Chapter 2

Take the test previously mentioned, for example. The evaporation from and at 212° F. or the equivalent evaporation, was 7.5 pounds of water per pound of coal. The weight of coal burned per hour was 5,000 ÷ 10 = 500 pounds. Then the equivalent evaporation was 7.5 × 500 = 3,750 pounds per hour. According to the foregoing definition of a boiler horsepower, then--

3,750 Boiler horsepower = ----- = 109. 34.5

The "rated horsepower" of a boiler, or the "builders' rating," is the number of square feet of heating surface in the boiler divided by a number. In the case of stationary boilers this number is 10 or 12, but 10 is very commonly taken as the amount of heating surface per horsepower. Assuming this value and assuming further that the boiler tested had 1,500 square feet of heating surface, its rated horsepower would be 1,500 ÷ 10 = 150 boiler horsepower.

It is often desirable to know what per cent of the rated capacity is developed in a test. This is found by dividing the horsepower developed during the test by the builders' rating. In the case of the boiler tested, 109 horsepower was developed. The percentage of rated capacity developed, therefore, was 109 ÷ 150 = 0.73, or 73 per cent.

HEATING SURFACE.

The heating surface of a boiler is the surface of metal exposed to the fire or hot gases on one side and to water on the other side. Thus, the internal surface of the tubes of a fire-tube boiler is the heating surface of the tubes, but the outside surface of the tubes of a water-tube boiler is the heating surface of those tubes. In addition to the tubes, all other surfaces which have hot gases on one side and water on the other must be taken into account. For instance, in a fire-tube boiler from one-half to two-thirds of the shell (depending on how the boiler is set) acts as heating surface. In addition to this, the surface presented by both heads, below the water level, has to be computed. The heating surface of each head is equal to two-thirds its area minus the total area of the holes cut away to receive the tubes.

COST OF EVAPORATION.

The cost of evaporation is usually stated as the cost of fuel required to evaporate 1,000 pounds of water from and at 212° F. To find it, multiply the price of coal per ton by 1,000 and divide the result by the product of the equivalent evaporation per pound of coal and the number of pounds in a ton.

Suppose that the cost of the coal used in the foregoing test was $3.60 per ton of 2,000 pounds. The equivalent evaporation per pound of coal was 7.5 pounds. Therefore the cost of evaporating 1,000 pounds of water from 180° F. to steam at 100-pound gage, is--

$3.60 × 1,000 ------------- = $0.24, or 24 cents. 7.5 × 2,000

TABLE OF TEST RESULTS.

After the test has been made and properly worked up, as heretofore described, collect all the results of the test on one sheet, so that they can be kept in convenient form for reference and for comparison with later tests. A brief form of arranging the results is as follows:

1. Date of test May 20, 1918 2. Duration of test hours 10 3. Weight of coal used pounds 5,000 4. Weight of water fed and evaporated do. 35,000 5. Average steam pressure, gauge do. 100 6. Average feed-water temperature °F. 180 7. Factor of evaporation 1.0727 8. Equivalent evaporation from and at 212° F. pounds 37,545

EFFICIENCY.

9. Efficiency of boiler and furnace per cent 54

CAPACITY.

10. Boiler horsepower developed 109 11. Builders' rated horsepower 150 12. Percentage of rated horsepower developed per cent 73

ECONOMIC RESULTS.

13. Actual evaporation per pound of coal pounds 7 14. Equivalent evaporation from and at 212° F. per pound of coal as fired, pounds 7.5 15. Cost of coal per ton (2,000 pounds) $3.60 16. Cost of coal to evaporate 1,000 pounds from and at 212° F. $0.24

HOW TO USE THE TEST RESULTS.

The object of working up a test is to obtain a clear idea as to the efficiency of operation of the boiler or its operating cost. Consequently, after the calculations have been made, they should be used as a basis for study with the idea of improving the boiler performance.

Take the matter of boiler efficiency, for example, as found from the test mentioned. Its value was 54 per cent. This is altogether too low and indicates wasteful operation. The efficiency of a hand-fired boiler ought not to be less than 65 per cent, and it can be increased to 70 per cent by careful management under good conditions.

The chart in figure 3 can be used to indicate the evaporation that should be obtained in order to reach a desired efficiency. Suppose, for example, that it is desired to know how much water per pound of coal must be evaporated to produce a boiler efficiency of 65 per cent with coal having a heating value of 13,500 B. t. u. per pound.

Locate 13,500 at the bottom of the chart, follow the vertical line until it meets the diagonal marked 65 per cent, and then from this point follow the horizontal line to the left-hand edge, where the figure 9 is found. This means that the equivalent evaporation from and by 212° F. per pound of coal must be 9 pounds of water. If the steam pressure is 100 pounds gauge, and the feed-water temperature is 180° F. the factor of evaporation is 1.0727, then the actual evaporation must be 9 ÷ 1.0727 = 8.36 pounds per pound of coal. In other words, to increase the efficiency from 54 per cent to 65 per cent under the same conditions of pressure and feed-water temperature, it would be necessary to increase the actual evaporation from 7 pounds to 8.36 pounds. This would mean practically 20 per cent more steam from the same weight of coal used.

How to do this will require some study and experimenting on the part of the fireman or engineer. The three most common reasons for low-boiler efficiency are (1) excess air, (2) dirty heating surfaces, and (3) loss of coal through the grates. _The first of these items is the most important of the three._ In most cases the greatest preventable waste of coal in a boiler plant is directly due to excess air. Excess air simply means the amount of air which gets into the furnace and boiler which is not needed for completing the combustion of the coal. Very often twice as much air is admitted to the boiler setting as is required. This extra or excess air is heated and carries heat out through the chimney instead of heating the water in the boiler to make steam. There are two ways in which this excess air gets into the furnace and boiler setting. First, by a combination of bad regulation of drafts and firing. The chances are your uptake damper is too wide open. Try closing it a little. Then, there may be holes in the fire. Keep these covered. The second way excess air occurs is by leakage through the boiler setting, through cracks in the brickwork, leaks around the frames and edges of cleaning doors, and holes around the blow-off pipes. There are also other places where such air can leak in.

Take a torch or candle and go over the entire surface of your boiler setting--front, back, sides, and top. Where the flame of the torch is drawn inward there is an air leak. Plaster up all air leaks and repair the brickwork around door frames where necessary. You should go over your boiler for air leaks once a month.

In regard to best methods of firing soft coal, see Technical Paper No. 80 of the Bureau of Mines, which may be obtained from your State Fuel Administrator.

Dirty heating surfaces cause low efficiency because they prevent the heat in the hot gases from getting through into the water. Therefore, keep the shell and tubes free of soot on one side and scale on the other. Soot may be removed by the daily use of blowers, scrapers, and cleaners. The problem of scale and pure feed water is a big one and should be taken up with proper authorities on the subject.

There are many things that may be done to increase the efficiency of the boiler and to save coal. For convenience a number of these points are grouped in the following list:

WHAT TO DO. | WHY. | 1. Close up all leaks in the boiler | To prevent waste of heat due to setting. | excess air admitted. | 2. Keep shell and tubes free from | To allow the heat to pass easily soot and scale. | into the water. | 3. Use grates suited to the fuel | To prevent loss of unburnt coal to be burned. | through air spaces. | 4. Fire often, and little at a | To obtain uniform conditions and time. | better combustion. | 5. Cover all thin spots and keep | To prevent burning holes in bed fire bed level. | and admitting excess air. | 6. Do not allow clinkers to form | Because they reduce the effective on side or bridge walls. | area of the grate. | 7. Keep the ash pit free from ashes | To prevent warping and burning out and hot clinkers. | of the grates. | 8. Do not stir the fire except when | Because stirring causes clinker necessary. | and is likely to waste coal. | 9. Use damper and not ash-pit doors | Because less excess air is to control draft. | admitted by so doing. | 10. See that steam pipes and valves | Because steam leaks waste heat are tight. | and therefore coal. | 11. Keep blow-off valves tight. | Because leaks of hot water waste | coal. | 12. Cover steam pipes and the tops | To prevent radiation and loss of of boilers. | heat.

Make a boiler test under the conditions of operation as they now exist in your plant. Then make all possible improvements as suggested in this bulletin, make another test afterwards and note the increase in the equivalent evaporation per pound of coal used.

Remember that the _firing line_ in the boiler room can be just as patriotic and helpful as the _firing line_ at the front.

_Table of factors of evaporation._

============================================================================ Feed | Steam pressure in pounds per square inch, gauge. temperature,|--------------------------------------------------------------- °F. | 30 | 50 | 70 | 80 | 90 | 100 | 110 | 120 ------------+-------+-------+-------+-------+-------+-------+-------+------- 32 | 1.2073| 1.2144| 1.2195| 1.2216| 1.2234| 1.2251| 1.2266| 1.2279 35 | 1.2042| 1.2113| 1.2164| 1.2184| 1.2203| 1.2219| 1.2235| 1.2248 38 | 1.2011| 1.2082| 1.2133| 1.2153| 1.2172| 1.2188| 1.2204| 1.2217 41 | 1.1980| 1.2051| 1.2102| 1.2122| 1.2141| 1.2157| 1.2173| 1.2186 44 | 1.1949| 1.2020| 1.2071| 1.2091| 1.2110| 1.2126| 1.2142| 1.2155 47 | 1.1918| 1.1989| 1.2040| 1.2060| 1.2079| 1.2095| 1.2111| 1.2124 50 | 1.1887| 1.1958| 1.2009| 1.2029| 1.2048| 1.2064| 1.2080| 1.2093 53 | 1.1856| 1.1927| 1.1978| 1.1998| 1.2017| 1.2033| 1.2049| 1.2062 56 | 1.1825| 1.1896| 1.1947| 1.1967| 1.1986| 1.2002| 1.2018| 1.2031 59 | 1.1794| 1.1865| 1.1916| 1.1937| 1.1955| 1.1972| 1.1987| 1.2000 62 | 1.1763| 1.1835| 1.1885| 1.1906| 1.1924| 1.1941| 1.1956| 1.1970 65 | 1.1733| 1.1804| 1.1854| 1.1875| 1.1893| 1.1910| 1.1925| 1.1939 68 | 1.1702| 1.1773| 1.1823| 1.1844| 1.1862| 1.1879| 1.1894| 1.1908 71 | 1.1671| 1.1742| 1.1792| 1.1813| 1.1832| 1.1848| 1.1864| 1.1877 74 | 1.1640| 1.1711| 1.1762| 1.1782| 1.1801| 1.1817| 1.1833| 1.1846 77 | 1.1609| 1.1680| 1.1731| 1.1751| 1.1770| 1.1786| 1.1802| 1.1815 80 | 1.1578| 1.1650| 1.1700| 1.1721| 1.1739| 1.1756| 1.1771| 1.1785 83 | 1.1548| 1.1619| 1.1669| 1.1690| 1.1708| 1.1725| 1.1740| 1.1754 86 | 1.1518| 1.1588| 1.1638| 1.1659| 1.1678| 1.1694| 1.1710| 1.1723 89 | 1.1486| 1.1557| 1.1608| 1.1628| 1.1647| 1.1663| 1.1679| 1.1692 92 | 1.1455| 1.1526| 1.1577| 1.1597| 1.1616| 1.1632| 1.1648| 1.1661 95 | 1.1424| 1.1495| 1.1546| 1.1566| 1.1585| 1.1602| 1.1617| 1.1630 98 | 1.1393| 1.1465| 1.1515| 1.1536| 1.1554| 1.1571| 1.1586| 1.1600 101 | 1.1363| 1.1434| 1.1484| 1.1505| 1.1523| 1.1540| 1.1555| 1.1569 104 | 1.1332| 1.1403| 1.1453| 1.1474| 1.1492| 1.1509| 1.1525| 1.1538 107 | 1.1301| 1.1372| 1.1423| 1.1443| 1.1462| 1.1478| 1.1494| 1.1507 110 | 1.1270| 1.1341| 1.1392| 1.1412| 1.1431| 1.1447| 1.1463| 1.1476 113 | 1.1239| 1.1310| 1.1360| 1.1382| 1.1400| 1.1417| 1.1432| 1.1445 116 | 1.1209| 1.1280| 1.1330| 1.1351| 1.1369| 1.1386| 1.1401| 1.1415 119 | 1.1178| 1.1249| 1.1299| 1.1320| 1.1339| 1.1355| 1.1370| 1.1384 122 | 1.1147| 1.1218| 1.1269| 1.1289| 1.1308| 1.1324| 1.1340| 1.1353 125 | 1.1116| 1.1187| 1.1238| 1.1258| 1.1277| 1.1293| 1.1309| 1.1322 128 | 1.1085| 1.1156| 1.1207| 1.1227| 1.1246| 1.1262| 1.1278| 1.1291 131 | 1.1054| 1.1125| 1.1176| 1.1197| 1.1215| 1.1232| 1.1247| 1.1260 134 | 1.1023| 1.1095| 1.1145| 1.1166| 1.1184| 1.1201| 1.1216| 1.1230 137 | 1.0993| 1.1064| 1.1114| 1.1135| 1.1153| 1.1170| 1.1185| 1.1199 140 | 1.0962| 1.1033| 1.1083| 1.1104| 1.1123| 1.1139| 1.1154| 1.1168 143 | 1.0931| 1.1002| 1.1052| 1.1073| 1.1092| 1.1108| 1.1124| 1.1137 146 | 1.0900| 1.0971| 1.1022| 1.1042| 1.1061| 1.1077| 1.1093| 1.1106 149 | 1.0869| 1.0940| 1.0991| 1.1011| 1.1030| 1.1046| 1.1062| 1.1075 152 | 1.0838| 1.0909| 1.0960| 1.0980| 1.0999| 1.1015| 1.1031| 1.1044 155 | 1.0807| 1.0878| 1.0929| 1.0950| 1.0968| 1.0985| 1.1000| 1.1013 158 | 1.0776| 1.0847| 1.0898| 1.0919| 1.0937| 1.0954| 1.0969| 1.0982 161 | 1.0745| 1.0817| 1.0867| 1.0888| 1.0906| 1.0923| 1.0938| 1.0952 164 | 1.0715| 1.0786| 1.0836| 1.0857| 1.0875| 1.0892| 1.0907| 1.0921 167 | 1.0684| 1.0755| 1.0805| 1.0826| 1.0844| 1.0861| 1.0876| 1.0890 170 | 1.0653| 1.0724| 1.0774| 1.0795| 1.0813| 1.0830| 1.0845| 1.0859 172 | 1.0632| 1.0703| 1.0754| 1.0774| 1.0793| 1.0809| 1.0825| 1.0838 174 | 1.0611| 1.0683| 1.0733| 1.0754| 1.0772| 1.0789| 1.0804| 1.0817 176 | 1.0591| 1.0662| 1.0712| 1.0733| 1.0752| 1.0768| 1.0783| 1.0797 178 | 1.0570| 1.0641| 1.0692| 1.0712| 1.0731| 1.0747| 1.0763| 1.0776 180 | 1.0549| 1.0621| 1.0671| 1.0692| 1.0710| 1.0727| 1.0742| 1.0756 182 | 1.0529| 1.0600| 1.0650| 1.0671| 1.0690| 1.0706| 1.0721| 1.0735 184 | 1.0508| 1.0579| 1.0630| 1.0650| 1.0669| 1.0685| 1.0701| 1.0714 186 | 1.0488| 1.0559| 1.0609| 1.0630| 1.0648| 1.0665| 1.0680| 1.0694 188 | 1.0467| 1.0538| 1.0588| 1.0609| 1.0628| 1.0644| 1.0660| 1.0673 190 | 1.0446| 1.0517| 1.0568| 1.0588| 1.0607| 1.0623| 1.0639| 1.0652 192 | 1.0425| 1.0497| 1.0547| 1.0568| 1.0586| 1.0603| 1.0618| 1.0632 194 | 1.0405| 1.0476| 1.0526| 1.0547| 1.0566| 1.0582| 1.0597| 1.0611 196 | 1.0384| 1.0455| 1.0506| 1.0526| 1.0545| 1.0561| 1.0577| 1.0590 198 | 1.0363| 1.0435| 1.0485| 1.0506| 1.0524| 1.0541| 1.0556| 1.0570 200 | 1.0343| 1.0414| 1.0464| 1.0485| 1.0504| 1.0520| 1.0535| 1.0549 202 | 1.0322| 1.0393| 1.0444| 1.0464| 1.0483| 1.0499| 1.0515| 1.0528 204 | 1.0301| 1.0372| 1.0423| 1.0444| 1.0462| 1.0479| 1.0494| 1.0507 206 | 1.0281| 1.0352| 1.0402| 1.0423| 1.0441| 1.0458| 1.0473| 1.0487 208 | 1.0260| 1.0331| 1.0381| 1.0402| 1.0421| 1.0437| 1.0453| 1.0466 210 | 1.0239| 1.0310| 1.0361| 1.0381| 1.0400| 1.0416| 1.0432| 1.0445 212 | 1.0218| 1.0290| 1.0340| 1.0361| 1.0379| 1.0396| 1.0411| 1.0425 ----------------------------------------------------------------------------

_Table of factors of evaporation_--Concluded.

============================================================================ Feed | Steam pressure in pounds per square inch, gauge. temperature,|--------------------------------------------------------------- °F. | 130 | 140 | 150 | 160 | 170 | 180 | 190 | 200 ------------+-------+-------+-------+-------+-------+-------+-------+------- 32 | 1.2292| 1.2304| 1.2315| 1.2324| 1.2333| 1.2342| 1.2351| 1.2358 35 | 1.2261| 1.2273| 1.2283| 1.2293| 1.2302| 1.2311| 1.2320| 1.2327 38 | 1.2230| 1.2242| 1.2252| 1.2262| 1.2271| 1.2280| 1.2288| 1.2296 41 | 1.2199| 1.2211| 1.2221| 1.2231| 1.2240| 1.2249| 1.2257| 1.2265 44 | 1.2168| 1.2180| 1.2190| 1.2200| 1.2209| 1.2218| 1.2226| 1.2234 47 | 1.2137| 1.2149| 1.2159| 1.2168| 1.2178| 1.2187| 1.2195| 1.2202 50 | 1.2106| 1.2118| 1.2128| 1.2137| 1.2147| 1.2156| 1.2164| 1.2171 53 | 1.2075| 1.2087| 1.2097| 1.2107| 1.2116| 1.2125| 1.2133| 1.2141 56 | 1.2044| 1.2056| 1.2066| 1.2076| 1.2085| 1.2094| 1.2102| 1.2110 59 | 1.2013| 1.2025| 1.2035| 1.2045| 1.2054| 1.2063| 1.2072| 1.2079 62 | 1.1982| 1.1994| 1.2005| 1.2014| 1.2023| 1.2032| 1.2041| 1.2048 65 | 1.1951| 1.1963| 1.1974| 1.1983| 1.1992| 1.2002| 1.2010| 1.2017 68 | 1.1920| 1.1933| 1.1943| 1.1952| 1.1961| 1.1971| 1.1979| 1.1986 71 | 1.1889| 1.1902| 1.1912| 1.1921| 1.1931| 1.1940| 1.1948| 1.1955 74 | 1.1859| 1.1871| 1.1881| 1.1890| 1.1900| 1.1909| 1.1917| 1.1924 77 | 1.1828| 1.1840| 1.1850| 1.1860| 1.1869| 1.1878| 1.1886| 1.1894 80 | 1.1797| 1.1809| 1.1820| 1.1829| 1.1838| 1.1847| 1.1856| 1.1863 83 | 1.1766| 1.1778| 1.1789| 1.1798| 1.1807| 1.1817| 1.1825| 1.1832 86 | 1.1735| 1.1748| 1.1758| 1.1767| 1.1776| 1.1786| 1.1794| 1.1801 89 | 1.1704| 1.1717| 1.1727| 1.1736| 1.1746| 1.1755| 1.1763| 1.1770 92 | 1.1674| 1.1686| 1.1696| 1.1705| 1.1715| 1.1724| 1.1732| 1.1739 95 | 1.1643| 1.1655| 1.1665| 1.1675| 1.1684| 1.1693| 1.1701| 1.1709 98 | 1.1612| 1.1624| 1.1635| 1.1644| 1.1653| 1.1662| 1.1671| 1.1678 101 | 1.1581| 1.1593| 1.1604| 1.1613| 1.1622| 1.1632| 1.1640| 1.1647 104 | 1.1550| 1.1563| 1.1573| 1.1582| 1.1592| 1.1601| 1.1609| 1.1616 107 | 1.1519| 1.1532| 1.1542| 1.1551| 1.1561| 1.1570| 1.1578| 1.1585 110 | 1.1489| 1.1501| 1.1511| 1.1521| 1.1530| 1.1539| 1.1547| 1.1555 113 | 1.1458| 1.1470| 1.1481| 1.1490| 1.1499| 1.1508| 1.1515| 1.1524 116 | 1.1427| 1.1439| 1.1450| 1.1459| 1.1468| 1.1478| 1.1486| 1.1493 119 | 1.1396| 1.1409| 1.1419| 1.1428| 1.1437| 1.1447| 1.1455| 1.1462 122 | 1.1365| 1.1378| 1.1388| 1.1397| 1.1407| 1.1416| 1.1424| 1.1431 125 | 1.1335| 1.1347| 1.1357| 1.1366| 1.1376| 1.1385| 1.1393| 1.1400 128 | 1.1304| 1.1316| 1.1326| 1.1336| 1.1345| 1.1354| 1.1362| 1.1370 131 | 1.1273| 1.1285| 1.1295| 1.1305| 1.1314| 1.1323| 1.1332| 1.1339 134 | 1.1242| 1.1254| 1.1265| 1.1274| 1.1283| 1.1292| 1.1301| 1.1308 137 | 1.1211| 1.1224| 1.1234| 1.1243| 1.1252| 1.1262| 1.1270| 1.1277 140 | 1.1180| 1.1193| 1.1203| 1.1212| 1.1221| 1.1231| 1.1239| 1.1246 143 | 1.1149| 1.1162| 1.1172| 1.1181| 1.1191| 1.1200| 1.1208| 1.1215 146 | 1.1119| 1.1131| 1.1141| 1.1150| 1.1160| 1.1169| 1.1177| 1.1184 149 | 1.1088| 1.1100| 1.1110| 1.1120| 1.1129| 1.1138| 1.1146| 1.1154 152 | 1.1057| 1.1069| 1.1079| 1.1089| 1.1098| 1.1107| 1.1115| 1.1123 155 | 1.1026| 1.1038| 1.1048| 1.1058| 1.1067| 1.1076| 1.1085| 1.1092 158 | 1.0995| 1.1007| 1.1018| 1.1027| 1.1036| 1.1045| 1.1054| 1.1061 161 | 1.0964| 1.0976| 1.0987| 1.0996| 1.1005| 1.1014| 1.1023| 1.1030 164 | 1.0933| 1.0945| 1.0956| 1.0965| 1.0974| 1.0984| 1.0992| 1.0999 167 | 1.0902| 1.0914| 1.0925| 1.0934| 1.0943| 1.0953| 1.0961| 1.0968 170 | 1.0871| 1.0883| 1.0894| 1.0903| 1.0912| 1.0922| 1.0930| 1.0937 172 | 1.0850| 1.0863| 1.0873| 1.0882| 1.0892| 1.0901| 1.0909| 1.0916 174 | 1.0830| 1.0842| 1.0853| 1.0862| 1.0871| 1.0880| 1.0889| 1.0896 176 | 1.0809| 1.0822| 1.0832| 1.0841| 1.0850| 1.0860| 1.0868| 1.0875 178 | 1.0789| 1.0801| 1.0811| 1.0820| 1.0830| 1.0839| 1.0847| 1.0854 180 | 1.0768| 1.0780| 1.0791| 1.0800| 1.0809| 1.0818| 1.0827| 1.0834 182 | 1.0747| 1.0760| 1.0770| 1.0779| 1.0788| 1.0798| 1.0806| 1.0813 184 | 1.0727| 1.0739| 1.0749| 1.0759| 1.0768| 1.0777| 1.0785| 1.0793 186 | 1.0706| 1.0718| 1.0729| 1.0738| 1.0747| 1.0756| 1.0765| 1.0772 188 | 1.0685| 1.0698| 1.0708| 1.0717| 1.0727| 1.0736| 1.0744| 1.0751 190 | 1.0665| 1.0677| 1.0687| 1.0697| 1.0706| 1.0715| 1.0723| 1.0731 192 | 1.0644| 1.0656| 1.0667| 1.0676| 1.0685| 1.0694| 1.0703| 1.0710 194 | 1.0623| 1.0636| 1.0646| 1.0655| 1.0664| 1.0674| 1.0682| 1.0689 196 | 1.0603| 1.0615| 1.0625| 1.0635| 1.0644| 1.0653| 1.0661| 1.0669 198 | 1.0582| 1.0594| 1.0605| 1.0614| 1.0623| 1.0632| 1.0641| 1.0648 200 | 1.0561| 1.0574| 1.0584| 1.0593| 1.0602| 1.0612| 1.0620| 1.0627 202 | 1.0541| 1.0553| 1.0563| 1.0572| 1.0582| 1.0591| 1.0599| 1.0606 204 | 1.0520| 1.0532| 1.0542| 1.0552| 1.0561| 1.0570| 1.0579| 1.0586 206 | 1.0499| 1.0511| 1.0522| 1.0531| 1.0540| 1.0550| 1.0558| 1.0565 208 | 1.0478| 1.0491| 1.0501| 1.0510| 1.0520| 1.0529| 1.0537| 1.0544 210 | 1.0458| 1.0470| 1.0480| 1.0490| 1.0499| 1.0508| 1.0516| 1.0524 212 | 1.0437| 1.0449| 1.0460| 1.0469| 1.0478| 1.0487| 1.0496| 1.0503

PUBLICATIONS ON THE UTILIZATION OF COAL AND LIGNITE.

A limited supply of the following publications of the Bureau of Mines has been printed and is available for free distribution until the edition is exhausted. Requests for all publications can not be granted, and to insure equitable distribution applicants are requested to limit their selection to publications that may be of especial interest to them. Requests for publications should be addressed to the Director, Bureau of Mines.

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PUBLICATIONS AVAILABLE FOR FREE DISTRIBUTION.

BULLETIN 58. Fuel briquetting investigations, July, 1904, to July, 1912, by C. A. Wright. 1913. 277 pp., 21 pls., 3 figs.

BULLETIN 76. United States coals available for export trade, by Van. H. Manning. 1914. 15 pp., 1 pl.

BULLETIN 85. Analyses of mine and car samples of coal collected in the fiscal years 1911 to 1913, by A. C. Fieldner, H. I. Smith, A. H. Fay, and Samuel Sanford. 1914. 444 pp., 2 figs.