boilers, the proportions are—­ heating surface 9 square feet, fire grate 70 square inches, sectional area of tubes 10 square inches, sectional area of back uptake 12 square inches, sectional area of front uptake 10 square inches, sectional area of chimney 7 square inches, ratio of diameter of tube to length of tube 1/28th to 1/30th, cubical content of boiler exclusive of steam chest 6.5 cubic feet, cubical content of steam chest 1.5 cubic feet.

276. Q.—­These proportions do not apply to locomotive boilers?

A.—­Not at all.  In locomotive boilers the draught is maintained by the projection of the waste steam which escapes from the cylinders up the chimney, and the draught is much more powerful and the combustion much more rapid than in cases in which the combustion is maintained by the natural draught of a chimney, except indeed the chimney be of very unusual temperature and height.  The proportions proper for locomotive boilers will be seen by the dimensions of a few locomotives of approved construction, which have been found to give satisfactory results in practice, and which are recorded in the following Table: 

Name of Engine

Great Britain.    Pallas.       Snake.       Sphinx. 
Diameter of cylinder           18 in.      15 in.     14-1/4 in.    18 in. 
Length of stroke               24 in.      20 in.     21 in.        24 in. 
Diameter of driving wheel       8 ft.       6 ft.     6-1/2 ft.      5 ft. 
Inside diameter of fire box    53 in.      55 in.     41-1/3 in.    44 in. 
Inside width of fire box       63 in.      42 in.     43-1/4 in. 39-1/2in. 
Height of fire box above bars  63 in.      52 in.     48-1/3 in. 55-1/2in. 
Number of fire bars            29          ...  32               16
Thickness of fire bars         3/4 in.     1-3/4 in.  5/8 in.        1 in. 
Number of Tubes                305         134        181          142
Outside diameter of tubes      2 in.       2 in.      1-7/8 in.     2-1/8
in. 
Length of tubes                11 ft 3 in  10 ft 6 in 10 ft 3-1/2 in. 14
ft 3-1/4 in. 
Space between tubes            1/2 in.     3/4 in.    1/2 in. 
Inside diameter of ferules     1-9/16 in.  1-1/2 in.  1-5/16 in. 1-5/8 in. 
Diameter of chimney            17 in.      15 in.     13 in.    15-1/2 in. 
Diameter of blast orifice      5-1/2 in.    4-5/8 in. 4-1/2 in.  4-3/4 in. 
Area of grate                  21 sq. ft.  16.04 sqft 12.4 sq. ft.  10.56
sq. ft
Area of air space of grate     11.4 sqft   4.08 sqft  5.54 sq. ft.    5
sq. ft. 
Area of tubes                  5.46 sqft   2.40 sqft  2.8 sq. ft.  2.92
sq. ft. 
Area though ferules            4 sq. ft.   1.64 sqft  2 sq. ft.    2.04
sq. ft. 
Area of chimney                1.77 sqft   1.23 sqft  .921 sq. ft. 1.31
sq. ft. 
Area of blast orifice          23.76 sqin  16.8 sqin  14.18 sq. in. 17.7
sq. in. 
Heating surface of tubes       1627 sqft   668.7 sqft 823 sq. ft.  864
sq. ft.

THE BLAST IN LOCOMOTIVES.