Lapas attēli
PDF
ePub

John D. Sherman, Jr., Mount Vernon, New York

Announces the publication of a

Catalogue of the Coleoptera of America, North of Mexico

By

Charles W. Leng

CONTENTS

Pages Introductory Essay on Classification. .

5-38 List of the 18,547 species, with varieties, synonyms, etc., page refer

ences to place of original description, and indication of
distribution

39_342 Appendix—List of Strepsiptera.

343-345 List of North American Coleoptera described as Fossils (By Prof. H. F. WICKHAM)....

347-365 Bibliography of North American Taxonomic Coleopterology, from 1758 to January 1st, 1919 (over 4,000 titles).

367-444 Index of genera, tribes, families, etc...

445-470 Mr. Sherman has no hesitation in offering this great work of Mr. Leng as preeminently the most important book on North American Beetles that has been published since the famous “ Classification" by Doctors Leconte and Horn, issued in 1883.

Mr. Leng's "Essay on Classification," giving a masterly digest of the various systems proposed by different authors, is a feature of the utmost interest, while the Bibliography is something entirely new—and most welcome -in the literature of North American Coleoptera.

PRICE, IN PAPER COVERS, POSTPAIDTEN DOLLARS.

Copies bound in buckram can be furnished to order, in about one month, for one dollar and fifty cents extra.

JOHN D. SHERMAN, JR. 132 Primrose Avenue

Mount Vernon, New York

BECKMANN THERMOMETERS

WITH AND WITHOUT BUREAU OF STANDARDS CERTIFICATE

THE TEST
IN OUR STOCK FOR IMMEDIATE SHIPMENT

OF SERVICE

Beckmann Thermometers, New Model with Auxiliary Scale and
Mercury Trap, with a range of 5° or 6° C divided in 1/100°, reading

A
either upward or downward; with auxiliary scale adjacent to the
reserve reservoir reading from 10 to +140° C in 2° divisions.

C
An improved construction in which the specially designed mercury
trap “A” below the reservoir greatly facilitates setting as com-
pared with former types. Expansion bulb “B” below the mercury
trap provides for expansion of about 35° C before the trap operates.
This feature is of particular value when using the thermometer for
the determination of the depression of freezing points, as it ob-
viates frequent re-setting when working under ordinary conditions.
48289. Thermometer, Beckmann, new model with auxiliary

B в
scale and mercury trap, as above described, with scale
reading upward from o to 5° or 6° C in 1/100° divi-
sions. Without certificate

18.00 48290. ditto, with Bureau of Standards certificate .....

30.50 48293. Thermometer, Beckmann, new model with auxiliary

Detail of Mercury scale and mercury trap, as above described, with Trap and Expansion scale reading downward from o to 5° or 6° C in

Bulb in 48289 1/100° divisions. Without certificate

Je, Thermometer 48294. ditto, with Bureau of Standards certificate ... 30.50

Beckmann Thermometers, original model, identical in construction with our new
model described above, except that'they are furnished without the mercury trap
"A" in the capillary and without the auxiliary scale under the reservoir. Provided
with a mercury expansion bulb in the capillary.
48297. Thermometer, Beckmann, as above described, without auxiliary scale

and without mercury trap; reading upward from o to 5° or 6° C. in
1/100° divisions. Without certificate

15.00 48297a. ditto, with Bureau of Standards certificate

27.50 48298. Thermometer, Beckmann, as above described, without auxiliary scale

and without mercury trap; reading downward from oo to 5° or 6° C.
in 1/100° divisions. Without certificate

15.00 28398a. ditto, with Bureau of Standards certificate

... 27.50 NOTE—The extra price charged for Bureau of Standards certificate includes the

Bureau fee of $10.00, the cost of transportation to and from the Bureau, breakage loss in both transportation and testing, the loss for rejected thermometers, and a reasonable profit on these expenses, which become a part of our merchandise cost when the thermometer is placed in our stock.

18.00 Beckmann

No. 48289

Prices subject to change without notice.

ARTHUR H. THOMAS COMPANY

WHOLESALE, RETAIL AND EXPORT MERCHANTS LABORATORY APPARATUS AND REAGENTS WEST WASHINGTON SQUARE

PHILADELPHIA, U, S. A.

SCIENCE

FRIDAY, JANUARY 28, 1921

ELECTRIFICATION OF WATER AND

OSMOTIC FLOW1

[blocks in formation]

I The exchange of water and solutes between the cell and the surrounding fluid is one of the important factors in the mechanism of life, and a complete theory of the osmotic flow is therefore a postulate of biology. It was a marked advance when the experiments of Pfeffer and de Vries led van't Hoff to the formulation of the modern theory of osmotic pressure. According to this theory the molecules of the solute behave like the molecules of a gas in the same volume and at the same temperature, and the gas pressure of the solute measures the “attraction” of a watery solution for pure water through a strictly semipermeable membrane. Yet it is obvious to-day that in a liquid the electrical forces between solvent and solute must play a rôle and no adequate provision is made for these forces in van't Hoff's law. Traube rejected van't Hoff's theory altogether, suggesting instead that the osmotic flow was from the liquid with lower to the liquid with higher surface tension (and higher intrinsic pressure).

Tinker has shown that van't Hoff's theory for osmosis holds strictly only in the case of ideal solutions, i.e., when the process of solution occurs without heat of dilution and change in volume, but that in the case of non-ideal solutions Traube's ideas explain the deviations from the gas law which are bound to occur. When two different ideal solutions containing equal numbers of particles of solute in equal volume are separated by a strictly semipermeable membrane, equal numbers of molecules of water will diffuse simul

90

[blocks in formation]

1 Presidential address prepared for the Chicago meeting of the American Society of Naturalists, December 30, 1920.

occur.

an

II

taneously in opposite directions through the that water diffuses through collodion memmembrane and no change in volume will branes in the form of positively charged par

When, however, the same experiment ticles. Collodion bags, cast in the shape of is made with two non-ideal solutions contain- Erlenmeyer flasks, are filled with a weak and ing equal numbers of molecules in equal neutral solution of electrolyte, e.g., volume, the result is different. As Tinker M/256 Na, SO4, and dipped into a beaker has demonstrated mathematically, in this case filled with the same solution of M/256 the flow of water must be from the solution Na SO, The opening of the collodion bag having the lower intrinsic pressure and lower is closed with a rubber stopper perforated by surface tension to the solution with higher a glass tube serving as a manometer. When intrinsic pressure and higher surface tension. a platinum wire, forming the negative elecThis is what Traube claims, and his theory trode of a constant current, is put through explains therefore, as Tinker points out, the the glass tube into the collodion bag while deviations from the gas law in the case of the other pole of the battery dips into the non-ideal solutions, but it does not prove that outside solution, the liquid in the glass tube the gas law of osmotic flow does not hold in rises rapidly with the potential gradient bethe case of ideal solutions and Traube's theory tween the two electrodes. The water therecan not therefore replace van't Hoff's theory. fore migrates through the collodion membrane

in the form of positively charged particles.

The writer has made a number of experiThere is a second group of forces not taken ments concerning the osmotic flow through into consideration in van't Hoff's law, namely collodion membranes, and it is the purpose of the influence of the chemical nature of the this address to give a brief survey of the membrane on the solvent. These forces be- results. come noticeable when the membrane separating the solution from the pure solvent is When a collodion bag is filled with a solunot strictly semipermeable. When water is in

tion of a crystalloid, e.g., sugar or salt, and contact with a membrane it undergoes as a dipped into a beaker containing pure water, rule an electrification and this electrification

the pure water will diffuse into the solution of the particles of water plays a great rôle and the level of liquid in the capillary glass in the rate of the osmotic flow when the

tube serving as a manometer will rise. At solution into which the water diffuses is an

the same time particles of the solute will electrolyte.

diffuse out of the bag (except when the solute The assumption that water diffusing

is a protein solution or a solution of some through a membrane is as a rule, electrified,

other colloid). The concentration of a crysis justified by a large number of observations.

talloid solute inside the collodion bag will Quincke demonstrated that when water is

therefore become constantly smaller until pressed through capillary tubes it is found

finally the solution is identical on both sides to be electrically charged (the sign of charge

of the membrane. Nevertheless the relative being more frequently positive); while the

force with which a given solution inside the tube has the opposite sign of charge, e.g.,

collodion bag "attracts” the pure water into negative, when the water is positively charged.

which the bag is dipped can be measured by When two solutions of weak electrolytes are

the initial rise in the level of water in the separated by a membrane (which may be con

manometer, before the concentration of the sidered as a system of irregular capillary

solution has had time to diminish to any tubes) an electric current causes water to

great extent through diffusion. Since in the migrate to one of the two poles, according to the sign of its charge. By this method of 2 Loeb, J., J. Gen. Physiol., 1918–19, I., 717; 80-called electrical endosmose it can be shown 1919-20, II., 87, 173, 273, 387, 563, 659, 673.

III

cane

first minutes accidental irregularities are cation, eg., M/256 LaCly, is dipped into a liable to interfere with the result, we measure beaker with pure water we notice no rise in the rise in the level of liquid in the mano- the level of water in the manometer. In meter during the first 20 minutes.

solutions with bivalent or trivalent cations If the initial rise of level of liquid in the the repulsion of the cation equals or exceeds solution is thus measured it is noticed that it therefore the attraction of the anion for the occurs approximately in proportion with the positively charged particles of water diffusing concentration of the solution when the solute through the pores of the collodion membrane. is a non-electrolyte. The rate of diffusion Hence we conclude from these (and numerous of pure water into a solution of cane sugar similar) experiments that the particles of through a collodion membrane is therefore water diffuse through a collodion membrane approximately a linear function of the con- as if they were positively charged and as if centration of the solute within the limits of they were attracted by the anion of an electroO and 1 M. This is what we should expect lyte and repelled by the cation with a force on the basis of van't Hoff's theory of osmotic increasing with the valency of the ion. pressure.

It seemed of interest to find that concenIf, however, a watery solution of an electro- tration of a cane sugar solution which just lyte is separated from pure water by a collo- suffices to prevent the diffusion of water into a dion membrane, water diffuses into these given solution of an electrolyte. Into each of solutions as if its particles were positively a series of beakers, all containing the same charged, and as if they were attracted by the neutral salt solution, e.g., M/192 Na, SO,, was anion of the electrolyte in solution and dipped a collodion bag containing a repelled by the cation with a force increasing sugar solution of different concentration, from with the valency of the ion (and another M/128 to 1 M, and it was observed in which property of the ion to be discussed later). of these sugar solutions the level in the

Pure water diffuses into a M/128 solution manometer rose during the first 10 minutes, of NaCl through a collodion membrane more in which it fell, and in which it remained rapidly than it diffuses into a M/64 solution constant. It was found that the cane sugar of cane sugar; water diffuses into a M/192 solution which was just able to balance the solution of Na,SO, or Na, oxalate still more rapidly than into a M/128 solution of NaCl; and into a M/256 solution of Na, citrate Approximate Concentration of a Solution of Cane water diffuses more rapidly than into a M/192 Sugar Required to Balance the Osmotic At. solution of Na,SO,, and into a M/320 solu

traction of the Following Solutions of tion of Na Fe(CN), still more rapidly than

Electrolytes for Water into a M/256 solution of Na, citrate. As

Approximate Molecular Concen

Electrolyte tration of Balancing Solution suming complete electrolytic dissociation of

M/128.... KC

M/8 the electrolytes in these cases, the influence

M/192....K.80, Between M/4 and M/2 of the five solutions mentioned should be

M/192....K, oxalate

M/2 identical according to van't Hoff's theory. M/192....K, tartrate... Slightly above M/2 We notice, instead, that the “ attraction” of M/256....K, citrate.... Slightly above 3M/4 the solutions for water increases with the

M/128.... RbCI

M/4 M/128....KCI

M/8 valency of the anion. This is true for all

M/128....Na

M/8 neutral solutions of salts contained in a collo- M/128....Lic

Slightly above M/32 dion bag, regardless of the nature of the

M/192.... MgCl,

M/64 cation.

M/192....Cache

Below

M/64 M/192....srche

Below

M/64 If a collodion bag containing a neutral

M/192. ...Bach,

M/64 solution of a salt with bivalent cation, e.g., M/192.... Cool

Below

M/64 M/192 CaCl, or MgCl,, or with a trivalent M/192.... Mnol

Below

1/64

TABLE I

Molecular
Concen-
tration

Used

of Cane Sugar

« iepriekšējāTurpināt »