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Repeated object lessons have demonstrated that nearly all progress in science has resulted in important advances in industry

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G-E Research Laboratory

Schenectady, N. Y.

Among the many products developed by the General
Electric Company's research laboratories the following
are of special interest to manufacturers:

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For further information address Supply Department, Schenectady Office.

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General Electric

Company

General Office
Schenectady. N.Y.

Sales Offices in all large cities

35B-48

RAYLEIGH-HILGER GAS INTERFERENCE REFRACTOMETER

THE TEST
IN OUR STOCK FOR IMMEDIATE SHIPMENT

OF SERVICE

DZE

ADAM HILGER LO LONDON.

Interference Refractometer, Rayleigh-Hilger for Gases. This instrument is designed for work on the refractometry of gases, of which the refractive indices differ so little from unity that a very high degree of sensitivity is required in any refractometer to be used with them. Some idea will be obtained as to the sensitivity of the instrument when it is stated that it is possible by means of it to detect the presence of .01% of hydrogen in air, a quantity which causes a change of refractive index of only .000,000,015. The principle underlying the design of the instrument is that of the interference bands formed by two adjacent slits in collimated light, and observed by means of a telescope. The arrangement is, in fact, a diffraction grating with only two openings. The means whereby the system of bands thus obtained is made to indicate the refractive index of a substance is provided by the sideway shift of the whole band system when any change is made in the optical path of one of the interfering beams; part of the optical path being, of course, the substance under examination.

Quantities of Gases in Air Detectable by Rayleigh Interference Refractometer Minimum observable shift assumed to be 1/40 band. Hydrogen.. .01% Helium. .006% Chlorine....

.003% Nitrogen. .3% hur Dioxide .034% Carbon Monoxide.

.03% Nitric Oxide .0065% Water....

.04% Carbon Dioxide.

.0095% Argon.

.15%
Hydrogen Sulphide .0045% Ammonia ....

.017% Bibliography of Rayleigh Interference Refractometer Original Arrangement and Laboratory Type Lord Rayleigh..

{ . : : ): Proc. Roy. Soc. (A) rol. 59, p. 201 (1896).

Proc. Roy. Soc. (A) vol. 62, p. 225 (1897). Ramsay & Trarers.

( Proc. Roy. Soc. (A) vol. 67, p. 331 (1900). Travers

"Study of Gases," Macmillan, 1901.

Technologic Papers of the Bureau of Standards. J. D. Edwards.

No. 113.

Jour. Amer. Chem. Soc. 39, p. 2982, 1917. Adams...

Jour. Amer, Chem. Soc. 39, p. 1181, 1915. 45940. Refractometer Interference, Rayleigh-Hilger, for gases, with double gas tube 100 cm. long, but without illuminating lamp...

..654.75 NOTE-By the substitution of a Liquid Cell in place of the Gas Tube, the Rayleigh Interference Refractometer can be converted into an instrument for the investigation of liquids, or can be furnished for this purpose without the Gas Tube. Prices on application.

Prices subject to change without notice

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ARTHUR H. THOMAS COMPANY

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

PHILADELPHIA, U. S. A.

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ON ACOUSTIC PRESSURE AND

ACOUSTIC DILATATION 1. Introductory. Apparatus.-On a number of occasions, heretoforel I have endeavored to use the interferometer for the measurement of Mayer and Dvorak's phenomenon: but though the experiments seemed to be well designed and were made with care, they invariably resulted in failures. The present method, however, has been successful and led to a variety of results.

The apparatus is shown in Fig. 1, where B is a mercury manometer described elsewhere, the displacements being read off by the component rays LL' of the vertical interferometer. The mercury of the U-tube is shown at min m', above which are the glass plates g, g', the former being hermetically sealed, the latter loose, so that the air has free access. The closed air chamber R above m, receives the air waves from the plate of the telephone T by means of the quill tubes t hermetically sealed into the mouthpiece of the telephone, and ť sealed into the manometer. Finally, t" is a branch tube ending in a small stopcock C or similar device at one end, while the other communicates with tt'. Flexible rubber tube connectors may be used at pleasure, so long as the space bounded by the outer face of the telephone plate, the mercury surface m and the stopcock C is free from leaks.

The cock C will eventually be replaced by the glass tubes c and c' (enlarged) perforated with minute orifices at O at one end and open at the other.

The telephone is energized by two storage cells and a small inductor with a mercury or

1 Carnegie Publ., No. 149, part III., pp. 206-08, Washington, 1914, and subsequently. The phenomenon has been studied by Rayleigh, Kolacek, Lebedew, Wien, Geigel and others. As to hydrodynamic forces in pulsating media, the researches of Bjerknes and W. König should be mentioned.

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ical Society: DR. CHARLES L. PARSONS.. 504

M88. intended for publication and books, etc., intended for review should be sent to the Editor of Science, Garrison-ORHudson, N. Y.

other break. Large resistances are to be put When the cock C is closed there is no in the telephone circuit so that the induct- appreciable effect until the telephone resounds ances are of secondary importance. The bore harshly. In such a case there is marked of the tubes t, ť, c, d need not exceed 5 mm. dilatation in the resonator R, increasing with Thus the chamber in B, about 6 cm. in the intensity of vibration. The successive diameter and 2 cm. deep, is the resonator readings (s' fringes) are liable to be fluctu(capacity 57 cm.) of the apparatus.

ating, but the sign and mean value is definite

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The displacements of the achromatic fringes Since for s' - 8=: the head is s1/2 (the corresponding to the head of mercury in B displacement being s fringes of wave-length may be read off by a telescope provided with »), this mean value, s=7 fringes for the an ocular .1 mm. micrometer. It is perhaps given intensity of vibration, is at once equivaadvantageous to place the micrometer in the lent to Ap=2 X 10-4 cm. of mercury, or to wide slit of the collimator, the fringes being about 3 x 10-6 atmosphere. If but 500 ohms parallel to the scale parts. To obviate the are put into the telephone circuit, however, need of adjusting the inclination of the appreciable deflection ceases. fringes (as this frequently changes), the slit Again, if the stopcock C is completely open holder should be revolvable around the axis no effect whatever is obtained. The bore of of the collimator, the scale being parallel to the small stopcock in this case need not exo the length of the slit and the fringes moving ceed 2 or 3 mm. All the negative results in the same direction across the white ribbon- which I obtained by other methods heretofore like field. Fringes equal to a scale part in are thus explained. breadth are most convenient.

3. Resonator All but Closed.-If now the 2. Observations. Closed and Open Resona- plug of the cock C is rotated from the open tors.--Spring interruptors dipping in mercury position gradually until the opening is rewere first used, having frequencies of n=12 duced to the merest crevice, the fringe deand 100 per second, respectively.

flection s will, on further slow rotation, be found to increase from zero, with great as above 10-4 amperes per fringe, may be rapidity to a positive maximum. The de- increased. flection then falls off with similar rapidity 6. Pin Hole Sound Leaks.-Pin holes less through zero to the negative value when the than a mm. in diameter seem more like a procock is again quite closed. I have indicated vision for light waves, than for sound waves this result graphically in Fig. 2, in which the often several feet long; but one may recall abscissas show the degree to which the cock the phenomenon of sensitive flames. has been opened and the ordinates the fringe It is so difficult to make the fine adjustdeflections, s, obtained. The maximum pres- ment for maximum conditions with stopcocks sure obtained in these initial experiments was that their replacement by the devices given in the equivalent of about 50 fringes; i.e., c and c', Fig. 1, is far preferable. Here c is Ap=1.5 X 10-8 cm. or about 2 x 10-5 atmos- a quill tube, to one end of which a small phere for a frequency of about 12 per second. sheet of very thin copper foil has been fastAt higher frequencies this datum is much ened with cement. The sound leak at O is increased.

then punctured with the finest cambric needle. These pressures are real: for on suddenly The other end (somewhat reduced) is thrust closing the cock at the maximum and break

into a connector of rubber tubing at t". In ing the current, they are retained until dis- case of the tube has been drawn out to a charged on opening the cock.

very fine point. This is then broken or 4. Pressure Depending on the Frequency ground off until the critical diameter (.04 cm.) and on the Intensity of Vibration.-The is reached. Both methods worked about maxima are observable for very considerable equally well but in the case c several holes reductions of the intensity of vibration. In side by side or holes of different sizes may be Fig. 3 curves 3, 5, I have given examples of tried out.

tried out. Such results are shown in Fig 4, the observed fringe displacement; s, when which exhibits the deflection (8 fringes, ordidifferent resistances (given by the abscissas in nates) for different diameters of hole in mm. 105 ohms) are put in the telephone circuit. (abscissas), when 1,000 ohms were put in the In curve 3 the frequency is n=12 per second. telephone circuit. It will be seen that the Curve 5 contains similar results when the optimum .4 mm. in diameter is quite sharp. frequency is n=100 per second. The sensi- The finest size of needle is needed. tiveness has obviously greatly increased and An example of results obtained with the in a general way this is the case for higher sound leak c when different resistances are in frequencies.

circuit, is given in Fig. 3, curve 8. The value 5. Fringe Deflection Varies as Current In of rs; viz., tensity.-The graphs, Fig. 3, are roughly

51 25 16 12 10 5 fringes hyperbolic, so that the equation rs=

=C (r be-
10-8
1 2 3 4

10 ohms ing the high resistance inserted into the tele

10-18 51

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50 phone circuit) may be taken to apply within the errors of observation for resistance ex- is much more constant than hitherto and ceeding 1,000 ohms. So computed for con- reaches 50 X 10-8. Hence at 100 ohms the venience rs is 24 X 103 in series 3 and pressure increment should be Ap=1.5 X 10-2 36 X 103 in series 5. Hence at r= 100 ohms cm. of mercury. the pressure would have been 7 X 10-8 and Figure 5 finally indicates that the multi1.1 X 10-2 cm. of mercury. The instrument plication of pinholes, all of the same diameter taken as a dynamometer is thus noteworthy, (.04 cm.) is similarly disadvantageous. The since its deflections would vary as the first deflection for four holes is scarcely half as power of the effective current or i=1,8. It is large as for one. of interest, therefore, to ascertain how far the If with the current on, a drop of water is sensitiveness which can not here be estimated placed on the hole o in c, Fig. 1, the pressure

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