; 81 
for candles. Paraffin is a mixture of neutral bodies containing 
no oxygen, but about 85 per cent. of carbon, and 15 per cent. of 
hydrogen. Its consituents, as also of the other products of this 
distillation, are fatty hydrides, with an almost entire absence 
of ‘‘aromatic hydrides.” This fatty series of hydrocarbons 
(C,H ., + 2) has for its first member marsh gas (CH,); and con- 
tains a large number of homologous bodies, some of which are 
gaseous, some liquid, and some solid, at the ordinary tempera- 
ture. These bodies form the starting point of a large number of 
derivatives, which are very different in character from those derived 
from the ‘‘aromatic hydrides.” The latter can, however, be 
obtained from the former by suitable actions. The composition 
of American natural oil, or petroleum, is essentially the same 
as the artificial or paraffin oils. Russian petroleum contains, in 
addition to the paraffin series, a considerable portion of ‘‘aromatic 
hydrocarbons.” 
Having seen somewhat the working of a low-temperature 
industry, let us turn to the most important example of high- 
temperature distillation—viz., the manufacture of illuminating 
gasfrom coal. The process is conducted very much as follows:— 
Coal is heated in fire-clay retorts set in a horizontal position, 
usually in a group of five or seven. The heat is supplied from a 
furnace, placed in the base of the setting, fed by coke. 
The temperature maintained in the retorts is usually a 
bright or orange red, and is 2000° to 2200° Fahr. A compara- 
tively low heat means a small yield of gas, which is, however, 
generally of a good quality; and the production of a large 
quantity of tar, which is of inferior quality, being rich in 
paraffins but poor in the valuable ‘‘ aromatic compounds.” 
The following tables show the effect of temperature on the 
quantity and quality of the gas produced,* as observed by Mr. 
Lewis T. Wright, F.C.S., Assoc. M. Inst. C.E. :— 
Heat. Cubic Feet Mluminating 
5 Per Ton of Coal. Power. 
(fyeDall red i. a tebtoeeews bows 8,250 3¢ 20°50 
(2): Bright-reditSavtee Goecdae dss 9,693 i 17°80 
(3) Dull orange .............. 10,821 a6 16°75 
(4) Bright orange ...........- 12,006 as 15°60 
Analyses of Gases produced. 
By Volume. No.1. No. 2. No. 4. 
iydrogen 3.00. seco 38°09"... 43°77 «..  SA8 02 
Carbonic oxide ........ S272) See A250h S., s-06 
Marsh gas ...:........ AMT2 a .  B450, » 22. 30:70 
Olehinesy . sas.s0.e:. snes WEB O =o are 5:85) ae 4:51 
INTMOP ER). « jors0:5.00 tae 7g Oe 3°40... 2°81 
100-00 100-00 100-00 
Carbon density of olefines 2°73 .. CA ae 2-62 
Hydrogen ,, Pe ee 3°84, ZA Ee ee 5°76 
___* These are taken from a paper, on “The Influence of the Temperature of Dis- 
tillation on the Composition of Coal Gas,” published in the Jowrnal of Gas Lighting 
for March 25, 1884 (p. 535). ; 
NS POON Se re a i PM OS Oe en En Pe, a Se ee Bs eae 
