IMPROVEMENTS IN THE MANUFACTURE OF PORTLAND CEMENT
Year: 1879

page_text: LETTERS PATENT to John Watson, of Gateshead, in the County of Durham,
for the Invention of "IMPROVEMENTS IN THE MANUFACTURE OF PORTLAND
CEMENT."
Sealed the 8th August 1879, and dated the 17th April 1879.
PROVISIONAL SPECIFICATION left by the said John Watson at the Office
of the Commissioners of Patents on the 17th April 1879.
JOHN WATSON; of Gateshead, in the County of Durham.
MANUFACTURE OF PORTLAND CEMENT."
"IMPROVEMENTS IN THE
My Invention relates to improvements in the manufacture of Portland cement,
whereby considerable economy in the cost of its production is effected, whilst at
the same time its quality is equal or superior to that of the cement made according
to the ordinary method.
In carrying out my Invention I employ as the ingredients of which the cement
is composed the residual products or slag obtained from blast furnaces, to which I
add raw chalk or clay, or both, or other suitable materials if the chemical analysis
and consistency of the slag employed require it. 1 either procure the slag in the
condition of powder from blast furnaces, the residual products of which naturally
assumes a powdered or granulated form; or I take the slag obtained from other
blast furnaces and reduce it to a fine state of division by mechanical means. I then
mix with the slag when in this condition (before calcination) the raw chalk, clay,
or other additional materials (if necessary to be employed), and subject the whole
to washing, drying, calcining, and grinding by any ordinary or suitable processes.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said John Watson in the Great Seal Patent Office on the 27th September
1879.
JOHN WATSON, of Gateshead, in the County of Durham. " IMPROVEMENTS IN THE
MANUFACTURE OF PORTLAND CEMENT."
My said Invention relates to improvements in the manufacture of Portland
cement, whereby considerable economy in the cost of its production is effected,
whilst at the same time its quality is equal or superior to that of the cement made
. according to the ordinary method.
In carrying out my said Invention I employ as the ingredients of which the
cement is composed the residual products or slag obtained from blast furnaces, to
which I add raw chalk and clay. I either procure the slag in the condition of
powder from blast furnaces, the residual products of which naturally assume a
powdered or granular form; or I take the slag obtained from other blast furnaces
and reduce it to a fine state of division by mechanical or other woll known means.
I then mix with the slag when in this condition the raw chalk and clay, and subject
the whole to washing, drying, calcining, and grinding by any ordinary or suitable
processes.
The proportions in which the several ingredients are employed will vary
according to the chemical analysis of the slag.
In the case of slag containing an approximately maximum quantity of lime and
an approximately minimum quantity of silica and alumina, say, for example, in
one hundred parts of slag, about sixty per cont. of lime, and about ten per cent. of
alumina, with about thirty per cent. of silica, I have found the following proportions
of clay, chalk, and slag to give good results in practice, videlicet :-
Clay about two parts by weight.
Chalk about five parts by weight.
Slag about two parts by weight.
In the case of slag containing an approximately minimum quantity of lime and
an approximately maximum quantity of silica and alumina, say, for example, in
one hundred parts of slag about thirty four per cent. of lime, and about thirty
two per cent. of alumina, with about 34 per cent. of silica, the relative pro-
portion of chalk used should be increased in order to supply the deficiency in the
lime, and the relative proportion of the slag used should be reduced so as to avoid
excess of silica and alumina. . I have usually found in such cases the following
proportions to give good results in practice, videlicet :-
Clay two parts by weight.
Chalk seven parts by weight.
Slag 1'/, parts by weight.
I do not however confine myself to the precise proportions given, as a slight
deviation from them will not materially affect the quality of the cement, although I
have found the proportions indicated to be most suitable for the respective kinds of
slag used.
From these two approximately extreme cases chemists conversant with the
manufacture and the essential properties of Portland cement will be readily able to
vary the proportions of the several ingredients in any intermediate cases, according
as the analysis of the particular slag selected may indicate to be necessary.
Having now described and particularly ascertained the nature of my said In-

page_text: and therefore claim as the Invention secured to me by the hereinbefore in part
recited Letters Patent is,-
The manufacture of Portland cement by the employment of slag, chalk, and clay
in conjunction, substantially as herein before described.
In witness whereof, I, the said John Watson, have to this my Specification
set my hand and seal, the Seventeenth day of September, One thousand
eight hundred and seventy nine.
JOHN WATSON. (L.S.)