A NEW AND IMPROVED METHOD OF GRANULATING MILLSTONES
Year: 1878

page_text: LETTERS PATENT to John Whittier Throop, of 5, Aldersgate Street, in the
City of London, for the Invention of "A NEW AND IMPROVED METHOD OF
GRANULATING MILLSTONES." A communication from abroad by Edward P.
Welch, James H. Welch, Rosia W. Welch, Charles Reed, James P. Willett,
and Edmund P. Hann, trading as Welch Brothers and Company, of George-
town. D.C.. United States of America.
PROVISIONAL SPECIFICATION left by the said John Whittier Throop at
the Office of the Commissioners of Patents on the 30th September 1878.
JOHN WHITTIER THROOP, of 5, Aldersgate Street, in the City of London. "A NEW
AND IMPROVED METHOD OF GRANULATING MILLSTONES." A communication from
abroad by Edward P. Welch, James H. Welch, Rosia W. Welch, Charles Reed,
James P. Willet, and Edward P. Hann, trading as Welch Brothers and Company,
of Georgetown, D.C., United States of America.
The nature of this Invention consists in the application of fluoric acid to the
grinding surfaces of millstones for the purpose of cleansing them of "glaze," and at
the same time opening the pores or granulations of same as will be herein-after set
forth.
• To enable others to use this Invention I will proceed to describe my mode of
manipulation.
The stones are first placed in horizontal position face upward, and after being
dusted (or washed if necessary) fluoric acid, fluoride of ammonia, or its equivalent,
or any compound having fluoric acid in active form is used as a coating for the
entire face.
After the acid has remained upon the stone a sufficient length of time to remove
the "glaze," it is washed off with water and the stone is ready for use.
It will then be found that not only is the "glaze" removed, but the granulations
of the stone will appear in perfect condition for work, and that without the use of a
pick or other instrument.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said John Whittier Throop in the Great Seal Patent Office on the 24th
March 1879.
JOHN WHITTIER THROOP, of 5, Aldersgate Street, in the City of London. "A NEW
AND IMPROVED METHOD OF GRANULATING MILLSTONES." A communication from
abroad by Edward P. Welch, James H. Welch, Rosia W. Welch, Charles Reed,
James P. Willett, and Edmund P. Hann, trading as Welch Brothers and Company,
of Georgetown, D.C., United States of America.
It is well known to millers that buhr and other millstones after being used
become dulled or glazed and have to be sharpened.
The usual mode of sharpening is by dressing the surface with suitable cutting
tools, so as to expose a fresh and properly granulated surface.
This is an expensive method, and the stones when first treated are rather too
sharp. It has been attempted to remove the glaze by alkaline or acid washes, but
these give only imperfect results.
This Invention is based on the discovery that hydrofluoric acid, sometimes called
fluoric acid, and also certain of its compounds will remove the glaze, and also
give the properly granulated surface to the stone, such as is required to give the
best results in grinding.
The surface is by this treatment in a better condition than it could be made by
any of the known mechanical methods.
To enable others to use this Invention I will proceed to describe the mode of
manipulation.
The stones are first placed in horizontal position face upward, and after being
dusted or washed if necessary, hydrofluoric acid is used as a coating for the entire
face. After the acid has remained upon the stone a sufficient length of time to
remove the glaze it is washed off with water and the stone is ready for use.
I generally apply the acid on the stone at different points, and then take a brush
and spread it over the entire surface of the same. It is then allowed to remain
from thirty to fifty minutes, according to the kind and condition of the stone. The
ordinary commercial acid will serve my purpose.
The glaze it will be found is not only removed, but the granulations of the stone
will appear in perfect condition for work, and that without the use of a pick or
other instrument.
I may use ammonia with fluoric acid or ammonium fluoride, or I may use other
combinations with fluoric acid as an element.
I do not claim to be the discoverer of the properties of hydrofluoric acid of
corroding and etching glass, stone, and other siliceous substances, as this has been
long known.
I am also aware that fluoric acid has been used for cutting grooves in millstones,
but I am not aware that my improved process has ever before been used, whereby
the entire grinding surface of a millstone has been cleansed and sharpened and the
pores of the stone opened, and the entire surface of the stone thereby placed in a
condition to operate perfectly without the use of a mechanical millstone dresser.
Having now fully described and ascertained the nature of the Invention com-
municated to me as aforesaid, what-
I claim as new and as secured to me by the herein-before in part recited Letters
Patent is,-
Firstly. The above-described mode of cleansing millstones with hydrofluoric acid,
substantially as set forth.

page_text: Secondly. For cleansing millstones, hydrofluoric acid in any of its compounds,
for the purpose as set forth.
In witness whereof, I, the said John Whittier Throop, have hereunto set
my hand and seal, this Fifteenth day of March, in the year of our Lord
One thousand eight hundred and seventy-nine.
JOHN WHITTIER THROOP. (L.S.)