumulated scale. One night a tube burned out and burst, scalding two men so badly that, although they recovered, their lives were despaired of for a time. This was the only case in which men have been injured by a boiler with which I have been connected. It was a hard and costly lesson, but it

taught me that circulation will not keep a boiler clean even with exceptionally good water, such as Brooklyn had in 1885, and that it is necessary to provide easy access to every foot of the heating surface for the purpose of removing this tough scale, in order that a boiler may be safe, economical, efficient, and durable. There may be an occasional exception, such as the water of the Merrimac River, but I have had no experience with such pure water, and it is rarely met with.

The superiority of vertical over horizontal tubes, and the advantage of convenient access and machine cleaning, were well illustrated by a case in Scotland. A large steel works there gave me an order, in 1894, for a water-tube boiler of 4,370 feet of heating surface, to be installed between rows of Babcocks. The water was very bad, necessitating the stoppage of each Babcock for one day every five weeks for cleaning, and four men were constantly employed cleaning the Babcocks. The large boiler, which I installed, ran far beyond its rated capacity for eighteen months, night and day, without stoppage for cleaning. The mud and the hard, glassy scale were removed regularly by blowing off, by the judicious use of soda, and by washing out with a hose. Although the owners of the boiler wrote me that the tubes near the feed pipe were gradually filling up, I pursued my journeys in Britain and on the Continent, and at the end of eighteen months I cleaned the tubes near the feed pipe in a few hours, and the boiler went to work again for another long period. Some of the tubes in this boiler, which were cleaned without difficulty, had bends amounting to 180° in each. It has been said that scale inside of a bent tube cannot be cleaned, and that boilers constructed of bent tubes have died a natural death and been buried because they could not be cleaned, but the fact is that vertical bent tubes, entering radially into horizontal drums, can be cleaned quicker, by power apparatus, than straight tubes either vertical or horizontal. I have been informed by an eminent member of this Society that in parts of Ohio, where the water is bad, bent tubes, when scaly, are cut out and replaced with new ones. This is unnecessary because vertical bent tubes can be cleaned readily by power apparatus.

I wish here to give a word of caution as to the danger of using water-tube boilers with straight tubes and flat tube plates. It was a boiler of this description, called the Firmenich, which exploded and wrecked a large flour mill, in St. Louis, several years ago. The strains on the tube plates of water-tube boilers are

totally different from those in fire-tube boilers. A little reflection will convince any engineer that flat tube plates in a water-tube boiler, to be safe, must have a stay between each tube, and this is the case in the Heine boiler. Stays in the drums of vertical watertube boilers make them inaccessible for cleaning; therefore I say avoid flat tube plates in water-tube boilers, as they are very dangerous.

There is still another reason why vertical boilers have won for themselves the highest place. In properly constructed vertical boilers the heating surface is further removed from the fire than in horizontal boilers. This is a very important matter, as the volatile hydrocarbons, which form a large percentage of all bituminous coals, require for their proper combustion that there shall be time and space between the grate and the heating surface.

There are two other matters, in addition to the economy of coal, which should be noted in favor of vertical tubes: 1st, the much smaller cost in cleaning; and, 2d, the saving in interest, depreciation, and repairs from the use of fewer boilers, due to the fact that stoppages for cleaning are shorter and less frequent.

Taking the data which Mr. Dean gives in his paper, read at this meeting, an economy of coal of 7 per cent., due to vertical boilers, as shown by Mr. Christie's tests, work out at 55 cents per horse-power year. First-class vertical water-tube boilers can be bought and installed complete, to-day, for less than $5 per indicated horse-power, so that it would pay more than 10 per cent per annum to throw out horizontal boilers and substitute vertical water-tube boilers.

Prof. R. C. Carpenter.-In the paper by Mr. Christie is an extensive collection of results of boiler tests, but I cannot but feel that in its present form the data so laboriously collected will be of little value; it could, however, be made of great value by giving additional information in relation to each test regarding kind of fuel, make of boiler, and authority quoted.

It is also regretted that the diagram of results is not plotted with reference to combustible per square foot of grate, especially for the bituminous coal, instead of coal per square foot of grate. It would seem that such data must have been available, or at least could have been found by calculation, since the results are given as evaporation per pound of combustible instead of per pound of coal. The heating value of coal used in different sections of the country varies more than 50 per cent. for an equal