October 28, 1871.] THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
850 
The mechanical advantage of the compound machine is the 
product of those of its parts, or 
^ C c C 
c p p 
— the ratio of the circumference of the circle described by 
the arm to the pitch of the screw, as stated by Mr. Umney. 
I may illustrate this by giving the dimensions of my own 
press,—a half gallon one, by Maw, Son and Thompson,—as 
also for the sake of comparing them with those of presses by 
other makers:— 
Pitch of screw ..... in. 
Total length of levers . . 14-| in. 
In estimating the power of the press, the arm should be 
•measured from the centre of the screw to the point where the 
force is applied; which, it is clear, cannot be the extremity 
of the lever, but must be the point through which the resul¬ 
tant of the forces exerted by the fingers passes. 
Practically I believe this coincides with the point of greatest 
thickness in the arm, and I find that, in the case given, this 
is distant from the centre of the screw inehes, therefore, 
the pressure obtained by applying a force of 50 lb. to the 
arm 
50.5-5.2.3T416 
To 
9215 lb. or rather more than 4 tons. 
This is abundantly sufficient, unless carefully managed, to 
hurst the cylinder ; and so far as my experience goes, presses 
are most frequently disabled from this cause, and not, as Mr. 
Staples suggests, from the bending or breaking of the screw. 
The suggestion made by the same gentleman that strong 
block-tin would answer for the cylinder of a press made on 
his principle, seemed to me inconsistent with the pressure 
which he calculates is to be obtained, viz. 30 tons; and, on 
examining his account of the model, I find that he claims an 
additional advantage obtained by reducing the bulk of the 
screw; this is a mistake, as an inspection of the expression 
given above will show ; 
if AB 
C c 
cp 
it is evident that no increase or diminution of c, the circum¬ 
ference of the screw, will affect the value of AB. 
Whether he is right or wrong in assuming that the power 
is doubled by the employment of two screws, I will not pre¬ 
fend to decide; but it is self-evident that one assistant cannot 
work both screws at once, and, also, that unless the force is 
applied alternately to each screw in rapid succession, it will 
act obliquely instead of perpendicularly. 
In conclusion, I hope that, among your correspondents some 
will be found undeterred by Mr. Staples’s epithet of “ un¬ 
profitable,” from entering upon a “ discussion of the theore¬ 
tical power of the screw-press,” with a view of clearing up 
this and other doubtful points. 
J. Fred. Brown. 
Sir,—Would Mr. Staples kindly inform me whether he has 
at any time driven his press to the enormous force of, say, 
twenty tons, not to speak of his latest computation ? To my 
way of thinking, after taking into consideration the shape of 
his cross-beam, it seems but strange that his working model 
should have existed for so many years without meeting with 
anything more fatal than one case of undue violence. I would 
venture to suggest, therefore, to those who purpose getting 
presses made after his design, to have them made with more 
depth in the centre of the cross-beam, and also sufficient 
room in the same for the play of the male screws. 
Warrington, October Z&th, 1871. C. E. D. 
Sir,—When I wrote the description of my press, it was to 
give freely to the world the benefit of an implement on which 
I had bestowed much thought, care and labour before I even 
produced the rude model from which my sketch was taken, 
and which I have found from experience to be very simple, 
convenient, of very great power, and last, though not least, 
so inexpensive as to be within the reach of every chemist; for 
I believe, with a fair division of labour, it could be produced 
at a cost much below that of the cumbersome and inefficient 
implement in general use. And there, I had thought, my 
duty ceased ; J neither expected nor desired to be drawn into 
this controversy; but I am prepared to maintain my opinion 
while I think I am in the right. Now, the issue between 
Mr. Umney and myself is limited to the power applied to the 
lever, and I am in hopes of convincing him that my estimate 
is nearly correct. As Mr. Umney again quotes Professor 
Rankine, I must again remind him that such an excellent 
authority would not have given the same estimate of power, 
for intermittent labour, with ample time to recruit the 
strength, as he gives where it is continuous and exhaustive. 
I have just now taken the opinion of a gentleman who has 
looked at and handled my press, and thinks my estimate of 
100 lb. within the mark, as he could apply 200 lb. (not con¬ 
tinuously, but at intervals); being a mathematical scholar, 
well up in the sciences, I think his opinion of some value. 
But as I said last week, do not talk about a thing if it can be 
done; an ounce of practice is worth a pound of theory. I 
challenge Mr. Umney to the following test, in which, per¬ 
haps some other of your readers will aid us. Let the press, 
when in actual use and a fair amount of power applied, be 
turned on its side with the lever projecting horizontally, load 
the end and note the weight required to move it; if Mr. 
Umney’s theory of 50 lb. applied by the two hands to both 
arms of the lever is correct, one arm should move with little 
more than than 25 lb.; I say, “ try if you can do it.” 
October 24 th, 1871. C. A. Staples. 
The Preliminary Examination. 
Sir,—There was a mournful sentence in the last Pharma¬ 
ceutical Journal. ‘‘First, or Preliminary Examination. 
Two hundred and twenty-two candidates presented themselves 
for this Examination on the 2nd of October, eighty-two 
failed.” 
Something is wrong. Either apprentices and young stu¬ 
dents do not care a straw for the subjects on which they are 
engaged save just so far as their study may enable them to 
pass an examination, or else they are miserably trained. 
As every little helps may I be allowed to say a word. 
Before I was an acting Examiner I amused myself by pre¬ 
paring private friends for the Preliminary. It was then viva 
voce. I did this—First I went to the nearest Day School, 
connected either with Church or Chapel, and engaged a 
junior master to attend two nights a week for one hour each 
time, to teach Arithmetic. Secondly, I asked a curate to in¬ 
struct in English Literature and Composition. The advan¬ 
tage of having an educated gentleman to explain the English 
language cannot be over-estimated. The time was divided 
thus—half an hour was devoted to a rigid grind of Grammar 
and Composition: while during the second half hour the 
pupil had to read aloud some book of standard excellence— 
such as the Vicar of Wakefield, The Essays of Elia, Southey’s 
Book of the Church, Ivanhoe, or the Talisman—these works 
being as far removed from Pharmaceutical subjects as the 
East is from the West—also large portions of the Bible, spe¬ 
cially the Psalms and Isaiah—and celebrated known passages 
such as Addison’s Papers in the Spectator. 
Thirdly—I gave two moiming lessons of one hour each in 
Latin. The time was accurately divided (the watch being on 
the table) into two distinct studies—Half an hour was con¬ 
secrated to a thorough grind in Latin Grammar and compo¬ 
sition : half an hour was allotted to the reading of the first 
book of Cassar. 
Three months’ preparation was exacted. At the end of 
the eleventh week, an examination paper was drawn up con¬ 
taining eight questions on each subject—Latin, Arithmetic, 
and English. 
Then, I forbade my student, for the next week to touch a 
book. I put it to his honour, for mg sake, not to tinker up 
his Latin, addle himself over Arithmetic, or exhaust himself 
with English. I certify that I never had one failure, nor was 
it necessary to look to near the gulf stream to find out where 
the name of the candidate was inserted on the list. On a 
calm revision of the matter I do not see where a possibility of 
failure could occur. 
I have written nothing original, nor indeed do my remarks 
seem to myself worth print—my only excuse is the dismal 
paragraph above quoted. I am my brother’s keeper, and it 
is my duty to see after the eighty and two lost sheep straying 
in the wilderness. To them I say—let the dead bury their 
dead—let the past go : Enter once more with full hope the 
intellectual life and recollect the splendid motto “ Hide 
through.” Joseph Ince. 
