180 Sioux City Academy of Science and Letters. 
Much of this residue is calcium carbonate, which is re- 
duced to calcium oxide after ignition of the lignite. Cal- 
cium sulphate and iron pyrites are also present to a slight 
extent. The iron pyrites is not thickly disseminated 
throughout the body of the material as in some coals, but 
often a concretion as large as an egg is found, upon which 
a great segregation of iron pyrites has taken place, thus 
removing it from the surrounding material. The pres- 
ence of iron oxide is noticeable in the ash. The source of 
the sulphur is the iron pyrite and the calcium sulphate, 
but the percentage of sulphur is low, and this fact is 
worthy of note. 
Assays made upon some of the iron pyrites from the 
lignite in Sec. 28 that was shipped to Denver, Colorado, 
by Mr. T. A. Black, of Sioux City, showed slight traces 
of gold and silver. 
Ultimate constituents—From the results in Table V as 
compared with those in Table II it appears that the per- 
centages of carbon are about what might be expected in 
each sample. The percentage of hydrogen seems to be 
a little low, but if in error the same condition has been 
maintained throughout the three determinations. Of 
nitrogen there is a little more than the normal amount in 
the Dakota County samples, and the oxygen, by differ- 
ence, is lower than might be expected in a carbonaceous 
material at this stage of alteration. 
Calorific power.—Taking these figures as they stand, 
the principles upon which they are made the basis of 
a calculation of the calorific power of the lignite may be 
explained as follows: <A calorie, the standard heat unit, 
represents the heat required to raise the temperature of 
1 kilogram of water from 4° C to 5° C. Berthelot and 
Bunte have determined that 1 kilogram of carbon (from 
wood charcoal) in burning to CO, produces 8,140 calories. 
One kilogram of hydrogen in burning to water (con- 
densed) produces 34,500 calories. One kilogram of sul- 
phur in burning water to SO, produces 2,220 calories. 
