there is to get water. A couple of quarts of unslaked lime put in will help matters; or a piece of bluestone (sulphate of copper, blue vitriol, which may be had at almost any local telegraph office) will aid if put in the hose back of the screen, if there has been no lime or other alkali used.

Q. Why should the throttle be closed slowly, in case of foaming?

A. To keep the water from dropping suddenly below the crown-sheet in case there was an insufficient quantity.

Q. Why open the surface-cock in case of foaming?

A. Because foaming is usually caused by grease, which will be floating on the water and may be blown off by the surface-blow.

Q. Why is lime put in the tank in case of foaming by reason of greasy water?

A. It neutralizes the grease.

A. A hard deposit left on sheets and tubes from water which contains mineral substances in solution or in suspension.

Q. What are its usual constituents?

A. Lime is the most common, in some of its compounds, as carbonate or sulphate; magnesia and iron are also found, as is ordinary clay.

Q. What are preventives of scale?

A. (1) The choice of water having therein no mineral substances that will be left behind in the boiler when the water has been turned into steam; (2) filtration of the water, to remove substances which are only mechanically contained therein; (3) chemical treatment of the water to make it deposit the mineral substances before it reaches the boiler; 4, chemical treatment simultaneously with its supply to the boiler.

Q. Where must the second and the third preventives be resorted to?

A. In the station tank or before the water reaches it. Q. What are resorted to to remove scale once it has formed in the boiler?

A. Petroleum, and various chemicals which exert a loosening effect on the scale already deposited.

Q. Will black oil soften all kinds of scale?

A. No.

Q. Would lard oil or valve oil help?

A. No; it would cause foaming and not affect the scale.

Q. How is mud deposit prevented?

A. (1) By filtering; (2) by using pure water; or (3) by frequent blowing off, hot.

Q. What can you say as to the influence of scale in heat transmission in locomotive boilers?

A. Tests go to show that conductivity is diminished from two to 10 per cent by scale and being from 0.02 to 0.085 inch thick.

Q. How would you rate the quality of feed water according to the contents of incrusting solids?

A. I would say that for calcium carbonate, magnesium carbonate, or magnesium chloride, only 8 grains per U. S. gallon would be very good; 20 to 30 bad; over 30, very bad. For sulphate of calcium and magnesium only onefourth as much would be permissible for the same rating. Q. What materials cause incrustation?

A. Mud, soluble salts, bicarbonates, organic matter, lime sulphate.

Q. What causes corrosion?

A. Animal fats and other organic matter, magnesium chloride or sulphate, sugar, acids; either CO, or oxygen in solution.

Q. What feed water impurities cause priming?

A. Sewage, alkalies, sodium carbonate, in large quantities.

Q. Is there any one "boiler compound" that is good for all kinds of bad feed water?

A. No. Some will work well with one water and injure boilers using water obtained a hundred miles away on the same road.

Q. How can you classify boiler compounds?

A. Into those causing a loose deposit, readily removed, those enveloping the deposited particles with a coating that prevents their agglomerating, and those dissolving or disintegrating the scale-forming substances.

Q. What is the effect of using crude oil as a scale preventer?

A. It makes a tough scale that causes bagging.

MUD-DRUM AND HAND-HOLES

Q. What provision is necessary where the water is very impure?

A. A mud-drum-a wrought-iron cylinder below the boiler, usually at the front end, and having a blow-off cock and a removable cast-iron bottom cover. There being in this drum but little water-circulation, most of the mud and scale collects there, instead of being burned on the sheets of the main shell.

Q. How may hard mud and scale be removed?

A. Either (1) through oval hand-holes in the corners of the fire-box, near the bottom, and closed with two plates, one inside and the other outside, connected and fastened with a bolt, or (2) through holes in which are screwed mud-plugs. After as much as possible has been scraped out through these holes, a hose may be inserted and a strong stream of water used to slush out other material not within reach of scrapers.

CHAPTER XXXVII

ESSENTIALS OF A LOCOMOTIVE BOILER

Q. What are the essentials of a good locomotive boiler? A. (1) Reliability and mechanical maintenance-that is, freedom from cracked sheets, leaky seams and flues, leaky and broken stay-bolts.

(2) Continuous development of maximum horse-power within the capacity and endurance of the ordinary fire

man.

(3) An efficiency as near as possible to that of the best stationary and modern boilers.

Q. On what do reliability and low cost of maintenance depend?

A. Principally on freedom of circulation around the fire-box.

Q. What elements go to facilitate such circulation? A. Depth of box and width of water legs.

Q. Should depth be obtained by depth of throat sheet, or by raising the crown sheet?

A. By depth of throat sheet.

Q. Is the ordinary fire-box calculated to withstand the heat of perfect circulation?

A. No; but the better the circulation the less the trouble with the fire-box.