166 NOTES ON COAL AND FUEL. 
produced " small purified coals, and the residue of the same, the pro- 
duce of a system for purifying coals ;" and, at the last English Exhibi- 
tion, the Americans produced purified coals, made up into light portable 
fuel. Patent fuel of compressed small coal is now largely made in 
"Wales for steamers. Dried turf, or peat, is extensively used in Ireland 
for fuel. 
In the sandy deserts of the north-east of Africa, the excrement from 
camels is dried and used as fuel, and other descriptions of excrement 
might be readily collected and burnt. Before railways became so uni- 
versally in vogue in England, cottagers in various parts of the country, 
particularly in Lincolnshire and Leicestershire, were in the habit of 
saving the refuse from their cow-stalls, laying it from three to three and 
a-half inches thick upon grass, and in its fresh and moist state cutting 
it into squares of about six inches, which they left to dry in the sun, 
and then stored for fuel in the winter. We have ourselves frequently 
witnessed this, and seen the square or round stacks of the fuel thatched 
down for domestic use when coals became dear, or winter weather de- 
manded more numerous fires than ordinary. The Chinese have for ages 
been accustomed to mix the excrement from cows and other refuse vege- 
table matter, with soft clay and coal-dust, thus forming cakes that, when 
sun-baked, become a cheap and portable fuel, and they burn with very 
little smoke. These cakes are, indeed, largely manufactured in the coal 
districts of Northern China, being widely distributed therefrom over that 
vast empire by means of junks on the numerous canals. In some parts 
of Wales, particularly in Pembrokeshire, culm is frequently made into 
balls with clay, and the poorer classes sit over them for hours in winter, 
when lighted in the cottage grates. 
It will be well for people to bear in mind, that upon the stowage 
away of large quantities of coals at ordinary temperatures, a slow com- 
bustion is going on under the action of the oxygen of the atmosphere, 
evolving carbonic acid, nitrogen, and inflammable gases, which may lead 
to explosions, the combustion being the more promoted by high tempe- 
rature, combined with the presence of moisture. If the coals contain 
much sulphur or iron pyrites, the chemical action may become so 
intense as very speedily to fire them. In storing coals, therefore, it is 
important to keep them dry, and of such a variety as may be the least 
liable to progressive decomposition. 
