IMPROVEMENTS IN OR RELATING TO THE PROCESS OF DESICCATING OR PRESERVING POTATO AND OTHER KINDRED FOODS OR VEGETABLE SUBSTANCES
Year: 1881

page_text: LETTERS PATENT to George Lister Laird, of Douglas, in the Isle of Man,
for an Invention of "IMPROVEMENTS IN OR RELATING TO THE PROCESS OF
DESICCATING OR PRESERVING POTATO AND OTHER KINDRED FOODS OR
VEGETABLE SUBSTANCES."
PROVISIONAL SPECIFICATION left by the said George Lister Laird at the
Office of the Commissioners of Patents on the 15th February 1881.
GEORGE LISTER LAIRD, of Douglas, in the Isle of Man.
"IMPROVEMENTS IN
OR RELATING TO THE PROCESS OF DESICCATING OR PRESERVING POTATO AND OTHER
KINDRED FOODS OR VEGETABLE SUBSTANCES."
In the manufacture of desiccated potato the prepared potato mash is placed on
perforated shelves in chambers and heated air passed through.. As at present
practised this air is passed through by means of fans sucking out or passing air
in, the pressure being approximately the same as the atmosphere, very slightly
above or below, as the case may be.
I have found however that by keeping a pressure on the air considerably above
that of the atmosphere, and regulating the outlet so as to prevent the pulverulent
matter being carried off by the force of the current, much superior results are
obtained. Much more air can be passed through in a given time, and the drying
is effected in a proportionately shorter period.
An ordinary fan however ceases to be economical if driven at a higher pressure
than one or two inches of water, whereas to gain the effect I require eighteen
inches to three feet of water is the lowest desirable pressure. I therefore, instead
of a fan, employ a blowing engine, such as Root's blower, or the blowing engines
employed in steel works and other places, where any desired pressure can be
applied. To prevent the stuff being blown away by the violence of the blast, as
would be the case without extra precautions, I regulate the exit holes so that the
difference in pressure above the top tray or shelf and below the bottom one shall
not, in ordinary cases, much exceed three quarters of a pound on the square inch,
however high above atmospheric pressure the incoming blast may be; but of course
for different substances the difference in pressure may vary, coarse material allowing
much greater difference than fine. In all cases the exit can be regulated so as to
be narrowed to the point at which the force of the current of air is not sufficient
to carry off the particles of matter being dried.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said George Lister Laird in the Great Seal Patent Office on the 15th
August 1881.
GEORGE LISTER LAIRD, of Douglas, in the Isle of Man.
"IMPROVEMENTS
IN OR RELATING TO THE PROCESS OF DESICCATING OR PRESERVING POTATO AND
OTHER KINDRED FOODS OR VEGETABLE SUBSTANCES."
In the manufacture of desiccated potato the prepared potato mash is placed on
perforated shelves in chambers and heated air passed through.
As at present practised this air is passed through by means of fans sucking out
or passing air in, the pressure being approximately the same as the atmosphere,
very slightly above or below, as the case may be.
I have found however that by keeping a pressure on the air considerably above
that of the atmosphere, and regulating the outlet so as to prevent the pulverulent
matter being carried off by the force of the current, much superior results are
obtained, much more air can be passed through in a given time, and the drying is
effected in a proportionately shorter period.
An ordinary fan however ceases to be economical if driven at a higher pressure
than one or two inclics of water, whereas to gain the effect I require fifteen inches
to three feet of water is the lowest desirable pressure. I therefore, instead of a
fan, employ a blowing engine, such as Root's blower, or the blowing engines
employed in steel works and other places, where any desired pressure can be
applied.
My Invention is better described by aid of the accompanying Drawings, in
which,
Figure 1 is a plan partly in section showing the general arrangement.
Figure 2 is a side elevation of same, also partly in section.
Figure 3 is an end elevation with a section through the furnace.
In these A is the blower (a Root's patent blower is shown as the one I prefer);
B, the furnace; C, the flue; D, the passage for the heated air; E, the chambers or
troughs over which the potatoes to be preserved are placed in trays F; K, the walls
of the building; and L, the chimney.
T'he air forced from the blower through the pipe a into a square pipe or
tube H which runs longitudinally along one side of the furnace, and from thence
into the series of pipes b which traverse the roof and sides of the furnace in the
shape of a horse shoe, and terminate in another longitudinal square tube H. From
the tube H' the air enters the air passage D at a temperature of about 300 degrees
Fahrenheit, from whence it issues by small doors & into the troughs E, over which
the potatoes are placed in perforated trays F. The heated air then passes through
the potatoes, the pressure under which, it is forced causing the complete desiccation
of the potato, and effecting the preserving more effectually and expeditiously than
when the air is simply passed through without force or pressure.
The products of combustion from the furnace B pass along the flue C, which is
separated from the air passage D by a metal plate, thus preserving the heat of the
air until it reaches the troughs E. The sides of the troughs E are preferably built
of single brick, but the bottoms are made much thicker, of concrete, and covered
with cement to allow of their being thoroughly cleaned and washed. The trays F
are of perforated metal or gauze wire, which offer but little resistance to the force
of the air, allowing the full pressure to operate upon the potatoes. (These trays are
only shown in position on one trough in the Drawings.)
To prevent the stuff being blown away by the violence of the blast, as would be
the case without extra precautions, I prefer to regulate the blast by any suitable

page_text: governing apparatus; but in some cases it may be found desirable, instead or in
addition to regulate the exit holes so that the difference in pressure above and
below the tray or shelf shall not much exceed half a pound on the square inch,
however high above atmospheric pressure the incoming blast may be; but of course
for different substances the difference in pressure may vary, coarse material allowing
much greater difference than fine. In all cases the exit can be regulated so as to
be narrowed to the point at which the force of the current of air is not sufficient to
carry off the particles of matter being dried. Where however work people are, as
in my factory, continually coming in and going out of the chamber, the plan or
regulating the blast alone must be employed.
The advantages of my process are not merely a saving in time through the much
quicker drying under a powerful current and large volume of heated air, but an
actual improvement in the manufactured article, as while under the gentle current
hitherto used the flocula lies nearly dead, or merely cakes or shrinks as it gives oft
its moisture, my flocula is much more honey-combed by the first drying, is
afterwards kept continually vibrating by the air, thus better exposing the particle
to the current, and forming a more puffy or floculent material when dry, which
material dissolves more easily in water than the ordinary article. Further, I find
by my new process the great difficulty in the old one of preventing scorching from
undue heat at starting is easily avoided, as from the strong blast passing through
the heating pipes the air has not time to arrive at too great a heat.
Having now described my Invention, and the best mode known to me of carrying
it into effect, I wish it to be understood that I do not claim broadly the process of
desiccating potatoes by means of heated air, but that what I believe to be new
and desire to protect under the herein before in part recited Letters Patent is,-
The process of desiccating or preserving potato and other kindred foods by
passing through the prepared mash a current of heated air at a pressure con-
siderably above the atmospheric obtained by means of a blower, blowing engine, or
other equivalent mechanism delivering a regulated current of uniform pressure
through the apparatus, substantially as described.
In witness whereof, I, the said George Lister Laird, have hereunto set my
hand and seal, this Tenth day of August, in the year of our Lord One
thousand eight hundred and eighty one.
5 Witness,
WM
P. THOMPSON,
Patent Agent,
Liverpool and London.
GEORGE LISTER LAIRD. (L.S.)