64 
POPULAR SCIENCE REVIEW. 
most perfect coal-gas, which is, indeed, self-produced as it is 
wanted, without any costly or complicated apparatus, and in a 
state of purity unattainable by ordinary means. 
Intermediate between olefiant gas and the solid paraffin in 
condensation, but of the same per-centage composition, are a 
variety of other bodies which assume the form of oils more or 
less volatile in proportion to the number of atoms which are 
compressed into the same bulk. They are known by the name 
of paraffin oils, and their inflammability, volatility, and con- 
sequent danger, when used as household illuminants, increase 
as they approach in rarity the gaseous extremity of the scale, 
and diminish as they draw near the density of the solid. 
True paraffin oils must be carefully distinguished from spurious 
bodies of the same name •* these contain various volatile bodies, 
the vapours of which take fire at the ordinary temperature, and 
which are as dangerous as common turpentine or benzol on 
the approach of a light. True paraffin oil vail only burn in the 
presence of a wick, and is, therefore, perfectly safe. When 
burning, it also splits up into olefiant gas, and, therefore, pro- 
duces a brilliantly-white light. 
We stated at the commencement of this article that some of 
the products of the distillation of coal were acid bodies. The 
most important of these is carbolic acid, which is one of the 
principal constituents of creosote. This has recently been em- 
ployed for sanitary purposes. Its antiseptic properties are 
remarkable, and when united with lime, it forms one of the 
most powerful disinfectants known. Carbolic acid is now pre- 
pared in enormous quantities from coal-tar, and has been 
applied with eminent success in several towns to the disin- 
fection of sewage. It acts, not by destroying putrefactive 
principles as chlorine does, but it completely arrests decom- 
position. Animal matter washed over with a solution of this 
acid may be exposed for any length of time to the atmosphere 
without putrefying ; and Dr. Lyon Playfair mentions an 
instance in which a human body was preserved for two months 
in this way until it reached a distant grave. 
When carbolic acid is acted upon by nitric acid a somewhat 
similar effect is produced as with benzol under these circum- 
stances ; part of the hydrogen is replaced by peroxide of nitro- 
gen, and a body known as carbazotic acid is produced. Within 
the last few years this body has been extensively employed as 
a dye. The colour which it communicates to silk or wool is of 
* Nor must they he confounded with petroleum oil, which is now being 
imported largely from Canada and Pennsylvania. This substance will cause 
a great revolution in our modes of illumination, especially amongst the poor. 
It will be treated in a special article. — Ed. 
