CURVES CONSTRUCTION. 119 



By formula (3) the maximum load on a level is &amp;lt; 770 tons. 



By formula (2) the maximum grade for load of 76 tons is 250 feet. 



By formula (4) the maximum grade for 76 tons is 173 



By formula (1) the maximum load up a grade of 150 feet is 119J tons. 



By formula (3) the maximum load for same grade is 85 &quot; 



By formula (1) the maximum load on a 200-feet grade is 93 &quot; 



By formula (3) the maximum load on a 200-feet grade is 67 &quot; 



For a 30-ton engine on six drivers : 



The total adhesive weight is 67,200 Ibs. 



By formula (1) the maximum load on a level is 1 ,680 tons. 



By formula (2) the maximum grade up which this engine can draw a load of 



76 tons is 401 feet. 



By formula (4) the maximum grade for the same load is 281 &quot; 



By formula (1) the maximum load this engine can draw up a grade of 150 feet is. 186 tons. 



By formula (3) the maximum load for same grade is 133 &quot; 



By formula (1) the maximum load for grade of 200 feet is 146 &quot; 



By formula (3) the maximum load for the same grade is 104 J &quot; 



CURVES. 



On the Virginia Central road there are curves of 300 feet radius on a grade of 328 feet per 

 mile. 



On a level, trains run on curves of 300 feet radius at a velocity of 20 miles per hour. 



A radius of 150 feet, and even less, is practicable; but in such cases the velocity of the train 

 must be greatly diminished. 



There- are various formula for the calculation of the resistance on curves, but the simple inspec 

 tion of a wheel that has been some little time in use will show the inaccuracy of the results. 

 The formulas are based upon the supposition that the surface of the tire is conical ; this shape is 

 soon destroyed by what is called the channeling of the wheel. 



The resistances in question can probably be determined only by the result of many experi 

 ments with a dynanometer. 



On the Pennsylvania Central road the grade is reduced on curves at the rate of 0.025 per 100 

 feet per degree of curvature. 



CONSTRUCTION. 



To lay the rails. The road-bed being prepared, cross-ties placed, and iron distributed, a party 

 of six men will lay half a mile of track per day. 



The cross-ties should be prepared with corrosive sublimate; the sulphurets do not answer a 

 good purpose. 20,000 spruce cross-ties were prepared in this way, and laid in 1840; they are 

 now perfectly sound, although the natural duration of the wood is but Jive years. Cross-ties 

 average about twenty-five cents each. 



Shallow excavations may be covered with workmen. In the case of deep excavations, where the 

 earth cannot be removed laterally, sections of one-half mile, worked from both ends, are usually 

 most advantageous ; this distance, however, will depend chiefly upon the relation between the 

 established gradients and the natural surface of the ground. The end of a cut composed of 

 loose gravel or sand will accommodate a force capable of moving 15 to 20,000 yards in a month. 

 In one case, 26,000 cubic yards of sand were moved in that time, the average haul being three- 

 quarters of a mile. 



Long, deep cuts of gravel, sand, or similar deposite, can be opened, (working two levels at 

 each end,) with an average haul of one mile, at the rate of 15,000 to 25,000 cubic yards in 26 days. 



Ordinary gravel can be dug, thrown into a car, and moved an average haul of 1,000 feet for 



