IMPROVEMENTS IN THE TREATMENT OF CARBONATE OF LIME FOR THE PREPARATION OF PIGMENTS. THEREFROM, AND IN THE APPARATUS EMPLOYED THEREIN
Year: 1868

page_text: PROVISIONAL SPECIFICATION left by John Henry Johnson at the
Office of the Commissioners of Patents, with his Petition, on the
6th November 1868.-A communication from abroad by Charles
Jules de Bras de Fer, of Paris, in the Empire of France, Com-
mander of the Legion of Honour.
I, JOHN HENRY JOHNSON, of 47, Lincoln's Inn Fields, in the County
of Middlesex, Gentleman, do hereby declare the nature of the said
Invention for "IMPROVEMENTS IN THE TREATMENT OF CARBONATE OF LIME FOR
THE PREPARATION OF PIGMENTS. THEREFROM, AND IN THE APPARATUS EMPLOYED
THEREIN," a communication from abroad by Charles Jules de Bras de
Fer, of Paris, in the Empire of France, Commander of the Legion
of Honour, to be as follows:-
This Invention relates to a peculiar mode of and apparatus for purifying
chalk or carbonate of lime with a view to the preparation therefrom of
a white powder to be used in pigments as a substitute for white lead, the

page_text: improved pigment to which the Inventor gives the name of "Neóblanc"
being not only much cheaper than white lead but perfectly innoxious.
According to this Invention the purification or removal of solid
foreign matters from the carbonate of lime is effected by sifting the
carbonate whilst in a perfectly anhydrous state in apparatus specially
adapted for the purpose. One form of apparatus which will be found
to answer well in practice consists of two concentric polygonal screens
placed at a slight inclination and attached to a central longitudinal shaft
to which rotatory motion is imparted by a strap and pulley, or otherwise,
the screens being enclosed in a tight casing of wood or metal. The
inner screen which projects beyond the outer one at the delivery end is
composed of wire gauze, and the outer one of fine testile fabric and
along the arms which carry these screens are sliding weights which as
the arms revolve alternately fall from and towards the centre, thereby
giving a succession of shocks or blows to the screens, which have the
effect of shaking off any fine particles which may be adhering thereto.
A further shaking motion is transmitted to the shaft carrying the
ser cens by fixing a ratchet wheel thereon, the teeth of which revolve
in contact with a fixed pin. The chalk or carbonate of lime in a
perfectly dry state, but containing all the impurities it retained when
first taken from the chalk pit, is placed in a feeding hopper on the top
of the casing, and as it descends it passes between a pair of grooved
rollers rotating at different speeds, which have the effect of crushing
down the lumps. These rollers are prevented from clogging by fixed
combs or scrapers adjusted beneath them. The crushed material is then
conveyed by a horizontal archimedian screws to a vertical spout, the
lower end of which is forked and enters the interior of the inner screen.
As the material progresses, along the screen it receives a first sifting,
that which passes thro' the meshes of the inner screen falling upon the
finer surface of the outer screen, where it is further screened, those
impurities which are too large to pass the inner screen being discharged
through the open mouth at its lower end. It will thus be seen that
various degrees of fineness will be obtained, which are collected in
separate compartments. The dust or impalpable powder which floats
about the interior of the casing is collected on moveable shelves for the
purpose, from which it is removed at suitable intervals, and constitutes
the finest of all the screened products.
The degree of whiteness of the pigment prepared from carbonate of

page_text: lime thus sifted may be varied according to taste by the addition thereto
in various proportions as may be required of either extra fine flowers or
oxide of zinc freed from noxious substances or guimet blue also of extra
fineness.