November 25,1871.] THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
439 
CffmsptbMt. 
*** No notice can be taken of anonymous communica¬ 
tions. JKhatever is intended for insertion must be authenti¬ 
cated by the name and address of the writer ; not necessarily 
for publication , but as a guarantee of good faith. 
to 
The Improved Tincture Press. 
Sir,—My attention lias been called to several letters which 
have appeared in your valuable Journal relative to the tinc¬ 
ture press. 
Mr. Staples appears to have been the first in the field re¬ 
commending his double screw press in preference to the ordi¬ 
nary single screw, because such screws are subjected to a 
longitudinal tensile strain, instead of a perpendicular thrust 
or crushing strain, this latter having a tendency to bend the 
screw, or force it out of the perpendicular. 
This is quite correct, providing the screw is too small to 
bear the strain, but it is not likely the press maker would fall 
into this error, for presuming that the bending or distorting 
of the screw was a general complaint, some one would have 
surely long since made a press with two screws instead of 
one. 
Mr. Staples’ press is of so primitive a character, that it 
appears to me to be such an one as would probably have been 
made 100 years since, before engineering skill had constructed 
machinery for cutting screws. 
It must not, howevei’, be despised for its primitive cha¬ 
racter, for there is one thing in its favour, it is simple, and 
can be made at a small cost. But as the ordinary screw 
press can be bought of any druggists’ sundriesman for ten 
shillings and upwards, I do not think that the double screw 
press could be made for much less. 
But then Mr. Staples says his press is so much more power¬ 
ful than the ordinary variety, upon which Mr. Umney com¬ 
mented, basing his calculation on the pitch and diameter of 
the screws. This again is quite true, for one can make the 
screws of any power, provided the whole fabric is sufficiently 
strong to resist the pressure; and here it is that Mr. Staples 
is so greatly in error. 
Mr. Staples estimates the power of his press at 20 tons, 
with screws of ^ inch pitch, and ^ inch diameter, or 10 tons 
resistance to each screw; and in his letter of the 21st Oct., 
he thanks Mr. Umney for inducing him to investigate his 
press more closely, and is so astounded at its enormous power 
that he says he feels some diffidence in stating that his esti¬ 
mation is now 30 tons. 
I am really astounded myself, and should like to know 
where the iron was made to withstand such a strain. 
Mr. Staples has quite ignored the all-important point in 
his calculations, viz. the cohesive yoioer of the iron , of which 
the screws are made. 
The argument now wholly turns upon this, and resolves 
itself into the following question:—What is the ultimate re¬ 
sistance of the iron composing the screws ? 
In answering this question, I will give Mr. Staples the 
benefit of the whole diameter, viz. ^ in. 
The ultimate strength of a 1-inch round bar of English 
iron is 4-3,881 lbs., which, divided by 4, is 10,970 lbs. as the 
ultimate strength of a bar of -|-inch diameter; but as the press 
has two screws, 10970 x 2 must be the ultimate strength of 
both screws, or 21,940 lbs. (9‘3 tons) as the breaking-strain. 
Now with engineers it is customary, in order to ensure 
safety, to take the working strain at one-third the cohesive 
power of the iron ; this would reduce the power of the press 
of Mr. Staples’ design to 3 tons 3 cwt. (9'3 -f- 3 - l tons). 
How then is it possible for Mr. Staples to give 30, or even 20 
tons, as the power obtained by his press ? 
Mr. Staples, however, not content with 20 or 30 tons, 
even soars to 50 tons, which astounding and magnificent 
power is (he says) to be obtained and resisted by two 
highly-finished steel screws, with threads of ^ of an inch. 
Now I will give him shear steel, which has about double 
the strength of iron, then 93x2 or 18 - 6 tons would be the 
ultimate strength or breaking-strain. 
Surely, therefore, it is perfectly absurd to talk about 20,30 
or 50 tons P 
Then again, Mr. Staples has said nothing about the dimen¬ 
sions of the wooden base, or his cross bar. 
I see in a very sensible letter in your last issue by Mr. B. 
Groves (who, although not a practical mechanic, has his head 
screwed on in the right direction), that he is the first to make 
allusion to them. 
I should like here to caution Mr. Groves when trying his 
expei iment with his wind-bag, that the highly compressed 
air does not suddenly burst its casement, and send the pieces 
flying at him. It would be far better if he wishes to try his 
experiment, to get a solid lump of india-rubber interposed 
between the marc and the screw; he may rely upon it, how¬ 
ever, that the spring, if tried, will be of no manner of use, 
nothing can be gained by it, for it only forms part and parcel 
of the cross bar. 
Mr. Groves observes that the intensity of the pressure ex¬ 
erted is always proportionate to the area over which it is 
spread, so that the pressure per square inch on the material 
can be made more or less by decreasing or increasing the sur¬ 
face of action. This very sensible remark, which he says 
is often lost sight of, has surely escaped Mr. Staples, for he 
does not even mention the diameter of his cylinder. 
I would certainly advise Mr. Staples to give up the contest, 
for what good has it done ? save that it has brought about a 
contention of who is right in estimating the power of a screw 
press, and whether the power applied should be taken at 50 
or 100 lbs. 
Now the fact is, one can estimate the power at anything 
within the limits of the strength of the materials of which 
the press is composed. 
Anything beyond this is but a reductio ad absurdum. 
“An Old Engineer.” 
Sir,—Mr. Groves essayed to determine, experimentally, the 
power which a man of average strength can exert in turning 
the lever of an ordinary screw-press, by applying, as the re¬ 
sistance to be overcome, a force acting vertically at the ex¬ 
tremity of the lever,—the influence of the iron pulley em¬ 
ployed being merely to change the direction of the force, and, 
by friction, to diminish it slightly. 
If the rope had been attached to the head of the screw, Mr. 
Groves would have succeeded in solving the problem of the 
actual pressure exerted by the tincture press, since the resist¬ 
ance of the marc is a force acting vertically upwards; but 
that as a measure of the manual strength exerted in pressing, 
his result involves a huge fallacy. 
Of course, a resistance applied to one extremity of the lever, 
could only be counterbalanced by a force equal to it, applied 
to the other, since the fulcrum is central; but when a weight 
is raised from the ground by the downward united progress 
of the lever and screw, the mechanical advantage of the latter 
contributes to the result. 
Thus, assuming that the circumference of the screw in Mr. 
Groves’ press was six inches, and the distance between the 
threads half an inch, and disregarding friction, the actual 
manual strength required to lift from the ground a weight of 
216 lb., would be 216 12 = 18 lb. 
This may appear ridiculously below the truth, but it should 
be borne in mind that the press was situated in a recess, and 
the operators may have been thereby cramped for room, also 
that the friction may have been considerable. 
It has occurred to me that the compressor recently de¬ 
scribed in the Times as being employed to ascertain the ex¬ 
pansive force of the charges of powder used for our heavy 
guns, might be adapted to show the actual pressure which the 
press-cylinder and its contents are called upon to resist. 
Dover , Nov. 21st, 1871. J. Frederick Brown. 
[*** Our correspondent appears to have misunderstood 
the arrangement adopted by Mr. Groves, inasmuch as he 
supposes the resistance overcome in the experiment to have 
been a force acting vertically at the extremity of the lever. 
We assume, however, that in Mr. Groves’ experiment the 
resistance acted horizontally.— Ed. Piiarm. Journ.] 
Difficulties in Dispensing. 
Sir,—The recommendation to which T. B. takes exception 
was challenged at the meeting before which my paper was 
read, although not mentioned in the report of the discussion 
that followed, but I really cannot see that the practice is so 
objectionable as he would make it appear. 
I acknowledge that it is our duty as dispensers' of medicine 
to carry out the intentions of the physician, and tlnat we 
ought as far as possible to avoid “making material alteration 
in a prescription without the sanction or knowledge of the 
physician,” but I contend that it is also our duty to present 
