THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. [September 9,1871. 
314 
.male screw being turned by a lever. The effect of this 
method of applying the power is a tendency to force the 
screw out of the perpendicular. But it would bear a 
much greater power without injury if such power were 
applied to the female screw or nut. To make myself 
..better understood, imagine a wire hanging from a beam, 
load it, and notice the enormous weight it will bear with¬ 
out injury. Now reverse the position, and try to sup¬ 
port the weight at the top, it will require a much stronger 
<wire to act as a pillar, or it will bond and the weight 
come to the ground. Now this may be compared to the 
screw of the press : the power applied being usually ex¬ 
pressed as equivalent to so many pounds weight, this is 
. sometimes enormous, and will be understood by the fol¬ 
lowing simple calculation. In a small screw press, such 
..as is usually found in the pharmaceutical laboratory, the 
lever radiates from the centre, say 12 inches, it would 
travel a circumference of over 72 inches for each revolu¬ 
tion of the screw. Now place the rule to the screw, and 
note the number of threads to the inch; if 6, this would 
give 72 x 6 =432, as the number of inches the lever tra¬ 
vels for each inch of pressure obtained; that is to say, 
the power is multiplied 432 times. Now if we imagine 
n force equal to 100 lbs. applied to the end of the lever 
(and this is but a moderate estimate of a man’s strength), 
it would give 432 x 100 = 43,200 lbs. as the weight, such 
pressure would represent; or, we may compare the screw 
.of the press to a column supporting a weight of nearly 
twenty tons ! How is it to support this prodigious 
weight ? Evidently only by increasing its bulk, and 
..consequently the friction, cumbersomeness and expense 
.of the implement. It maybe objected that these figures 
are somewhat theoretical. I use them as an example of 
jthc laws by which the force of mechanical powers is 
usually computed, but I am sure it will be readily con¬ 
ceded that if well applied, the power of a good screw- 
press is very great, and that if cases do arise where it 
fails to meet the requirements of the pharmaceutical 
laboratory, they must be extremely rare. The next de¬ 
fect to be noticed in the iron frame press is its rigidity ; 
the pressure ceases the instant the hand is taken from 
fhe lever; now to bring the expression of a large mass 
of tincture to a successful and economical termination 
will occupy several hours, during the whole of which 
June it should be subjected to a steady, firm, but elastic 
pressure. At first it must be very gentle, or the sub- 
;stance will be forced through the holes or the cylinder 
burst open, but as the process advances, more pressure 
.should be applied, and gradually increased until the full 
power of the press is brought into use. Now it is evi¬ 
dent that this uniform pressure cannot be obtained by 
an implement, the excellence of which consists in the 
firmness of its parts, without the uninterrupted labour 
of some one with his hand on the lever to keep the pres¬ 
sure constantly applied, requiring an amount of time 
.and labour that would add greatly to the cost of the 
production, and that might be saved by an improvement 
in the machinery. The next defect we observe is, that 
an additional vessel (generally an evaporating basin) has 
.do be used to receive the expressed juice as it flows from 
vthe spout at the bottom of tho cylinder; this may appear 
a trifle, of which it is frivolous to complain, but where 
.the press is portable, it sometimes causes considerable 
annoyance and loss. The assistant endeavours to steady 
the press with his foot, from which it frequently slips, 
. and the basin may be overturned or broken, and the 
.product wasted. Taking all these defects into considera¬ 
tion, and thinking that my slight mechanical knowledge 
anight enable me to design a press in which some of them 
would be remedied, I drew a rough sketch of my idea, 
. and had the parts manufactured in a simple inexpensive 
manner, so as to produce a working model, from which 
J[ purposed constructing a more perfect and highly 
finished implement when I had discovered and corrected 
- tho faults which only experience could detect. I have 
endeavoured to represent it as it appears, but I am not 
a draughtsman, which 1 trust will be my apology for the 
rudeness of the sketch. 
A is a strong platform of oak plank, into which two 
square iron bolts secured by broad flat heads are firmly 
fixed, rising perpendicularly to it, and parallel to each 
other, and having a screw-thread cut in them about half 
their length. B is a spouted basin of tinned plate to 
receive the expressed juice. C is the cylinder of tinned 
iron plate pierced with fine holes. The block D, of 
turned wood covered with tinned plate, is forced into 
the cylinder by the wooden cross-beam E, which has a 
hole at each efrd, through which the screws pass, large 
enough to allow it to slide freely up and down the screws, 
and armed with a piece of polished iron plate to diminish 
friction. The power is applied to the nuts or female 
screws, polished at the bottom and furnished with wooden 
handles FF, these are purposely omittod at the right to 
show tho form of the nuts as forged by the smith. The 
cylinder holds half a gallon. I have also one holding 
about 1 pint. Several of them of various sizes might be 
used by the same press. 
This simple inexpensive implement possesses many 
advantages; it is light and portable, works easily, ha's 
very great power, and as the power is applied in the 
best manner, the strain is very slight, and tho friction 
less than would be expected. I have had it in U3e about 
fifteen years, it has never got out of order, or required 
any repairs (excepting an accident from undue violence). 
Of course it would be better if tho workmanship were 
more highly finished ( e . g. with steel screws substituted 
for iron), but as my old model is still in such good work¬ 
ing order, I have not yet replaced it by the more perfect 
implement, or discovered the faults that I expected I 
should have to correct. The only improvement I can 
suggest is the increase of its elasticity; and this I would 
propose to accomplish by a powerful steel spring screwed 
to the centre of the cross-bar, and rising a little from it 
at each end, somewhat in the form shown in the sketch. 
Sketch of proposed Spring. 
Without experience I am not prepared to give the exact 
size and substance of the spring, but I think it should 
be about 2 inches broad, inch thick in the centre, 
decreasing to about -g- at the ends. The holes through 
