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Elliot Snell Hall.

I. A study of some new semipermeable mebranes. II. Experiments on the preparation of porous cups suitable for the measurement of osmotic pressure online

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I, A STUDY OF SOME NETiV SE^.aPERJAEABLE MPJ'IBRANES.
II. EXPERIMENTS ON THE PREPARATION OF POROUS CUPS
SUITABLE FOR THE MEASUREMEl^T OF OSMOTIC PRES-
SURE.



DISSERTATION



submitted to the Board of University Studies
of the Johns Hopkins University in confor-mity
with the requirements for the degree of
Doctor of Philosophy.



by



Elliot Snell Hall



Baltimore, Md,
1904.



Contf?nts.

Page.

Acknowledgment - - - - - - - - - - i

Introduction - - - - - - - - - - 1

I. A Study of some new semipermeable Membranes - - 5

Cells - - - - - - - - - - 5

Solutions used in formation of Membranes - - 6

Electrodes- - - - - - - - - - 7

Removal of Air from Cell-wall - - - - 7

Deposition of Membrane- - - - - - - 8

Methods of measuring Activity of Membranes- - 10

Membranes investigated- - - - - - - 11

Uranyl phosphate - - - - - - - 12

Potassium diuranate - - - - - - 16

Stannous hydroxide - - - - - - IS

Silver cobalticyanide - - - - - - 21

Manganese " _-___ - - - 22

Zinc " 2^^

Cadmium " _ - _-__ - - 26

Mercurous f errocyanide- - - - - - 27

Silver " ___ - -__ - - 28

Stannous " _-_-_-_ - - 29



Uranyl ferrocyanide - - - - - - 33

Conclusions - - - - - - - _ - -__ 44

II. Experiments on the Preparation of porous Cups suit-
able for the Measurement of osmotic pressure- - 47
Description of Mould used in forming Cups - 49
Process of moulding - -_-_ - _ - 49
Dimensions of Cup- - - - - - - 50

Electric Furnace, Description of - - - - - 51

" " , Calibration of - - - - - 55

Gas Furnace, Calibration of - - - - 60

Observations on the burning of Cells - - - 61

Biography - - - - - - - - - - - 80



Acknowledgment.

To Professor Morse, for his kindly instruction
both in laboratory and lecture-room, the author
desires to express his sincere gratitude.

Pie would also acknowledge his great indebtedness
to President Remsen, Professor Renouf , Professor
Jones, Professor Shattuck and Doctor Frazer,



Introduction.

-00-

The study of osmotic pressure which was begun in
this laboratory by Morse and Horn in 1901, has been contin-
ued by Morse and Frazer and others in the face of difficul-
ties much more numerous and more serious than were anticipa-
ted at the outset.

With the discovery of a new and simple method for
the preparation of an efficient semipermeable membrane came
the necessity for a suitable support for the septum and a
device for the accurate measurement of the high pressures

developed within the cell.

(1)
In 1901, Morse and Horn showed that a strong mem-
brane could be deposited upon or within the walls of a poa?-

ous clay cup much more easily and with greater certainty
by electrolysis than by the diffusion method of Pfeffer.
They measured pressures of not more than 4.5 atmosjJheres ,
but there was no indication that the limiting strength of
the manbrane had been reached at this point. It was appa-
rent, however, that the measurement of still greater pres-
sures was dependent upon some more effectual means of at-



(1) Amer. Chem. Jour., 26, 1.



taching the manometers to the cups.

In view of the very hin;h pressures which were subse-
quently obtained, a satisfactory solution of this problem

proved to be very difficult, but it was accomplished in the

(1)

following year by Morse and Frazer, '^ho , after repeated

failures, devised an apparatus which has withstood a pres-
sure of more than thirty-one atmospheres and which pror-ises
to be equal to any strain which the cells themselves will
bear.

The same authors also undertook a more careful in-
vestigation of the cups in the walls of which the membranes
were deposited and made numerous observations on the meas-
urement of osmotic pressures of half nojrmal and normal so-
lutions of cane sugar. They expressly state, however, that
these observations "have thus far been made with reference
to the testing of the construction of our cells and the ef-
ficiency of the membranes prepared by the electrolytic pro-
cess and not with a view to the accurate detennination of
the pressures of such solutions."

Before these accurate determinations could be made
it was necessary to perfect the porous cup which served as
a support for the membrane.

In the meantirie, another important phase of the sub-
ID Amer.Chem. Jour, . 28, 1.



ject was investigated. Morse and Horn and Morse and Frazer
had used only the copper ferrocyanide nembrane. There was
no reason to suppose that a large nxAmber of different mem-
branes might not be found, the varying chemical properties
of which misiht make possible the study of osmotic pressures
of a much greater variety of substances than would other-
wise be practicable.

Part I. of this dissertation deals with an investi-
gation of these membranes.

It has already been mentioned that one of the most
difficult problems to be solved was a method for securing
the manometer in the cell. Another problem, one which has
been beset with obstacles on every hand, is the preparation
of a porous cup which can be relied upon to satisfy the
following requirements:

1. The cup must be very strong. Morse and Frazer,
working with a normal solution of sugar, measured pressures
of about 471 pounds to the square inch, and there is reason
to believe that even greater pressures would have been de-
veloped had not the apparatus been shattered at this point.

2, The cup must be made of very finely divided materials.
Microscopic examination of cross-sections of cells has
shown that those having the finest pores are those which



have given the most satisfactory results,

3. The walls of the cup must be free from "air blisters"
and cavities. It is obvious that at the point where a mem-
brane bridges one of these cavities, it finds no support
and even if it offers considerable resistance to the elec-
tric current used in the proness of its formation, it can-
not be expected to 'vithstand such enoxTious pressures as
those already mentioned.

Aft'sr Linavailing efforts to obtain from potteries in
Boston and Baltimore cups which vould satisfy these re-
(-juirements , the work of making them in this laboratory was
undertaken, and has been carried on since the spring of
1903.

Part II. of this dissertation gives an account of
niynerous attempts made since October 1, 1903, to prepare
cups which would be free from the defects of those previous
ly used.



I. A STUDY OF SOME NEW SEMIPERMEABLE MEKIBRANES.



Cells .

(1)
In the investigation of the new maiibranes, two kinds

of porous cups were used: first, bottle-shaped cups of
from 175 to 200 cc. capacity, and secondly, small, hard-
burned cups such as had been employed by Morse and Prazer.
These had an efi'ective capacity of about 20 gc.

The walls of the bottle-shaped cells afforded such a
poor support for the membranes deposited upon them that even
if the cells themselves had not been deficient in strength,
no very high pressures could have been developed within
these cups, without rupture of the membrane.

They did, however, afford a large surface for the
deposition of the membrane, and hence made it possible to
test the activity of the latter by measuring the rate at
which a sugar solution was delivered from the cup when the
latter was immersed in pure v/ater.

These larger vessels were not at all uniform in qual-
ity and when broken, revealed in almost every case the pres-
ence of pores and air blisters, sometimes as large as the
head of a pin. There is also good reason for believing

(1) B. P. Carver, Dissertation, Johns Hopkins Univ., 1903.
J. P. Coony, " „ .. «



that the effective area varied from ceH to cell, that is,
that certain portions of the wall were not porous, and
hence diminished the rate of endosmose of the solvent to a
corresponding defjree.

On account of this lack of unifojrmity in the texture
and porosity of the cell wall, it was never safe to condemn
a membrane as worthless until it had been tried repeatedly
m different cells and even then its failure t( show activ-
ity or its inferiority to other membranes of different com-
position, might be attributed to imperfections in the cell
quite as justly as to the faulty nature of the septum.
While, therefore, no final conclusions as to the relative
excellence of the membranes can be drawn from the experi-
ments which are described in the following pages, this in-
vestigation may afford a basis for future quantitative work
which will be made possible by the acquisition of satisfac-
tory cells.

Solutions used in the formation of membranes .

Unless otherwise stated, the solutions used in the
preparation of the various membranes were one-tenth noxTnal ,
when first made up. Of course, v^here the electrodes were
of platinum, the strength of the solutions in which they



were immei-'sed became constantly less. The solution around
the cathode was frequently renewed in order to prevent the
accumulation of ^ilkali.

The potassium ferrocyanide employed was recrystalliz-
ed several times from the commercial product. The cobalti-
cyanide was prepared from cobalt nitrate and potassium cy-
anide and was also purified by recrystallization. The oth-
er salts used in the preparation of the various solutions
were taken from the regular laboratory supply.

Electrodes .

Wherever practicable, the anode was of the same met-
al as that of the salt in which it was immersed, but in
most cases both anode and cathode were of platinum. The
outer electrode, which was large enough to surround the cup
without touching it, was usually made the anode; the other
was about 5 cm. in length and was placed within the f-ell.

Remova l of Air from the Cell Wall .

The air v/as removed from the cell wall by the method
of Morse and Horn, which is briefly as follows:

The cell was filled with a dilute solution of potas-
sium sulphate and, surrounded by the platinum anode, was



placed in a beaker cntaining a sufficient quantity of the
same solution to cover the cell. The cathode v/as inserted
and a 110 volt current passed until from 200 to 500 cc. of
the solution had been forced by endosmose through the po-
rous v^alls, in the direction of the current. The form of
apparatus which was used is


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Online LibraryElliot Snell HallI. A study of some new semipermeable mebranes. II. Experiments on the preparation of porous cups suitable for the measurement of osmotic pressure → online text (page 1 of 4)