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proportion of water may be used but, in that
event, a corresponding additional burden
would be imposed upon the drying appara-
tus employed in the next stage of the manu-
6 facture. The dampened mass of starch,
homogeneously admixed with the solution of
oxalic acid, is next introduced into a rotary.
vacuum drier, which is preferred for the
reason that it insures the uniform conduct
10 of the process during this period, and par-
ticularly because it permits the speeding up
of the drying operation, at a temperature
which is safely below the limits of the tem-
perature which would break up the starch
15 granules and convert the mass into a paste.
The rotary vacuum drier that we prefer for
the purpose would be provided with a steam
. jacket, which may conveniently be supplied
with steam at say 20 lbs. superatmospheric
20 pressure, corresponding to a temperature of
about 259 F. Within the vacuum drier, we
prefer to maintain a vacuum of say 20
inches, so that the internal temperature, dur-
ing the drying operation shall be corre-
25 spondingly restricted well below the limit of
the breaking up of the starch granules. It
is found that at the termination of a period
varying somewhat with the prevailing con-
ditions, but usually about one and- one half
30 hours, and while the drier is rotating at an
average speed of from five to six revolutions
per minute, the water of solution has been
practically expelled, leaving the starch with
about its original content of -moisture, say
35 from 9 to 11% by weight. Under the con-
tinued action of the heat, the oxalic acid
exerts a continued modifying action upon
the starch, and, at this stage of the opera-
tion, extreme care must be taken to supervise
40 and test its progress, so that it -may neither
fall short of nor exceed the limits necessary
for the ultimate result. To this end, from
time to time, the rotation of the.drier is in-
terrupted and a sample of the contents is
45 taken and quickly tested for viscosity. A
suitable viscosity test which we have used
with successful results consists in comparing
the rate of flow of a standard solution of the
test sample, neutralized and boiled, as here-
50 inafter specified, with the rate of flow of
water through a burette, having a length of
36. inches and an internal diameter of )ths
of an inch and delivering 58 c. c. of water in
a period of half a minute. To 100 grams of
55 the.dry starch is first added 400 grams of
cold water. The water and starch are stirred
well together and then is added sufficient
ammonia of 260 Baum to make the solution
alkalin. The mixture is then heated to be-
0 tween 185* F. and 1900 F. thereby breaking
up the starch granules. Then enough cold
water is added to produce a volume of about
970 c. c. of the mixture at a temperature of
100.* F. In the meantime, the burette has
65 been brought to 'the same temperature and'the burette is filled- with the solution and its
rate of flow tested.. When the test of any
particular sample, (with due allowance for
the time occupied by the making of the test)
indicates that the starch in the drum will re- 70
spond to a' viscosity ranging from 40 c c. to
45 c. c. in half a minute from the burette em-
ployed, the rotation of the drum is inter-
rupted and its contents are immediately dis-
charged into a second mixing apparatus con- 75
taining 40 lbs. of 260 ammonia in 200 lbs.
.of water. The mass is at once vigorously
stirred, so as to interrupt the modifying tc-
tion .by - thoroughly neutralizing the acid.
Thereupon, the neutralized mass of modified 80
starch is dried in any convenient manner as,
for instance, by being placed in shallow
trays and heated in a drying tunnel or the -
like. It will usually be found desirable, be-
fore placing the neutralized mass in the 85
trays to pass it through a breaker for the
purpose of breaking up any lumps that may .
have formed, so that the drying operation
may proceed with corresponding promptness
and uniformity. It is unnecessary to take 90
special precautions during the drying of the
neutralized mass, inasmuch as there will be
no prejudicial changes in the desired char-
acteristics of the modified starch after it has
reached this stage of the operation. 95
In order to make up the composition em-
ployed for the coating of lithographer's pa-
per, a' suitable mineral base may be em-
ployed, as, for instance, kaolin, blanc fixe,
satin white, etc. In the case of kaolin, 100 100
lbs. may be employed intimately mixed
with 50 lbs. of water. 25 lbs. of the dry
modified starch produced in accordance
with the method hereinbefore described is
then intimately mixed with 100 lbs. of cold 105
water and the mixture is heated to a tem-
perature such that the starch granules will
be broken up, a temperature of about 185*
F. to 1900 F. ordinarily sufficing for the
purpose. The starch product thus obtained 110
i' then mixed with the kaolin and water un-
til the whole is in a homogeneous union.
The mixture is then strained and is ready
for the paper coater, who may use addi-
tional water for thinning down purposes, 115
according to the particular character of
coating which he wishes to produce for the
purpose at hand.
When, for special reasons, it is desired to
make use of 'the. fundamental features of 120
our invention, for the production of a com-
position to be immediately applied to the
paper, we may proceed directly with the
production of the coating without produc-
ing the modified starch in a dry state. In 125
accordance with this practice, we prefer to
introduce the starch and the oxalic acid, in
the same relative quantities in a volume of
water sufficient to bring the starch into sus-
pension, and to then heat the mixture suffi- 13
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Dunham, Andrew A. & Dunham, Henry V. Adhesive and Method of Making the Same, patent, February 18, 1913; [Washington D.C.]. (https://texashistory.unt.edu/ark:/67531/metapth510456/m1/2/: accessed June 11, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu; crediting UNT Libraries Government Documents Department.