IMPROVEMENTS IN PRESERVING WOOD
Year: 1878

page_text: LETTERS PATENT to Alexander Melville Clark, of 53, Chancery Lane, in the
County of Middlesex, Patent Agent, for the Invention of " IMPROVEMENTS
IN PRESERVING WOOD." A communication from abroad by Madame Veuve
d'Escalonne, née Caroline Elisabeth Lerevert, of Paris, France,
PROVISIONAL SPECIFICATION left by the said Alexander Melville Clark at
the Office of the Commissioners of Patents on the 8th January 1878.
ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the County of Middlesex,.
Patent Agent. "IMPROVEMENTS IN PRESERVING WOOD." [A communication from
abroad by Madame Veuve d'Escalonne, née Caroline Elisabeth Lerevert, of Paris,
France.]
This Invention consists in the employment of salts of lead for impregnating and
preserving wood. The salts of lead may as a rule be employed either alone or
mixed with other antiseptic matters, such as creosote, phenic acid, tar, &c. The
salts are preferably used alone for impregnating wood, that is to say, without the
aid of any chemical re-agent, forming with them an insoluble precipitate. The salts
of lead which are most adapted for use in the preservation of wood are the plum-
bates of potassa, soda and lime, double hyposulphite of lead and of soda, the
ammonio plumbic salts, the basic acetates and pyrolignites of lead and their
analogues.
In order to fix the soluble compositions of lead in the wood, gaseous re-agents,
such as ammoniacal and sulphurous vapors, vapors of hydrochloric, nitric, and
carbonic acids, &c., may be employed.
The salts last mentioned have been adopted by preference for the following
reasons:-When a soluble salt of lead (acetate, nitrate, &c.,) has been injected into
the wood, and a second injection with a re-agent, such as sulphates, carbonates,
alkalies, &c., susceptible of forming with the salt of lead an insoluble precipitate, is
31

page_text: effected, the second solution can only penetrate the cells of the wood with great
difficulty since the cells are already filled by the liquid first injected, except the
second solution drives out and take the place of the first one, but in either case the
result desired is not attained. Moreover, the precipitates which are formed at
the open extremities of the ligneous fibres obstruct the pores leading to the cells,
so that the liquid is incapable of penetrating any further. For the efficacious
action of a metallic salt it is moreover necessary that it should produce an insoluble
combination with the wood itself, especially with its nitrogenised products. This
combination should also be as rapid as possible to effect a good preservative action.
The best results are obtained therefore by the employment of a soluble salt of lead,
combining easily and rapidly with the resinous matters in the wood, and forming there-
with, without the aid of any other chemical agent, an insoluble and non-putrefactive
combination incorporated with the wood, and not simply enclosed in its cells. The
same means are used as when sulphate of copper is used; when a single liquid is
used, one injection is sufficient.
Among the salts that have been above indicated as the most efficacious, that
which is found most preferable is the basic pyrolignite of lead, by reason of its easy
decomposition in the presence of organic matters, and because it contains fuliginous
or tarry matters which add to the antiseptic qualities of its base.
To obtain this salt, pyroligneous acid is saturated with lead, oxide, or litharge;
when the solution has a freely alkaline reaction the product is dried or diluted with
water to bring the solution to about 1 to 3° Beaumé. In this case the water is
deprived of its earthy salts by means of the ordinary re-agents.

page_text: C
SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Alexander Melville Clark in the Great Seal Patent Office on the
6th July 1878.
ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the County of Middlesex,
Patent Agent. "IMPROVEMENTS IN PRESERVING WOOD." A communication from
abroad by Madame Veuve d'Escalonne, née Caroline Elisabeth Lerevert, of Paris,
France.
This Invention consists in the employment of salts of lead for impregnating and
preserving wood. The salts of lead may as a rule be employed either alone or
mixed with other antiseptic matters, such as creosote, phenic acid, tar, &c. The
salts are preferably used alone for impregnating wood, that is to say, without the
aid of any chemical re-agent forming with them an insoluble precipitate. The salts
of lead which are most adapted for use in the preservation of wood are the plum-
bates of potassa, soda, and lime, double hyposulphite of lead and of soda, the
ammonio plumbic salts, the basic acetates and pyrolignites of lead and their
analogues.
In order to fix the soluble compositions of lead in the wood, gaseous re-agents,
such as ammoniacal and sulphurous vapors, vapors of hydrochloric, nitric, and
carbonic acids, &c., may be employed.
The salts last mentioned have been adopted by preference for the following
reasons: When a soluble salt of lead (acetate, nitrate, &c.) has been injected into
the wood, and a second injection with a re-agent, such as sulphates, carbonates,
alkalies, &c., susceptible of forming with the salt of lead an insoluble precipitate, is
effected, the second solution can only penetrate the cells of the wood with great
difficulty since the cells are already filled by the liquid first injected, except the
second solution drives out and takes the place of the first one, but in either case
the. result desired is not attained. Moreover the precipitates which are formed at
the open extremities of the ligneous fibres obstruct the pores leading to the cells, so
that the liquid is incapable of penetrating any further. For the efficacious action of a
metallic salt it is also necessary that it should produce an insoluble combination with
the wood itself, especially with its nitrogenised products. This combination should
also be as rapid as possible to effect a good preservative action. The best results
are obtained therefore by the employment of a soluble salt of lead combining easily
and rapidly with the resinous matters in the wood, and forming therewith without
the aid of any other chemical agent an insoluble and non-putrefactive combination
incorporated with the wood, and not simply enclosed in its cells. The same means
are used as when sulphate of copper is used; when a single liquid is used one
injection is sufficient.
Among the salts that have been above indicated as the most efficacious, that
which is found most preferable is the basic pyrolignite of lead, by reason of its easy
decomposition in the presence of organic matters, and because it contains fuliginous
or tarry matters which add to the antiseptic qualities in its base.
To obtain this salt, pyroligneous acid is saturated with lead, oxide, or litharge;
when the solution has a freely alkaline reaction the product is dried or diluted with
water to bring the solution to about 1 to 3° Beaumé. In this case the water is
deprived of its earthy salts by means of the ordinary re-agents.
Having described the nature of the said Invention and the manner of performing
the same, I declare that what I claim as the Invention to be protected by the
herein-before in part recited Letters Patent is, the employment for preserving wood
of salts of lead, more especially the plumbates of potassa, soda, and lime, the double
hyposulphite of lead and soda, ammonio plumbic salts, and the basic acetates and

page_text: pyrolignites of lead with or without the addition of tar, creosote, phenic acid, or
other antiseptic matters, as specified.
In witness whereof, I, the said Alexander Melville Clark, have hereunto set
my hand and seal, this Second day of July, in the year of our Lord One
thousand eight hundred and seventy-eight.
A
M
TADI
Gal
A. M. CLARK (LC)