IMPROVEMENTS IN THE TREATMENT OF ASBESTOS FOR PURIFYING THE SAME AND RENDERING IT NON-CORROSIVE IN ITS ACTION UPON IRON
Year: 1883

page_text: LETTERS PATENT to John Dewrance of 158 Great Dover Street Lambeth in
the county of Surrey Engineer for an Invention of IMPROVEMENTS IN THE
TREATMENT OF ASBESTOS FOR PURIFYING THE SAME AND RENDERING IT
NON-CORROSIVE IN ITS ACTION UPON IRON.
PROVISIONAL SPECIFICATION left by the said John Dewrance at the
Office of the Commissioners of Patents on the 17th October 1883.
JOHN DEWRANCE of 158 Great Dover Street Lambeth in the County of Surrey,
Engineer. "IMPROVEMENTS IN THE TREATMENT OF ASBESTOS FOR PURIFYING THE
SAME AND RENDERING IT NON-CORROSIVE IN ITS ACTION UPON IRON
This invention has for its object, certain improvements in the prepartion of
asbestos. It has been found that asbestos as hitherto prepared has a corrosive
action upon iron which greatly limits its use and application.
Asbestos is the form assumed by many minerals of the hornblende-augite group,
such as, Actinolite, Tremolite and Anthophyllite, the white asbestos usually being
a variety of Actinolite, while the darker forms are derived from Tremolite
and Anthophyllite. Hornblende and its analogues are double silicates of the
composition M O Si O,, where M₁ represents one or more of the following
metals Calcium, Magnesium, Manganese Iron and sometimes others of similar
character. In some varieties the silica may be partially replaced by Alumina
(Al, O) or Titanic Acid (Ti O₁) while others have been found to contain small
quantities of fluorine, most probably in the form of a silica-fluoride of calcium or
magnesium. These various forms of asbestos and asbestiform minerals are found
naturally associated with serpentine, talc, steatite, mica, lepidolite, felspar, sodalite,
mica-slate, basalt, gneiss, and other rocks and minerals of volcanic origin and
similar character. Many of these by atmospheric influences become changed, losing
a portion of their alkalies, which become soluble and are carried by water or rain
into the fibres of the asbestos. Thus sodalite is a double silicate often containing
nearly 20% of chloride and sulphate of sodium, and which when acted upon by
water, yield up its soluble salts. Again the asbestos itself is exposed to the

page_text: infiltering action of waters containing chlorides, sulphates, carbonates, silicates,
nitrates &, of sodium, potassium, magnesium-calcium, lithium, iron &°, so that the
asbestos is naturally placed in a favorable position for accumulating these soluble
salts and retaining some of them among its fibres, analyses of many varieties have
shewn that these soluble salts contained in the asbestos are, the sulphates, chlorides
and carbonates of magnesia, lime, sodium, lithum, potassium, together with a little
silica and oxide of iron and perhaps some fluoride of the alkalies or alkaline earths,
and it is to these soluble salts that I attribute the corrosive action which asbestos
has upon iron, and it is well known that saline bodies such as the above, greatly
facilitate the rusting of iron exposed to water containing them in solution.
My improved method of preparing asbestos is to soak it in a dilute solution of
caustic soda, which acts upon the various compounds and renders them very soluble
and readily removable by washing in water, leaving the asbestos pure. Caustic
potash, lime, baryta, strontia, the carbonates of soda and potash and many other
salts would effect the same object, but I prefer caustic soda.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said John Dewrance in the Patent Office on the 17th April 1884.
JOHN DEWRANCE of 158 Great Dover Street Lambeth in the County of Surrey
Engineer IMPROVEMENTS IN THE TREATMENT OF ASBESTOS FOR PURIFYING THE
SAME AND RENDERING IT NON-CORROSIVE IN ITS ACTION UPON IRON."
This invention has for its object certain improvements in the preparation or
treatment of asbestos. It has been found that asbestos as hitherto prepared has a
corrosive action upon iron which greatly limits its use and application-Asbestos is
the form assumed by many minerals of the hornblende-augite group such as
Actinolite, Tremolite and Anthophyllite the white asbestos usually being a variety
of Actinolite while the darker forms are derived from Tremolite and Anthophyllite.
Hornblende and its analogues are double silicates of the composition M O Si Oj
where M represents one or more of the following metals calcium, magnesium,
manganese, iron and sometimes others of similar character. In some varieties the
silica may partially be replaced by Alumina (Al, O₂) or Titanic acid (Ti O,) while
others have been found to contain small quantities of fluorine most probably in the
form of a silico-fluoride of calcium or magnesium. These various forms of asbestos
and asbestiform minerals are found naturally associated with serpentine talc
steatite, mica, lepidolite felspar sodalite mica slate basalt gneiss and other rocks and
minerals of volcanic origin and similar character. Many of these by atmospheric
influences become changed losing a portion of their alkalies which become soluble
and are carried by water or rain into the fibres of the asbestos. Again the Asbestos
itself is exposed to the infiltering action of waters containing chlorides sulphates
carbonates silicates nitrates & of sodium potassium, magnesium, calcium, fithum
iron & so that the asbestos is naturally placed in a favorable position for
accumulating these soluble salts and retaining some of them among its fibres.
I take the crude asbestos in lump and soak it for some days in water-After
having been soaked for some days the asbestos becomes much softer owing to the
water having found its way between the fibres of the asbestos. In this state it is
torn apart or separated by chopping into pieces sufficiently small to go straight into
the mill next hereafter mentioned The Mill which I prefer to use consists of an
ordinary revolving pan and two large revolving wheels and is similar in construction
to an ordinary mortar mill.-Into the pan of this Mill I put a weak solution of
caustic soda e. water containing about 1% of caustic soda, and then cause the
Mill to revolve; I throw in pieces of the asbestos which have been previously
separated and sorted into qualities according to the value of the fibre. I continue
working the Mill until the asbestos has been crushed into fibres of suitable quality.
By this means the asbestos becomes thoroughly soaked in and penetrated by the
caustic soda solution so that after the milling has been performed the asbestos is
ready for washing and can be much more readily cleansed than the asbestos which
has been crushed previous to being soaked in caustic soda
After milling the asbestos is thrown into water and allowed to remain for some
hours, or it may with advantage be boiled in order to dissolve out the soluble salts
and excess of soda. It is then freed from a large quantity of the water containing
the soda and soluble salts by passing it between rollers after which it is again
soaked in water and occasionally stirred up. It is again passed through rollers
and the soaking and rolling repeated two or three times. Finally it is boiled in
distilled or rain water and when passed through the rollers after boiling is ready
for drying when it will be found practically free from any corrosive action on iron.
Caustic potash and other salts may be substituted for the caustic soda in the
process above mentioned but I prefer caustic soda

page_text: Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that I do not
claim the particular means hereinbefore described of scaking the asbestos in the
solution of caustic soda or other substituted material as any other convenient
methods for accomplishing such soaking may be employed but what I do claim as
my invention is the soaking of asbestos in a weak solution of caustic soda or a
substitute for the same and the subsequent washing of the asbestos so soaked
whereby the asbestos is purified and rendered non-corrosive in its action upon iron.
In witness whereof I the said John Dewrance have hereunto set my hand and
seal this sixteenth day of April in the year of our Lord One thousand eight
hundred and eighty four
JOHN DEWRANCE (L.S.)