is ground repeatedly with a muller and bucking board until the whole will pass through a 100-mesh sieve. The pulverizing and sifting thoroughly mixes the sample, which is put into the heater for one hour at a temperature of 100 degrees cent. The heater consists of a copper oven surrounded by a water jacket, in which the water is kept at a boiling temperature by a bunsen burner. The coal, now dried out, is ready for analysis. Sulphur, ash and British thermal units are the constituents usually determined-although moisture and volatile combustible matter are sometimes required for boiler and stoker tests.

Sulphur determination. For the sulphur, 0.5 gram of the dry sample is weighed. Two determinations are carried on simultaneously on each sample, in order to have a check on the results. The 0.5 gram of coal is put into a 20-gram platinum crucible halffilled with Eschka mixture, then stirred together, covered with a little more of the mixture and placed over a bunsen flame turned very low for fifteen minutes. Eschka mixture consists of two parts (by weight) of calcined magnesium oxide, (MgO) and one part (by weight) of dried sodium carbonate, (Na,CO,). At the end of 15 minutes the flame is gradually turned up to full power, and the mixture heated for 45 minutes, meanwhile being stirred several times. After the whole has been fused and the coal completely burned out, the contents are turned into a clean beaker, that part of the fusion adhering to the crucible being washed out by means of distilled water and a rubber-tipped stirring rod. 50 c.c. of distilled water are added to the beaker, the whole allowed to boil for a minute on the hot plate, then filtered through a single filter (Munktell 9 c.m.), the precipitate washed with distilled water, 15 c.c. of 1 to 1 hydrochloric acid (HCl) of specific gram, 1.19 added to the filtrate, the solution boiled for a minute and stirred, then 10 c.c. of saturated barium chloride solution (Ba Cl2) added, and the resulting precipitate of barium sulphate (Ba SO,) allowed to settle for two hours or longer, while the beaker rests on the hot plate. When settled, the precipitate is filtered off, (using double filter papers), and washed three times with hot distilled water. The filters are then folded around the precipitate, both placed in a clean platinum crucible, and heated over the bunsen flame until burned out. This takes about half an hour. From the weight of precipitate found is subtracted the weight of Ba SO, obtained as the average of two or three blanks previously run on the Eschka mixture. The corrected weight of sulphate is doubled, (as but 0.5 gram of sample was taken), multiplied by 0.1373-the sulphur factor

and then by 100 to obtain the percentage of sulphur in the coal sample. A sulphur table for half-gram weights is then furnished for reference, thus saving time in figuring results. With six burners and six crucibles at hand, six determinations on three samples of coal are carried on at one time.

Ash determination. When the fused mass in the foregoing sulphur determination has been removed from the crucible, the latter is thoroughly washed out, and in it is placed a gram of the dried coal, accurately weighed for the ash determination. This consists in merely allowing the coal to completely burn out over a full bunsen flame. Sometimes the sample is heated to constant weight, but if burned for two or three hours with frequent and careful stirring, the extra weighing is unnecessary. From the weight of residue found, the percentage of ash in the sample is calculated in the usual way. A half-gram of sample may be used instead of the whole gram, though any error is doubled in this way. Two determinations are made at a time on one sample, and they should check within 0.2 per cent.

While the samples are being heated in the crucibles for sulphur and ash, the B. t. u. determinations are made.

British thermal unit determination. This is accomplished with. a Parr calorimeter, which measures the rise in temperature of 2 liters of distilled water, due to the heat absorbed from the combustion of a fixed amount of coal sample with an oxydizing agent. This combustion takes place in a metal bomb, which is immersed in the water, and caused to rotate at about 100 rev. per min. by a small motor. The coal and oxydizing agent are made to combine by passing a current from a 40-ampere-hour storage battery, giving 6 volts, through an electric fuse in the bomb mixture. The fuse wire is of german silver, No. 36, which melts on passage of the current and starts combustion of the coal. The water used in the calorimeter for the heat absorption is protected from outside heat influences by two fibre tubs with air spaces between.

To determine the heat units in a sample of coal, the bomb is first taken apart, all the parts washed and thoroughly dried, and the fuse-wire fastened to the inside terminals in the form of a loop. 0.5 gram of potassium chlorate (K C1 0,) and 0.5 gram of coal sample are weighed and placed in the bomb. To this is added a measure (10 grams) of dry sodium peroxide (Na, O2). The bomb is now put together, screwed tight with a wrench, well shaken, the water veins adjusted, then immersed in the 2 liters of water, and made to rotate slowly to secure

uniform temperature by the circulation of the water. After about three minutes, the temperature of the water is read from a Fahrenheit scale thermometer inserted through the cover of the calorimeter. The thermometer is calibrated in twentieths of degrees, but the readings are estimated, with the aid of a magnifying glass, to hundredths. After the mercury column has become stationary, the charge in the bomb is exploded, and the thermometer carefully watched, as the mercury rises, until the maximum temperature is reached. The difference between the first reading of the thermometer and the last reading is the rise due to the heat absorbed by the water.

A rise of 0.014 degrees fahr. is due to the heat of the fuse wire used, and a further rise of 0.171 degrees fahr. is caused by the accelerator (K C1 O1). The sum of these two (0.185) is subtracted from the total rise in degrees, and the remainder is multipled by 3117 to obtain the number of heat units in the sample. The number of heat units is the number of grams or pounds of water that 1 gram or 1 lb., respectively, of coal sample during combustion, will cause to rise 1 degree fahr. in temperature.

The above factor, 3117, is obtained in this way: the 2000 c.c. of distilled water used in the calorimeter weighs 2000 grams; the metal bomb and metal containing-cylinder and pivot together are the equivalent of 135 grams of water on the basis of heat absorption. 2000 grams plus 135 grams gives 2135 grams. This number multiplied by the rise in degrees would give the number of gram calories in fahr. degrees given off when 0.5 gram of coal was burned. Therefore, twice this amount represents the calories of heat from 1 gram of coal. It has been experimentally determined that when coal, K C1 O,, and Na, O2 are exploded, only 73 per cent of the heat evolved is due to the combustion of the coal. 2135 X 2 X 0.73 3117, which represents the number of gram calories due to a rise of 1 degree.

=

2

After each explosion, the bomb is washed out, dried, and wired for the next charge. The 2 liters of water used should be about 4 degrees lower than the temperature of the room, and fresh distilled water is used for each explosion. Two determinations for heat units are always made on each sample, and should agree closely. If the rise in temperature in one case varies more than 0.02 of a degree with the rise on another explosion of the same sample, (corresponding with 62 heat units) then successive determinations. are made on this coal until a check or a good average is obtained. A calorific table does away with the calculation and results are obtained directly.

Moisture determination. To find the moisture content the coal in question is first air-dried, a gram of it is weighed, placed in the heater at 104 degrees cent. for one hour and weighed again. The loss in weight divided by the weight of air-dried coal gives the percentage of moisture.

Volatile combustible matter determination. For finding the percentage of volatile combustible matter in coal, a 1 gram sample is placed in a clean weighed platinum crucible, the cover is put on tightly, and the coal heated over the strongest heat of a bunsen burner for three and one-half minutes. At the end of this time the bunsen flame is removed and a blast lamp put under the crucible, care being taken to have a flame below the crucible while making the change, so the contents will not cool. The coal is heated by the blast lamp for three and one-half minutes more, the crucible is allowed to cool in a desiccator and weighed. From the loss in weight from heating, the weight of mois ture found is subtracted, and the difference divided by the weight of the sample taken to find the percentage of volatile combustible matter. This difference also contains one-half the sulphur, and this value, found in another determination, is subtracted, leaving the per cent of volatile combustible matter.

Fixed carbon determination. Remove the cover and burn off the remaining carbon over a bunsen burner until nothing remains but the ash-the loss is fixed carbon with the remainder of the sulphur.

Coke and ashes are analyzed in much the same way that coal is, except that tests for sulphur and moisture are not required. In determining the heat units, however, it is difficult to get an explosion with the ordinary chemical, so the use of benzoic acid is resorted to. 0.5 gram of K C1 03, 0.25 gram of coke or ash sample, 0.25 gram of benzoic acid (CH, COOH), and 10 grams of Na,O, are used for each charge. A correction must be made not only for the wire and accelerator, but also for the benzoic acid. This correction is found by running two or three blanks of 0.25 gram K C1 03, 0.25 gram acid and 10 grams Na,O, for each lot of chemicals and taking the average. From the total rise in degrees after the explosion of coke or ash sample, the blank correction is first subtracted, and the remainder multipled by 6234 (2×3117, as but 0.25 gram of sample instead. of 0.50 gram was used) to obtain the number of heat units. For the determination of ash in coke or ashes, but 0.50 gram is taken, as the combustion is slower with these substances.

Electric energy is not a primary energy; that is, it is not found in nature nor directly producible to any appreciable. extent from the stores of energy available in nature-water power and the energy of fuel. To become available for conversion into electric power, the energy found in nature must first be converted into mechanical rotation by some form of prime mover. The engineering characteristics of these converting apparatus may be classed under two main groups, those referring to economy and reliability, respectively. In both, the electric machine, whether generator or motor, ranges very high: its efficiency is virtually unity; its size, first cost, and maintenance small; its reliability great. In the cost of electric power the electric machine plays only a subordinate part; the essential element in determining the cost and the reliability of electric power is the prime mover; that is. the intermediary step between nature's stores of energy and the dynamo shaft.

The cost of electric power consists of three parts.

A. The fixed cost or permanent cost; that is, the cost depending on the size of the station, but not on the amount of power supplied by it.

B. The proportionate cost; that is, cost proportional to the amount of power delivered.

C. The reliability insurance; that is, the additional cost required to assure the desired reliability or continuity of service.

A. FIXED COST.

1. Interest on the investment in the plant. This factor varies very greatly with the form of the available energy. It is frequently