Table 10.-CALORIFIC VALUES OF VARIOUS OILS.-Continued.

content can be determined in the bomb calorimeter after the calorific value has been determined. The calorimeter is opened by gradually allowing the pressure to diminish and the bomb is carefully and thoroughly washed out with distilled water. The pan is placed in the beaker with the washings and about 10 cc. of hydrochloric acid is added. The contents of the beaker are treated with bromine, heated to boiling temperature for about 10 minutes, filtered and washed and the sulphur in the filtrate precipitated with 10 cc. of barium chloride solution. The precipitated barium sulphate is filtered, washed and weighed in the usual manner. The weight of the barium sulphate X 13,733 and divided by oil.

Fuel oil in this country is purchased by volume and not by weight. Table 10 shows that a gallon of oil of high specific gravity has a higher calorific value than a gallon of oil of low

specific gravity. This fact should be remembered by users of oil fuel, because in buying fuel calorific value is sought. Individual conditions and requirements at the points of consumption influence to a large degree the specifications for viscosity, flash point and sulphur content. Definite specifications can be drawn for a fuel oil which will meet practically all requirements, but it can readily be seen that such specifications will exclude much of the fuel oil now available, and for most purposes the requirements need not be severe. Hence, it is advised that in purchasing fuel oil the individual requirements be studied, and that as lenient specifications as possible be written, which will insure an oil that will be satisfactory for the conditions for which it is intended.

CHAPTER III

COMPARISON OF COAL AND FUEL OIL

The term "Coal" as applied to fuel is very loosely used. The word is applied to a variety of substances ranging from turf through peat, lignite, semi-bituminous and bituminous coals to anthracite. It is obvious that no comparison can be drawn. between coal and any other fuel unless the specifications of the coal are stated. The value of the chemical analysis of a sample of a given coal to an engineer, power-plant superintendent, or coal dealer, is a matter that has given rise to much discussion. The general weight of opinion seems to be that an analysis is often of the highest value, and that the time and labor involved in making it are well spent. However, it is clear that analyses are of greater value to some engineers or users of coal than to others; and that, at the present time, they cannot entirely supplant in all cases the information to be obtained from carefully conducted tests in boiler furnaces but should supplement such information, when the latter is obtainable.

In the testing of coals in the Government service the chief difficulties in the way of accepting or rejecting untried coals on the basis of chemical analyses alone have proved to be as follows:

(1) An ordinary analysis of a coal shows the percentage of ash, but does not indicate the extent to which this ash may fuse or slag on the grate bars of the furnace, and thus seriously interfere with the rate and completeness of the combustion. Though progress has been made toward the determination of the liability to clinker, through a study of the composition of the ash, the results obtained are not as yet altogether satisfactory.

(2) There seems to be a variability in the heating value of the volatile matter in the coal, which is not clearly indicated by the percentage of the volatile matter, as determined either by the usual methods, or by the ordinary calorimetric determinations.

(3) The caking of the surface coal in the fire box appears to interfere with the draft, and hence, with the rate and completeness of the combustion, and, therefore, impairs the fuel value of the coal to a degree that is not ordinarily indicated by chemical analyses.

For all practical purposes the coal produced in the United States may be divided into three classes, anthracite, bituminous and lignite. The great bulk of the country's coal supply, however, is bituminous or soft coal. Table 11 shows the production of coal in recent years in the United States.

Bituminous is the chief steam coal and when comparisons are made between coal and fuel oil, bituminous coal is used as a basis. Bituminous coal deposits are almost always underlain by fire clay and almost always are overlain by a stratum of shale. The fire clay is the residuum of the original soil in which grew the