IMPROVEMENTS IN THE MANU- FACTURE OF GAS FOR ILLUMINATING AND HEATING PURPOSES
Year: 1874

page_text: PROVISIONAL SPECIFICATION left by Granville Hamilton Forbes at
the Office of the Commissioners of Patents, with his Petition, on
the 22nd July 1874.
I, GRANVILLE HAMILTON FORBES, of Broughton Rectory, in the
County of Northampton, Clerk in Holy Orders, do hereby declare
the nature of the said Invention for "IMPROVEMENTS IN THE MANU-
FACTURE OF GAS FOR ILLUMINATING AND HEATING PURPOSES," to bo as
follows:-
This Invention relates to improvements upon the Invention for which
Letters Patent, No. 4160, A.D. 1873, were granted to me.
According to my said former Invention I combine chalk with tar or
pitch, or similar bituminous substance, together with a small quantity of
naphtha or petroleum, or other light hydrocarbon oil or spirit, or animal
or vegetable oil, or fat or fatty matter, or a combination of any two or
more of them, which compound I use as a substitute for coal in the
manufacture of gas, or for making quicklime.
According to the first part of my present Invention I improve upon
the foriner Invention by increasing the proportion of naphtha or

page_text: petroleum, or other light hydrocarbon oil or spirit, or vegetable or animal
oil, or fat or fatty matter, or a combination of any two or more of them,
as therein specified. I may use from four to fourteen pints of the above
mentioned oil or spirit, or oil and spirit, to a quarter of a hundredweight
of tar or similar bituminous matter.
According to the second part of my present Invention I combine
chalk with light or volatile tar oil or its equivalent, and tar or similar
bituminous substance, or instead of the above combination I sometimes
employ the following:-I combine the chalk with light or volatile tar
oil, or an equivalent of the same, and tar or similar bituminous matter, 1
with or without a small quantity of naphtha or petroleum, or other
similar hydrocarbon oil or spirit, or animal or vegetable oil, or fat or
fatty matter, or a combination of any two or more of them.
The proportion of the light or volatile tar oil or its equivalent that I
employ will vary considerably. I may use equal parts of the tar oil and 1
tar or similar bituminous substance, or even as much as three parts of
the tar oil to one part of the tar or similar bituminous substanco, or I
may use a smaller proportion of the tar oil or equivalent.
The proportions of the naphtha or petrolcum, or other light hydro-
carbon oil or spirit, or animal or vegetable oil, or fat or fatty matter, 2
will be about the same as those stated in the Specification of the
aforesaid Letters Patent, No. 1160, A.D. 1873.
In carrying my said Invention into practise I proceed in the manner
fully described in the Specification of the above-named Letters Patent.
I combine the chalk with the other specified materials by the process of 2
absorption; I then subject the compound to the process of destructive
distillation in a retort for the manufacture of gas. I may use coal with
the compound or compounds in the retort. Very good results are
obtained by using equal parts of coal and either of these compounds.
I may sometimes vary the proportions as well as the method of 3
procedure in making the compound in the following manner:-Instead
of mixing the naphtha or petroleum, or other light hydrocarbon oil or
fat, or the light or volatile tar oil or equivalent with the tar or similar
bituminous substance before placing the chalk in it, I may place the
chalk in naphtha or petroleum, or other light hydrocarbon oil or spirit, 3
or in light or volatile tar oil, or in a combination of any two or more of
them, and allow it to remain in the liquid until it is saturated with

page_text: the oil or spirit, and then place it in tar or pitch or similar bituminous
substance. The object of this treatment is to cover the chalk with a coating
of bituminous matter, and thus to prevent the evaporation of the oil or
spirit. The chalk should afterwards be allowed to dry in a cool place.
It may-then be again immersed in the tar or pitch or similar bituminous
substance and coated a second time. The tar may first bo boiled, or it
may be mixed with a small quantity of naphtha or petroleum, or similar
light hydrocarbon.