2 
THE TROPICAL AGRICULTURIST. 
[July 2, 1888. 
of the shales which are so plentiful in many 
parts of Britain. Whether it be natural oil from 
wells bored in the earth, or oil distilled from shales 
which is used, anything which will lessen the run 
on coal and wood fuel will be in favour of the tea 
planters of Ceylon. Here in Ceylon we are not so 
favoured as some of our brethren and competitors in 
India and China are. In both countries constant 
discoveries . are being made of coal, a mineral 
which, it is about as certain as anything can be, 
does not exist in Ceylon. It seems from the 
paper read by Mr. Tarbutt that over and over 
again machinery for consuming oil fuel, tar and 
other residual matter was invented and employed, 
but laid aside with much loss to its projectors, 
in consequence of an immediate and large increase 
in the price of the oils, tar, &c, the moment a 
demand for them set in. But apart from tar and 
the product of shales, the discoveries of natural 
oil of various qualities in America, Batoum, 
Burma, India, and many other places have been so 
numerous and the supplies on so large a scale, that 
we are not surprised to hear of great progress made 
in the use of petroleum oil or its residuum for 
furnaces on shore and afloat, in lieu of coal. This 
wonderful mineral has merits of its own which 
will secure its being largely used, but what we 
desire to see is, so large a use of substitutes as 
will prevent a rise in the price of coal and not 
merely avert increased cost in the case of wood 
fuel but the danger of the exhaustion of supplies 
within easy reach of our tea factories. While on 
this subject we may ask if anthracite coal would 
not be a good fuel for tea factories if it could be 
laid down cheaply enough ? It is largely a natural 
coke. At the opposite extreme is the lignite we 
recently mentioned as likely to reach us from Siam 
and about which we hope som to hear 
further. The cost of transport to any great 
distance is the great difficulty, and if, as we 
were told, it may be possible to lay down from 
Siam at Colombo good quality lignite, fit for use 
in tea factories at B5 per ton, our fuel difficulties 
will very largely disappear. Meantime we cannot 
but watch with interest the enormous stores of 
liquid fuel, ready as distilled by natural action, 
which this old globe of ours is constantly revealing 
for the supply of light and warmth and force, as 
well as the progress of inventions whereby liquid 
fuel is used instead of solid blocks of coal or 
pieces of wood. In the United States there 
are already 9,000 miles of " oleoducts " (pipes 
for conveying petroleum), and a pipe is to be laid 
down between the oil wells on the Caspian and 
the Black Sea, which is to be 600 miles long 
(from Baku to Poti or Batoum), the estimated cost 
being two millions sterling. Our readers may be 
surprised to hear how much of the effect of coal 
is lost each time a furnace is charged with cold 
material, and how great the superiority of petroleum 
oil is in this respect and others of importance. The 
case was thus stated in Mr. Tarbutt's paper: — 
" Turning from the sources of supply to the relative 
values of liquid fuel as compared with coal, we find 
in studying their theoretical evaporative values that 
the beat-producing constituents of different oils vary 
almost as much as those of different descriptions of 
coals, and it is therefore ouly possible (without go- 
ing into a labyrinth of figures) to take a standard 
iu either case, which shall approximate as nearly as 
possible to the average composition of the two fuels. 
The average composition of English, Welsh and 
Scotch coal is then about 80 per cent, carbon, 5 
percent, hydrogen, 8 per cent, oxygen, the remaining 
7 per cent, being nitrogen, sulphur, and ash, which 
for the purposes of this comparison may be dis- 
regarded. The average of the liquid hydrocarbons 
available as fuel may be taken at 87 per cent, carbon. 
12 per cent, hydrogen, and 1 per cent, oxygen. The 
total quantity of heat evolved by the combustion of 
fuel is of course equal to the sum of the heating powers 
of its elements, except that when oxygen is present 
a deduction must be made for the equivalent consti- 
tuent of hydrogen neutralised by it. The heat evolved 
by the combustion of 1 lb. of carbon is 14,500 English 
units, and by 1 lb, of hydrogen 02,000 English units, 
or about 4J times as much. 
"Now in the case of coal a great part of the hydrogen 
is neutralised by the oxygen, being in fact present in 
the fuel in the form of water, whereas iu liquid fuel 
nearly the whole of the hydrogen is uncombined with 
oxygen, and is therefore available for combustion ; and 
it is to this fact that its higher theoretical evapor- 
ative value is mainly due. The value of the two fuels 
is then as follows : — 
Lb. of water evaporated 
English Uaits. per lb. of fuel at aud 
from 212 degrees Fahr. 
Average coal ... 14,000 .. 14-48 
Average liquid fuel 20,000 .. 20'7 
In practice, however, other circumstances in con- 
nection with the methods of combustion of the two 
fuels considerably increase the theoretical difference 
between them. The hydrocarbons in coal, being in 
the solid state absorb a considerable amount of heat 
in volatilising, and, in the ordinary method of haud 
stoking, each time fresh coal is required a large ex- 
cess of air must necessarily be admitted to the fur- 
nace, which has the effect of cooling it down at the 
very moment when the greatest heat is required. 
Mr. D. K. Clark gives the following description of 
what occurs in the furnace when freshly stoked : — 
" A charge of fresh coal thrown on the furnace in 
an active state, so far from augmenting the general 
temperature, becomes at once au absorbent of it, and 
the source of the volatilisation of the bituminous 
portion of the coal — in a word, of the generation 
of the gas. Now, volatilisation is the most cooling 
process of nature, by reason of trie quantity of heat 
which is directly converted from the sensible to the 
latent state. So long as any of the bituminous con- 
stituents remain to be evolved from any atom or 
division of the coal, its solid or carbonaceous part 
remains black, at a comparatively low temperature, 
and utterly inoperative as a heating body. In other 
words, the carbonaceous part has to wait its turn 
for that heat which is essential to iis own com- 
bustion, and in its own particular way. If its bitu- 
minous part be not consumed and turned to account 
it would have been better had it not existed in the 
coal, as such heat would in that case have been 
saved and become available for the business of fur- 
nace. To thi; circumstance may be attributed the 
alleged comparatively greater heating properties of 
coke or anthracite over bituminous coal." 
" In an ordinary coal furnace the temperature is 
subjeitsd to frequent and extreme variations. The 
generation of gas is greatest when the furnace is 
first charged, aud therefore at its lowest tempera- 
ture, and the quantity of air required for the perfect 
combustion of the fuel (which is constantly varying 
as the conditions of the charge vary) is not practic- 
ally ascertainable, nor is it under control. The con- 
sequence is that one of two evils is constantly at 
work — either too much air is being admitted, caus- 
ing smoke and carrying off both fuel and heat up 
the chimney, or else there is not enough air pas- 
sing through the charge to convert the carbon into 
carbonic acid, resulting in the production of large 
volumes of carbonic oxide, which escape uuconsumed 
producing only 4,325 units of heat per lb. of carbon 
instead of 14,500 units, which would be obtained 
were the combustion of the carbon completed. A 
proof of the wasteful manner in which coal is gene- 
rally consumed by steam users was obtained dur- 
ing the investigations made by the corporation of 
Birmingham about two years ago, when a proposi- 
tion^was before them for laying power mains through 
their streets. Non-condensing engines of good type 
work with 2J lb. of coal per gross horse-power per 
hour, but it was found on indicating six engines of 
this class in Birmingham, taken incidentally, and 
