44 OPERATIONS OF FUEL-TESTING PLANT IN 1905. 
The wax tailings used in these investigations were obtained from the Standard Oil Com- 
pany. They melt at a temperature of about 70° C. From 4 to 6 per cent of this material 
would prove satisfactory in the briquettes. The amount of this material produced in the 
United States is small and the price is about 6 cents per gallon. This would make the 
binding material used in a ton of briquettes cost approximately 45 to 60 cents. 
Tests made with acid sludge as a binder were not satisfactory. It not only added the 
unwelcome sulphur, but its binding qualities were very inferior. 
Asphalt tar was found unsatisfactory as a binder even when 8 to 12 per cent was used, 
inasmuch as the briquettes fell to pieces in the fire; but its use for waterproofing when 
starch or other material had been used as a binder proved fairly satisfactory. 
Pintsch-gas tar, produced by heating petroleum oil in iron retorts at a high temperature, 
was obtainable in so small a quantity that only preliminary tests were made covering its 
use as a binder and these were only partially satisfactory. 
REQUISITES FOR BINDING MATERIALS. 
The results of the investigations in the laboratory of the fuel-testing plant and the 
writer's observations in briquetting plants in other countries point to certain general con- 
clusions concerning the requisites of satisfactory binding materials for use in the manu- 
facture of briquettes. 
In the making of coal briquettes the binding work is best performed when the particles 
of coal are coated and when the void spaces are filled with the binding material. This is 
best accomplished when the temperature of the mixture before compression is raised suf- 
ficiently to liquefy or vaporize the binder. 
The relation between the coal and the binder seems to be physical rather than chemical, 
though it is possible that certain minor chemical changes may accompany the briquetting 
operation. 
The amount of the binding material necessary will therefore depend on the aggregate 
of the surfaces of the coal particles to be coated, on the void spaces to be filled, and on 
the general physical and chemical character of the coal. Coking coals require less binder 
than noncoking coals, and the percentage of binder necessary for the latter coals may, in 
many cases, be diminished and the quality of the briquette otherwise improved by the 
previous admixture with them of from 10 to 20 per cent of some coking coal. 
Furthermore, when a coal is finely pulverized, a result which frequently follows pro- 
tracted slacking on exposure to the weather, the briquetting of such material is facilitated 
by the mixture of a considerable percentage of the same or another coal — preferably a 
nonslacking coal — crushed to sizes ranging from one-sixteenth inch to one-fourth inch. 
The following are mentioned as the more important requisites of a suitable binding 
ma'erial for use in the manufacture of briquettes: 
(1) It must be inexpensive, because of the small difference in the United States between 
the prices of slack or fine coal and those of lump coal. This difference in some regions is 
practically nothing, as in the Pocahontas coal fields of West Virginia; while in a number 
of other fields, as in portions of Indiana, Illinois, Arkansas, etc., it may reach $1 or even 
$1.50 a ton. 
(2) It should be capable of abundant production in different parts of the country, in 
order to avoid the necessity for long transportation. 
(3) It should be of such character as to make it easily handled and applied at workable 
temperatures. If it is used in solid condition, as in the case of pitch, the melting point 
should not be lower than the temperature of hot summer days, nor ordinarily above that 
of live steam. 
(4) It should hold the briquette together strongly, not only during ordinary handling 
and transportation, but also during protracted exposure to the weather and while burning. 
Certain materials, like starch and molasses, yield fairly satisfactory results as long as the 
briquettes are kept dry and during their consumption by fire; but as these materials are 
soluble in water, the briquettes in which they are used as a binder go to pieces under the 
