AN IMPROVED FILTERING BLOCK
Year: 1879

page_text: LETTERS PATENT to Charles Heisch, of Mark Lane, in the City of London,
Analytical Chemist, for the Invention of "AN IMPROVED FILTERING BLOCK."
PROVISIONAL SPECIFICATION left by the said Charles Heisch at the Office
of the Commissioners of Patents on the 13th May 1879.
CHARLES HEISCH, of Mark Lane, in the City of London, Analytical Chemist.
"AN IMPROVED FILTERING BLOCK."
My Invention consists in making an improved filtering block or slab of a mixture
of pumice stone and carbon, effected by mixing the former with pitch and tar, and
burning after moulding.
The process of manufacture to which I now give preference is,-
Firstly. To crush or grind the pumice, preferably in a mill similar to a coffee
mill (the pumice being first broken into small pieces fit to go into the mill). I then
sift off all dust which will pass through a sieve of 100 to the inch.
The coarse powder which remains on the sieve is what I employ.
I then warm, in a suitable vessel, either coal tar or Stockholm tar, preferably the
former, and dissolve in it a certain amount of pitch. When completely dissolved I
permit the mixture to cool till it is of the consistence of thick syrup, and I then
stir in the ground pumice. When well mixed, and almost cold, the mixture, which
is now in the form of a coarse, damp powder, is put into an iron or other suitable
mould of the size and shape of the block required, and strongly pressed, either in a
screw press, or by bammering or any other convenient means.
When removed from the moulds the blocks or slabs are placed in crucibles or
saggers, and covered completely with powdered coke, charcoal, or other suitable
substance, to exclude the air, and are then burnt in a reverberatory or other suit-
able furnace till all volatile matters are driven off. When cold, the blocks are
removed from the saggers, cleansed from the powdered coke, and are then fit for
use.

page_text: I do not propose to confine myself to any particular proportions of the different
ingredients, but I prefer the following, which answer well :-
Ground pumice
Pitch
Tar
-
43 lbs.
11 lbs.
2 gls. (weight about 32 lbs.).
Of this mixture I use at the rate of 1.33 ozs. per each cubic inch of the block
required, and press to the right size.
1 may sometimes add some powdered wood or animal charcoal as well as the
pumice, and I may not always press to quite the same extent; but I find the above
work well.

page_text: November 1879.
CHARLES HEISCH, of Mark Lane, in the City of London, Analytical Chemist.
"AN IMPROVED FILTERING BLOCK."
My Invention consists in making an improved filtering block or slab of a mixture
of pumice stone and carbon, effected by mixing the former with pitch and tar, and
burning after moulding.
The process of manufacture which I adopt is as follows:-
:-
I crush or grind the pumice in a mill similar to a coffee mill, or in any mill or
apparatus which I may find suitable, the pumice being first broken into pieces fit to
go therein.
I then pass the pumice through suitable sieves, accordingly as I may require a
finer or a coarser powder for the filtering blocks to be made.
For ordinary filtering blocks I pass the pumice firstly through a sieve of, say,
twenty holes to the inch, and afterwards sift off all the dust which will pass through
a sieve of, say, fifty holes to the inch; the coarse powder which remains in this last
sieve is what I employ.
I then warm, in a suitable vessel, either coal tar or Stockholm tar, preferably the
former, and dissolve in it a certain amount of pitch. When completely dissolved I
permit the mixture to cool until it is of the consistence of thick syrup, and I then
stir in the ground pumice. When well mixed, and almost cold, the mixture, which
is now in the form of a coarse, damp powder, is put into an iron or other suitable
mould of the size and shape of the block required, and strongly pressed, either in a
screw press, by hammering, or by any other convenient means.
When removed from the moulds I place the blocks or slabs in crucibles or saggars,
and cover them completely with powdered coke, charcoal, or other suitable sub-
stance, to exclude the air: I then burn them in a reverberatory or other suitable
furnace until all volatile matters are driven off. When cold I remove the blocks
from the saggars, cleanse them from the powdered coke, and they are then fit for
use.
I do not confine myself to any particular proportions of the different ingredients
entering into the composition of my improved filtering block, but I find the following
to answer well:-
--
Ground pumice
Pitch
Tar
54 lbs.
11 lbs.
21 gallons (weight about 321/, lbs.).
Of this mixture I use at the rate of about 1.33 ounces for each cubic inch of the
block required, and press to the right size.
I may sometimes add some powdered wood or animal charcoal in the composition
of my improved filtering block, and I may not always press to the same extent.
The shape and dimensions of the blocks or slabs may, of course, be varied according
to requirement.
Having now described and ascertained the nature of my said Invention, and in
what manner the same is or may be performed, I desire it to be understood that I

page_text: I claim as secured to me by the herein-before in part recited Letters Patent is,--
The use of granulated pumice stone in the composition of a filtering block, sub-
stantially as herein-before described.
In witness whereof, I, the said Charles Heisch, have hereunto set my hand and
seal, this Eleventh day of November, in the year of our Lord One thousand
eight hundred and seventy nine
Witness,
E. H. WATERWERTH,
147, Houndsditch.
CHA. HEISCH. (LS.)