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CEMENT, SAND AND STONE REQUIRED FOR WALLS OF SILOS.
(Thickness of walls, 6 inches. Doors, 26 inches wide. Proportions for concrete, 1:2:4.)
Bbls. of Cement Required For Cu. Yds. of Sand Required For Cu. Yds. of Gravel Req'd For
Given Inside Diameter in Feet. Given Inside Diameter in Feet. Given Inside Diameter in Feet.
10 12 14 16 18 20 10 12 | 14 16 18 20 10 12 14 16 18 | 20
5.8 7.0 8.4 9.3.
6.5

HEIGHT OF

SILO, FEET.

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16.0 19.0 22.625.4|
17.721.024.9]28.0|32.0

7.7 9.0 10.211.6

9.4 11.213.3|15.2 10.4 12.414.816.518.8

19.222.827.130.735.0 38.5 7.0 8.6 9.911.212.714.111.4 13.5 16.0 18.220.6 22.8
21.024.829.333.0 37.S41.8 7.7 9.110.7 12.113.7 15.3 12.4 14.7 17.4 19.6 22.224.S
22.3 26.631.5 35.5 40.6 44.9 S.2 9.7 11.6 13.0 14.8 16.413.3 15.818.721.0 24.0 26.5
24.028.8 33.838.243.448.0 8.7 10.5 12.3 14.0 15.817.5 14.217.019.822.8 25.5 28.5
25.7 30.7 36.0 40.5 46.051.4 9.4 11.213.114.816.918.715.0 18.0 21.3 24.027 330.3
27.132.338.3 43.449.051.3 10.0 11.814.0 15.8 17.9 19.9 16.119.222.5 25.5 29.032.0
28.734.240.445.852.057.5 10.5 12.5 14.8 16.8 19.021.0|17.0|20.3 24.027.230.634.0
30.336.242.8 48.755.0 60.8 11.113.3 15.7 17.820.122.218.021.525.428.732.5 35.9
31.737.844.550.657.564.0 11.6 14.0 16.4 18.621.223.6 18.8 22.426.430.034.038.0
33.540.047.453.7 60.5 67.5 12.3 14.7 17.3 19.5 22.124.6 19.9 23.823.031.7 35.640.0
11.849.655.8 65.3 71.0
15.3 18.1 20.4 23.926.0 |24.8 29.233.0 38.441.8
18.921.4|24.427.0
22.325.5 28.0
[26.3/29.6

51.8 58.666.574.0
61.2 69.876.6
171.680.01

30.6|34.7|39.3|43.5 36.0 41.045.0 42.3147.2

HEAT TRANSMITTED THROUGH ROOFING MATERIAL.

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108

Boiler Explosion Statistics.

BOILER EXPLOSION STATISTICs.

(From a paper read by F. S. Crum, at the First Industrial Safety Congress, Syracuse, N. Y.)
EXPLOSIONS IN THE UNITED STATES, 1868-1915.

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Killed
Injured. and
Injured.

YEAR ENDING
DECEMBER 31.

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814

1906.

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DISASTROUS BOILER EXPLOSIONS IN THE UNITED STATES, 1865-1916.

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109

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INTEREST TABLES FOR FARMERS WHO BORROW.

(By the Federal Farm Loan Board.)

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Below is a table showing the comparative cost on a $1,000 basis of a loan made on the thirty-six-year amortization plan, 5 per cent. interest, semi-annual payment, and a loan on the simple-interest plan at 5, 54, 6, 6, or 7 per cent., for any number of years from five to thirty-six, inclusive In order to find the difference in cost of a loan in any sum on the above amortization plan and a loan of like sum on the simpleinterest plan, (1) using the accompanying table, subtract the cost of a $1,000 Federal land bank loan for the time the desired loan will run from the cost of a $1,000 simple-interest loan at the specified rate for the same number of years; (2) multiply this difference by the number of times 1,000 is contained in the face of the desired loan.

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The above table shows the relative advantages of the various plans for buying land on instalments.

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American Equivalents.

3.94783 Winch' bu.

1.36 acres.

2204.62 lbs. av.

6 ft. sq.

1.41 inches.

4.5 bu.

1.22 acres.

Argentine Republic 34.1208 inches.
Central America... 132.87 inches.
Chili and Peru. 133.367 inches.

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133.384 inches.

|33.375 inches:

133 inches.

34 inches.

0.914117 yd,

33.384 inches.

2.707 gals. 71.1 sq. rods.' 0.663 mile.

41.98 acres.

Scotland & Ireland 5 quarters.

BIRD COUNT IN THE UNITED STATES.

(By E. W. Nelson. Chief of the Bureau of Biological Survey, United States Department of Agriculture.) EARLY in the summer of 1914 the Biological Survey of the United States Department of Agriculture took initial steps toward a count of the birds of the United States for the purpose of ascertaining approximately the number and relative abundance of the different species. This preliminary count proved to be so satisfactory that the Survey repeated it on a larger scale in 1915 and extended it over a still greater area in 1916 and 1917. The results obtained in 1914 have been surprisingly corroborated by those of succeeding years, and the work gives promise of producing, after a series of years, results that, in view of the recognized value of birds to agriculture, cannot fail to be of great value. It has been ascertained through these counts that birds in the agricultural districts in the Northeastern United States average slightly more than a pair to the acre, though in parts of the arid West and on the treeless plains this number dwindles. to an average of half a pair, or even less, to the acre.

By far the most abundant birds in the United States are the robin and the English sparrow, but several others are common enough to make their total numbers run well into the millions. The counts so far show that the most abundant bird on farms in the Northeastern States is the robin; next to this is the. English sparrow, and following these are the catbird, brown thrasher, house wren, kingbird, and bluebird, in the order named. The densest bird population anywhere recorded is hear Washington, D. C., where a careful count showed, in 1915, one hundred and thirty-five pairs of forty species on five acres. Two city blocks, well furnished with trees, in the city of Aiken, S. C., harbored sixty-five pairs on ten acres. These high figures show the important results which will follow from careful protection and encouragement of birds.

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WATER DRAWN FROM CATUN LAKE BY EVAPORATION.
(From the Canal Record.)

FVAPORATION from the surface of Gatun Lake in March, 1918, was the highest recorded since the filling. of the lake-8.475 inches, over an area of 165 square miles. The aggregate evaporated water amounted to 3,248,000.000 cubic feet, equivalent to 1,213 cubic feet for every second, day and night, in the month. The water drawn from the lake by evaporation in March exceeded slightly that used in operating the hydroelectric station at Gatun Spillway. The draft through the penstocks for the hydroelectric station was at the rate of 1,212 cuble feet per second. Had the water which the sun dres off been available for power it could have produced as much electricity as the hydroelectric station, the set output for which in Mare: was 4.681.000 kilowatt-hours. Approximately 740 cubic feet of water are used for each kilowatt at the hydroelectric station. where the effective head is approximately 75 feet. Under average conditions abou 2 times as much water is used by the hydroelectric station as is used in lockages. The water lost by evapt ration in March would have served for 22 complete lockages each day. During March the elevation of the lake's surface was lowered from 86.26 to 85.20 feet above sea level, or 1 foot and 7-10 of an inch. It has been calculated that had there been no useful losses of water, as for lockages, production of electricity, municipal uses, &c., tne surface would have remained practically stationary: that is, the inflow was just sumcient to equal the evaporation. During March 1.62 times as much water was lost by evaporation as flowed in through the Chagres River, as measured at Alhajuela. During the dry season the Chagres furnishes about 60 per cent of the lake inflow; for the year around It supplies about 40 per cent. Evaporation at the height of the dry season is much higher than in the rainy season. For the entire year the evaporation averages around 740 cubic feet per second. Hydroelectric consumption averaged 1,284 cubic feet per second in the calendar year 1917. The total evaporation in 1917 was 61 inches.

The current velocity of an average creek or small river in hilly or rolling country is normally two or three feet a second. At 21 feet per second, 740 cubic feet per second would be the discharge of a stream as wide as lower Broadway in New York City (approximately 80 feet, including the sidewalks) and 3.7 feet in depth, assuming an even, flume-like channel. Evaporation was considered in calculations for the formation of the lake, and although the loss of water through this process seems enormous there is yet an ample supply for the needs of the Canal.

It has been suggested that the creation of an inland body of water the size of Gatun Lake might result in a slight increase in precipitation, especially in the dry season, at stations on the leeward side of the lake. From a study of the records at present available, the conclusion is reached that the creation of Gatun Lake has had no appreciable effect on Isthmian rainfall, or that it has had such a slight effect that it will require a much longer period of records than is at present available to disclose even slight local increases in precipitation resulting from the increase in atmospheric humidity, due to evaporation from the lake surface.

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