Year: 1886

page_text: We, NILS ALEXANDER ALEXANDERSON, and LEONARD HVASS, of Stockholm, in
the Kingdom of Sweden, Engineers, do hereby declare the nature of this inven-
tion and in what manner the same is to be performed, to be particularly described
and ascertained in and by the following statement:-
This invention relates to an improved mode or method of tawing hides and skins,
by means of which leather is produced which does not become brittle, and under
the influence of water, lose its nature, as is frequently the case with hides or skins
which are tawed according to the methods heretofore employed.
The improved method is practised in substantially the following manner, that is
to say-The hides or skins, after having been subjected to the ordinary preparatory
operations, such as soaking, unhairing and swelling, are placed in a strongly basic
solution of salts of alumina, oxide of chromium, or oxide of iron prepared in the
manner hereinafter described, in which solution they are left until the fibres of
the hides or skins have absorbed a sufficient quantity of the active principle of these
substances; after which the hides or skins are treated with water.
Owing to the property of the latter to decompose the sesqui oxide salts, and the
affinity of the fibrous matter for the oxides of the former, indissoluble hydrate of
alumina, or corresponding hydrate of the other oxides deposits upon the fibres;
the dissoluble salts are removed by subsequent treatment with water.
The hides or skins are subsequently dried and subjected to the treatment usually
adopted in tawing, in order to soften and finish them.
It will thus be understood that the utilization of the property of hides and skins
to cause the deposition thereon of the oxyhydrates contained in the basic sesqui-
oxide salts, the property of water to decompose the said salts, and the subsequent
washing off of the soluble salts constitute the characteristic features of this improved
method which distinguish it from former methods of tawing where it is the acid
and consequently corrosive properties of the salts introduced in the fibres which
cause the inconveniences herein before referred to.
If mechanical pressure, kneading, stirring and the like are employed, the pene-
tration of the basic solution and the water into the hides or skins is facilitated,
whereby the time necessary for performing the operation is reduced.
The solution of sesquioxide salts employed in tawing according to our method
is prepared in the following manner, that is to say :-To a solution of alumina or

page_text: other sesquioxide salt is added a diluted alkaline solution until complete neutraliza-
tion is effected, or until indissoluble deposit begins to appear. The solution obtained
in this manner is diluted to a suitable strength, and is then ready for use in treating
hides and skins as above described.
In lieu of treating a hide with a basic salt solution, a neutral or acid solution
may in certain cases be employed, the hide being subsequently treated with an
alkaline solution, or vice versa.
Leather prepared in this manner will not become brittle, as the oxyhydrate not
soluble in water and deposited upon the fibres has not the acid and corrosive
properties of the soluble salts; it possesses moreover a high degree of resistance
against water and will not be attacked by moths.
Having now particularly described and ascertained the nature of our said
invention, and in what manner the same is to be performed, we declare that
what we claim is :-
The method herein before described, the characteristic features of which consist
in causing the oxyhydrates contained in a basic solution of sesquioxide salts to be
deposited upon the fibres of the hides or skins, and subsequently washing off the
soluble matters, for the purpose specified.