214 KANSAS CITY REVIEW OF SCIENCE. 
tive value of different coals supplied to the United States army for fuel, and the 
equivalent value of the same coal as compared with cords of oak wood, and have 
every appearance of having been carefully and faithfully carried out. The meas- 
ure of value is the quantity of water evaporated from and at 212° F. per pound 
of coal. The experiments in question were with an improved vertical water tube 
boiler designed by General Meigs, and built for this express purpose. The data 
gi^en below are all from experiments with this boiler. It is only a portion of the 
whole experiment. 
Semi-bituminous coal, Somerset County, Penn., 88.99 W^ cent of combusti- 
ble, 9.85 pounds of water; semi-bituminous of another grade, from the same 
county, 90.92 per cent of combustible, 97.5 pounds of water ; Wilkesbarre anthra- 
cite from Black Diamond mine, 80.77 per cent of combustible, 9.37 evaporation; 
Scranton anthracite to D. & H. C. Co., 77.3 per cent combustible, 9.28 pounds 
water; Lykens Valley anthracite, 93.87 per cent combustible, 9.07 pounds water ; 
Los Cerrillos anthracite. New Mexico, 88.25 per cent combustible, 9.04, pounds 
water; Scranton anthracite D. L. & W. R. R. Co., 82.85 P^^ (^^"sW. combustible,. 
8.87 pounds water; bituminous coal near Pittsburg, 94.04 per cent combustible, 
8.78 pounds water; Los Cerrillos, bituminous, New Mexico, 86.74 P^r cent 
combustible, 8.60 pounds water ; West Virginia splint, 91.9 per cent combusti- 
ble, 8.34 pounds water; Scotch splint from Glasgow, Scotland, 93.28 per cent 
combustible, 7.61 pounds water; Davison, West Hartley, 94.01 per cent com^- 
bustible, 7.6 pounds water; South Wellington, Vancouver's Island, 91.83 per 
cent combustible, 7. 59 pounds water ; Cow Pen, West Hartley, England, 93.89 
per cent combustible, 7.52 pounds water; Indiana cannel coal, Davis County, 
Indiana, 75.18 per cent combutible, 7.32 pounds water; Wellington coal, Well- 
ington mine, Vancouver's Island, 90.62 per cent combustible,. 6.71 pounds water ; 
bituminous coal Canon City, Colorado, 90 per cent combustible, 6.45 pounds water ;. 
Eastport, Coos Bay, Oregon, 91.16 per cent combustible, 5.24 pounds water; 
Weber coal. Chalk Creek, Summit County, Utah, 89.98 per cent combustible, 
4.73 pounds water; lignite coal, from Dakota, 93,77 per cent combustible, 4.03 
pounds water. 
In the first specimen of coal, 1521 pounds was equivalent to a cord of oak 
wood ; the last named required 3712 pounds of coal as the equivalent of one cord of 
oak wood, and the variation was constant; beginning with the first item, at 1521, 
a continual progression is made, showing that each coal that follows was less and 
less in value both in evaporative efficiency and in real efficiency as compared 
with oak wood. There is also another very important point which the users of 
coal will profit by studying. The percentage of combustible in coal is no index 
whatever of the evaporative efficiency of the coal in the same boiler. The per- 
centage of combustible has been one of the points about which theoretical en- 
gineers have had immense arguments; immense, perhaps, in their prolixity,, 
vague in meaning, entirely indefinite and indeterminate. As an actual fact, 
which General Meigs has settled most effectually, the semi-bituminous coal proves 
to be the most valuable, and while the percentage of combustible in the first item-. 
