O I 
operation. Thefe rollers are made of caft-iron, and truly 
turned in a lathe,.their fpindles running in brafs bullies, 
fixed in iron frames bolted down to the wood-work. 
Thefe frames have mortifes in the n, in which the bulhes 
for the pivots-of the roller g are placed, with liberty to 
Aide in the mortifes when they are pufhed up by (crews 
(crewed through the ends of the iron frames. By thefe 
means, the rollers can be fet at any diftance apart, accor¬ 
ding to the (ize of the feed which is to be crufhed be¬ 
tween them ; 1 , 1 , are two (mall iron cog-wheels, of fifteen 
teeth each, fitted on the ends of the pivots of the rollers ; 
they make both rollers turn together with the lame mo¬ 
tion : the feed is put into a hopper, fupported at fome 
diftance above the roller, and it runs out at an opening 
in the bottom into a trough called the (hoe, which is con¬ 
tinually (liaken, by means of a piece of wood nailed to it, 
reding upon the cog-wheel l. By this means, the (hoe con¬ 
tinually feeds the rollers with a (mall quantity of feed, 
without any danger of choaking them up ; and the feeds 
fall, from the end of the (hoe, between the rollers, which, 
as they turn round, take the feed in between them, and 
bruife it. It is proper to have a piece of iron plate nailed 
to fome part of the frame, and kept conftantly prefting 
againft the rollers, fo as to fcrape off the feed which may 
adhere to them. The feed, after having palled between 
the rollers, falls upon an inclined board, placed in the 
frame beneath them ; and is thus (hot down in a heap be¬ 
fore the rollers, from whence it is conveyed by a labourer 
to the rolling-ltones. 
The prefs comes next to be noticed; for we have hi¬ 
therto only defcribed the machinery for bruifing the feed, 
previous to exprefiing the oil from it. The tumbling- 
(haft, F, has two lifters, M, N, projecting from it, which 
as it turns round lifts up and lets fall the dampers, V, W, 
of the prefs. They rife and fall in a frame confiding of 
two thick pieces of wood, P, P, firmly bolted together at 
the bottom by beams, T, T, extended between them. 
The fpace between thefe beams is filled up by the bags of 
feed at d, d, fig 2. the preffing-wedge b, the difcharging- 
wedge c, and blocks of wood, to keep them at the proper 
diftance apart. The beams, T, T, have crofs-pieces upon 
them, between which the Hampers, V, W, Aide up and 
down : they are lifted up by the wipers or lifters, M, N, 
fixed upon the (haft, F: thefe take hold of tappets or 
chocks projefting from the Hampers, and, railing them to 
the proper height, let them fall on the wedges. When 
they are to be Hopped, the workman pulls a rope, which 
raifes a lever, and holds up the Hamper too high to meet 
the lifter in its revolution. The inverted wedge, c, is 
fufpended by a rope from a wooden fpring, which raifes 
it up, as in the figure, when the other wedge is taken out 
for the purpofe of putting a frefli charge of feed in the 
bags at d d. The opening of the prefs, or the fpace con¬ 
tained between the uprights, P, P, of the frame, and the 
two beams, T, T, has a very flrong caft-iron frame within 
it, which refifts the preffure to rend the prefs open. The 
upper edge of this frame is (hown by the dark line in fig. 
2. and the internal parts are (hown by dotted lines. The 
bags of feed, dd, are included between two iron plates, 
united together at the bottom in the manner of book-lids, 
and the bag is (hut up between them : immediately be¬ 
neath thefe are fmall holes in the bottom of the prefs, at 
which the oil oozes out into fmall pots, h k: the blocks 
which fill up the prefs reft upon the bottom of the 
prefs, to prevent them being carried down by the aftion 
of the wedges which Hide againft them, having thin 
pieces of wood between, to make them Hide eafily by each 
other: the preffing-wedge, b, has its point downwards, 
and is driven by the damper, V: the difcharging-wedge, c, 
is inverted, its fmalleft end being upwards; and this, 
when (truck by the (tamper, W, is forced down, and thus 
releafes the prefs, when it would be exceedingly difficult 
to difengage it by any other means, the preffing-wedge 
being driven in very fait by the repeated blows of the 
(tamper, V. 
Vol. XVII. No, 1188. 
L. 437 
There is likewife a fmall apparatus in an oil-mill called 
th efre-gear, or chaufer-pan, which we have omitted in 
our plate. It is intended to keep the bruifed feed (tirring 
whillt it is heated in a copper pan, previous to preffing, 
as this is found to increafe the produce of oil. The chau«- 
ter-pan confifts of a fmall fire-place, fituated in the corner 
of the mill-houfe, and heated by burning charcoal in it. 
The feed is contained in a circular copper pan, which is 
fet over the fire; and the feed is prevented from burning 
to the bottom of the pan, by a crofs-piece of iron fixed 
to the lower end of a vertical fpindle, which, as it turns 
round in the pan, Hits the feed. The fides of this crofs 
are fet inclined, fo as to fcrape the feed from the bottom 
of the pan, and throw it over the back of the ftirrer. 
The fpir.dle for the ftirrer is put in motion by means of 
a train of fmall wheel-work, receiving motion from a rig¬ 
ger or pulley fixed upon the tumbling (haft, F, by means 
of an endlefs chain or rope. In many of the molt im¬ 
proved mills the chaufer-pan is heated by (team inftead 
of charcoal; in this cafe it has a falfe bottom, on which 
the feed lies, and the Hearn from a boiler is admitted into 
the fpace beneath the bottom. This is found to give the 
proper heat with greater precifion than can be done (ex¬ 
cept by experienced workmen) with the charcoal fire; 
for, if the heat is too great, it makes the oil rancid, and if 
it is too low, the produce of oil will be diminiffied. In 
either cafe the pan mull have a fmall opening on one fide, 
and afluice to (hut it up and keep in the feed until it is 
properly heated. Immediately beneath the door are two 
hoppers, which lead the feed down at the fide of the fur¬ 
nace, and conduft it into the flannel bags, which are 
hung at the lower extremity, or fmall openings of the 
hopper. When the feed is fufliciently heated, and the 
prefs is ready for it, the Huice is opened, and the ftirrer 
throws the feed out into the hoppers and the bags. Thefe 
are made of flannel-cloth, which is found the bed Cub- 
ftance to refill the preffure and admit the oil through. The 
bags, before they are put into the prefs, are flattened 
by the hand, and wrapped up in a long flip of very thick 
leather, which enclofes it, and prevents the bag being 
burft by the preffure. 
In fome mills they take a quantity of their bed feed 
from the (tones, and, putting it into bags, give it a mode¬ 
rate preffure by a fcrew-prefs. The oil thus obtained is 
called cold-drawn, and is fold at a higher price, for the ufe 
of cabinet-makers, who rub their ornamental wood-work 
with it, to give it a polifh. In other work, the cold-drawn 
oil is nothing more than the firft obtained by the prefs, 
but without heating the feed. 
In fome of the Dutch mills, a much greater quantity of 
oil is obtained in the grinding, without,^refl'ure, by hav¬ 
ing the bed of mafonry, which fupports the lower mill- 
(tone, formed into a little furnace, and gently heated. 
But the utmoll care is neceffary to prevent the heat from 
becoming confiderable. This, enabling the oil to diffolve 
more of the fermentable fubltance of the feed, expofes 
the oil to the rifk of growing foon very rancid; and in 
general it is thought a hazardous praftice, and the oil does 
not bring fo high a price. 
Methods of purifying Oil. 
Animal oils are thofe chiefly which require purifica¬ 
tion ; but fome of the vegetable oils require it alfo. We 
(hall therefore begin with M. Thenard’s direftions for 
purifying rape-oil. 
To 100 parts of rape-oil add two parts of concentrated 
fulphuric acid; mix and agitate them together. Upon 
this the oil prefently changes its colour, becomes thick, 
and affumes a blackiff-green appearance; after three 
quarters of an hour it is full of flakes ; at which time 
ceafe to agitate, but add near double its weight of water, 
to carry oft’ the fulphuric acid, which, if fuffered to remain 
too long, would aft too ftrongly upon the oil, and carbo¬ 
nate it. It is neceffary to beat this mixture during at 
lead half an hour, in order to bring the particles of oil, 
5T of 
