US2483102A

US2483102A - Refractometer employing photosensitive devices and use of the same

Info

Publication number: US2483102A
Application number: US591468A
Authority: US
Inventors: Robert M Pierson
Original assignee: Individual
Current assignee: Individual
Priority date: 1945-05-02
Filing date: 1945-05-02
Publication date: 1949-09-27
Anticipated expiration: 1966-09-27

Description

Sept. 27, 1949.

R. M. PIERSON REFRACTOHETER EMPLOYING PHOTOSENSITIVE DEVICES AND USE OF THE SAME Filed May 2, 1945 INVENTOR ROBERT M. /ERsoN ATTORNEY Patented Sept. 27, 1949 UNITED STATES PATENT OFFICE REFRACTOMETER EBIPLOYLNG PHOTOSEN- SITIV E DEVICES AND USE OF THE SAME Robert M. Pierson, Hudson, Ohio Application May 2, 1945, Serial No. 591,468

(Cl. 3l6-32) 18 Claims. 1

This invention relates to reiractometers enrpioying photosensitive devices and to their use in measuring and controlling the composition of a fluid, etc. More particularly, the invention relates to following a. refracted beam or beams, the follower or followers being used for indicating or recording changes in the fluid, etc. The invention includes both the process'end apparatus therefor.

In the chemical industries where knowledge of the composition of any fluidv being treated is desired, this can, in many instances, be determined through changes in the angle of refraction of a beam of radiant energy passed through it. The fluid must be translucent to the radiant energy, and other conditions must be kept constant, or corrections must be applied. For instance, in the case of a liquid, its temperature as well as its composition will affect the refractive index; and in the case of a gas the refractive index is dependent on both its temperature and pressure as well as its composition.

According to one embodiment of this inven tion, by following cl'ianges in the angle of refraction of a beam of radiant energy of a particular wave length passed through a fluid, its composition may be indicated or recorded. Also, such changes may be utilized to bring about some desired result. For instance, in concern-- trating a solution, when the angle of refraction reaches a predeterminedvelue, further concentration may be prevented, or some ingredient may be added, or the cooling of the solution may be initiated, or the solution may be transferred to another vessel, etc. In the handling 01' a dangerous gas, a change in the refractive index may be followed; and when a. predetermined maximum is reached, an alarm may be given to indicate that an explosive or toxic composition has been formed. Gases under pressure lend themselves to the purposes of this invention better than gases at atmospheric pressure.

According to a further embodiment of my invcntion, changes in the difference in refractive indices of a fluid at two or more segregated wave lengths i. e, changes in the refractive dis-- persion of a fiuid-a-re used to determine or com trol, etc., the composition of the fluid. in ham dling or treating mixtures of components having substantially the same refractive index at a particular wave length, it will often be found advantageous to use changes in the refractive dispersion instead of changes in the refraction of a single beam. As explained below, one important advantage in this lies in the fact that,

in general, the dispersion of a substance is considerably less affected by temperature changes thanis its refractive index.

It is an advantage of this invention that the recording, etc., is effected without bringing a sensitive element into physical contact with the fluid and without the attention of some one being devoted to making analyses, etc. Furthermore, the human element is minimized or totally eliminated. The only limit to the applicability of the invention is the requirement that the fluid being measured be sufficiently translucent to radiant energy of some particular Wave length or wave lengths to which photosensitive apparatus is responsive.

It is an important advantage of the invention that the eflicient operation of the method and apparatus is not vitiuted by changes in those optical properties of the fluid, such as absorption and turbidity, which might be very large relative to the changes in refractive index and con"- position.

r pingence or According to my invention the fluid being measured is contained in or run continuously through a hollow container and refracts one or more beams of collimated. monochromatic radi ant energy, the direction of whose emergent path serves to measure or control the composition of the fluid or effect some other operation by the impingence of the beam or beams on photosensitive apparatus; Although not necessary, it will often be convenient to use a beam or beams whose cross section is exceedingly small, the operation being reflected by the imnonimpingence of substantially the cntire'transverse area oi the refracted. beam on a light-semitivc surface or segregated portions thereof.

The operation does not rely on the relative proportion or the beam intercepted by a lightsensitive surface. It does not depend upon measuring the varying amounts of current generated in the photosensitive device correspond ing to the interception of varying proportions of the beam. of radiant energy but requires only that at times some detectable amount of current be generated by impingence of any portion of. the radiant energy of a beam on the photosensitive area and that at other times no current at all be generated due. to nonimpingency of the beam on any portion thereof. The shape of the beam is immaterial. At times it may be desirable to use a. beam of small cross-sectional area, such as shown in the drawings, but this is not necessary because the narrow edge portion of a.

wider beam may, likewise, be employed. Thus, the location of the edges of the beam first intercepted by the photosensitive surfaces will be of importance (the beam being nondivergent due to the monochromaticity and the collimation of the radiant energy), and shifts in the direttion of the beam whose dimension in the line of travel will bring varying proportions of the beam on the photosensitive surfaces are, therefore, not intended to affect the operation of the device.

The invention will be further described in connection with the accompanying drawings in which:

Fig. 1a is an elevation, largely diagrammatic, of apparatus for generating a coilimated beam of radiant energy and passing it through a fluid with means for recording changes in its angle of refraction;

Fig, 1b is a plan view of the same showing more completely the equipment for adjusting the position of the photocells;

Fig. 2 is a plan view of a portion of the apparatus shown in Fig. 1b, with the photocell carrier equipped with maximum and minimum stops;

Fig. 3 is a plan view of photocells equipped with direct control means, though not equipped for indicating or recording; and

Fig. 4 is a plan view of means adapted to utilize changes in the refractive dispersion of beams of different wave length.

In Figs. la and 1b the fluid l flows through the hollow prism 2 (shown in section in Fig. 1b) which has faces 3 and I transparent to the radiant energy. A mercury lamp 5 is used as the source of monochromatic light whose radiant energy is diffused by the screen 6, collimated by the lens 1. For the purposes of illustration, a narrow beam 8 is shown which passes through the slits 9 and Ill and whose undesirable wave lengths are eliminated by filters l Two photocells l2 and [3 are mounted on the movable carriage H! which slides upon the fixed ways l5. They are disposed adjacent to the closely spaced mirrors I6 and i! so that light intercepted by either mirror will be reflected into its adjoining photocell. The carriage I4 is connected to a pen arm 18, pivoted to swing about the fixed point l9 and which records on the chart 20. The position of the carriage I4 is regulated by the reversible motor 2| which is operated by an external source of current (not shown) through either of the photocells l2 or l3 and suitable amplifying apparatus 22.

In operation, the refracted beam 8 will have an emergent direction dependent only upon the refractive index of the fluid and will impinge upon a null point 24 between the mirrors l6 and H. An increase in the refractive index of the fluid causes the beam to move so as to impinge upon the mirror l6 and thus on the photocell l2. The electrical impulse thus generated and amplified causes the motor 21 to turn in a direction such that the carriage M, to which it is connected by the gear arrangement 25, will move to a point where the beam is again in the null position between the mirrors l6 and IT. This moves the pen arm l8 which records the change on the chart 20. Conversely, a decrease in the refractive index of the fluid will cause the beam to impinge upon the mirror I! and thus the photocell l3, resulting in the motor's turning in the opposite direction.

The width of the null point between the mirrors is approximately that of the slits 8 and I0 and,

therefore, also equal to that of the beam at its point of impingence since the beam is not diverged or dispersed due to its collimation and monochromaticity.

It is evident that the sensitivity of the instrument can be enhanced to any desired degree by mere prolongation of the optical path bet een the prism and the photocell, such increases .a sensitivity being, in general, limited only by the accuracy with which it is possible to measure and compensate for other properties of the fluid affecting its refractive index, such as temperature. By adjustment of the amplifying appsratus so that only a minute amount of incident radiant energy is required to actuate the motor, the system is made independent of the relative energy content of the beam, providing Olly that it is above some lower limit. The operation of the instrument is, therefore, independent of large variations in other optical properties of the fluid, such as absorption and turbidity, which may occur concurrently with negligibly small changes in its refractive index but which would substantially alter the energy content of the emergent beam. Similarly, fluctuations of the intensity of the radiant energy source, such as might be caused by line voltage surges, or gradual change in the emission characteristics of the source with time will have no effect on the accurate operation of the instrument. Also, the operation is unaffected by changes in the photocell emission characteristics.

Instead of passing the beam through a segregated flowing fluid, it may be passed through a stationary or agitated fluid in a reaction vessel or the like.

Although not ordinarily the most desirable method, the source of the energy might be located within the fluid so that it passes directly into the fluid without first passing through the surr0unding atmosphere. Likewise, the beam may be made to impinge upon a reflecting surface within the liquid whose plane is at an angle to the plane of the transparent face through which the beam passes, so that changes in the direction of the reflected beam are utilized. In these alternative arrangements for obtaining the same end as hav ing the fluid flow through a prism, the operation of the instrument by effecting control by impingence or nonimpingence of the entire beam or any substantial portion of it on the light-sensitive surface remains the same.

In Fig. 2 the carriage 26, whose position is adjusted as the direction of the beam changes, is connected with an operating arm 21. When the direction of the beam reaches a predetermined maximum or minimum, a conducting point on the arm 21 makes contact with the point 28 Or 29, thereby closing one circuit or the other and setting in motion thereby a motor or valve or other mechanism to effect some desired result. Such equipment might, for example, be used in a mine where the maximum and minimum refractive indices might be used to set off different signals to denote that the composition of the gas had become explosive or the oxygen content had become dangerously low, etc. The pen arm 30 is for recording as in Figs. la and 1b.

In the arrangement shown in Fig. 3 the energy output of the

separate photocells

35 and 36 produced by changes in the direction of the beam 31 operates auxiliary amplifying apparatus 38 which, in turn, through the connections 39 operates suitable valves, pumps or motors to control the fluid composition as its refractive index. increases or decreases, as by either adding water or other diluent or adding a concentrate, etc. The width of the null point 40 is variable and is preferably wider than the beam by the amount of lateral travel between the mirrors 4! and 42, which the beam will make as it fluctuates within the allowable limits of concentration of the fluid.

In addition to measurement or control, etc., of a composition through changes in the refractive index at one wave length, changes in the dispersion of the fluid may be utilized. For this purpose changes in a second beam of different wave length must also be considered. The second wave length is preferably well segregated in the radiant energy spectrum from the first in order to obtain the advantages of the largest possible changes in dispersion. The fluid is contained in or run continuously through a hollow container and refracts the beam of collimated radiant energy whose spectral composition has been reduced to two monochromatic wave lengths by appropriate filters. The direction of the emergent path of an element of the beam at one wave length serves to partially measure or control, etc., the composition of the fluid, as described in connection with the preceding drawings. Using this beam element and its associated photosensitive devices as a reference, angular separation between it and the beam element of the second wave length, which is associated with other photosensitive devices, serves as a measure of the dispersion and, therefore, of the composition of the fluid through which the beam haspassed.

By the use of a multiplicity of very closely spaced photosensitive surfaces disposed in the range of the beam element of the second wave length, a wide range of control or the initiation of numerous operations is possible. The photocelis disposed adjacent the first beam element are mounted and equipped with means which causes them to follow this beam element. The photocells disposed adjacent the second beam element are either provided with means which causes them to independently follow their beam or to move with the first-mentioned photocells. If the latter, their movement may exactly duplicate that of the first-mentioned photocells or the two sets of cells may move different dis tances, as by causing one set of photocells to move but a fraction or multiple of the distance of the other set.

If photocells are mounted on opposite sides of each beam element and are provided with means which cause them to separately follow the respective beam elements as described in connection with the use of a single beam element, the angular distance between the pairs of photocelis may be measured by mechanical linkages according to means well known in the art. Changes in the angle may be utilized in any desired manner.

Fig. 4 relates to equipment designed to take advantage of the changes in the dispersion of refracted light from two beam elements of segregated wave lengths. The light source, collimator, slits, filters. etc., required to produce a coilimated beam of two monochromatic wavelength elements are not shown as the equipment used may be the same as in Figs. la and lb, except that the filters are so chosen as to allow the passage of a second wave length. The beam 45 on passing through the hollow prism 46 containing the fluid to be tested is refracted into the two elements H and 48, the latter being of the carriage is equipped to follow the beam 41 and keep it centered in the null point between the mirrors. The pen arm 54 may be used to record the position of the carriage. or it may be omitted.

Associated with the beam of shorter wave length 48 are the photocells B5, 56, and 51 also ailixed to the carriage 53 but divorced from the circuits which control its position. Thus,.as the composition of the fluid in the prism 4 6 varies so as not only to cause changes in the reference beam element 41 but also to cause changes in the angle between the beam elements ll and 48. the beam element 48 will traverse the small arc mirror 58 and be reflected separately into the photocells 55, 56, and 5'! or directed back upon itself. As the reflected beam element initiates responses in the several photocelis, a number of operations may be initiated corresponding to changes in the angle between the beams, such operations being made optionally dependent upon or independent oi the position of the reference beam element 41 and hence of the carriage 53.

Where advantageous, the arc mirror-58 and three photocells 55, 56, and 51 may be replaced by two photocells and angled mirrors, such as shown for use in connection with beam element 41, and these may be mounted on a carriage which operates independently of carriage 53, and

this carriage may be made to follow the beam 48 in the manner described. The movement of this other carriage may be used for recording or for carrying out desired operations, for example, such as those suggested above.

It is to he understood that although mirrors are used in Figs. 1-4 for diverting the beams on the photosensitive surfaces of the photocells, the beams may be made to fall directly upon these photosensitive surfaces or on the surfaces of a multiple cathode photocell although ordinarily the use of mirrors, as shown, will constitute a preferred arrangement.

The following examples. illustrate how the selleral types of equipment shown in the drawings may be utilized. It is to be understood that the examples are illustrative only, and the invention is not limited thereto but is of eneral application.

In the first example, assume that it be desired to measure or control the concentration of a sugar solution of approximately per cent concentration to the nearest 1 per cent. At 68" F. the refractive index n of a 50 per cent sugar solution is 1.4200 for sodium 1) light, and

(In a -"0.0021

where c is concentration in per cent by weight of sugar. Referring to Fig. 1 and. assuming the width of the beam 8 to be equal to the distance between the mirrors I5 and I! and that a change in concentration of 1 per cent in the solution is to correspond to a lateral movement of the light beam in the plane of the photocells equal to the 7 width of the beam, and assuming for convenience that this width ofthebeam and the distance between the mirrors are equal to 0.10 inch (the other cross-sectional dimension of the beam being preferably approximately the length of the photocell cathodes), the placement of the elements of the apparatus shown in Fig. 1 may be as follows:

If the ways IS, on which the carriage l4 and the photocells l2 and I3 are mounted, are parallel to the face 3 and the defining dimensions of the apparatus are: prism angle=60, angle of incidence of light into face 3:45, distance of the point at which light enters face 3 from the apex of prism-: inches; then the distance between face 3 and the plane of the photocells which will give a lateral displacement of the beam equal to 0.10 inch when a change of 1 per cent in sugar concentration has taken place, is 28 inches, the beam intersecting the plane of the photocells about 9 inches from that point in the latter plane perpendicularly opposite the point where the light enters face 3.

Changes in the sugar concentration will result in displacements of the beam equal to 0.10 inch for each 1 per cent change in concentration, the temperature being maintained at 68 F. The sensitivity of the instrument can be doubled to measure or control the concentration to the nearest 0.5 per cent, either by doubling the distance between the plane of the photocells and the face 3 or by halving the width of the beam to 0.05 inch, an desired degree of sensitivity being achieved by either or both of these means.

It is thus seen how the apparatus shown in Fig. 1 may be used to measure and record changes in the concentration of a sugar solution and how the exact position of the various elements may be calculated in advance. It is also evident that such calculations are possible without advance knowledge of the exact emission characteristics of the light source and photocells, the transmission of the solution or the electrical constants of the amplifying devices. Calibration of the systern in terms of these elements is unnecessary since it is required only to adjust photocell sensitivity so that the magnitude of changes in light flux of the order to be exposed will activate the amplifiers. By computations similar to those in the preceding paragraph one may calculate where to place the stops 28 and 29 of Fig. 2 or the mirrors 4| and 42 of Fig. 3 so that by passing a beam of sodium D light through the sugar solution in a continuous concentrator (or in a sampling tube connected with a concentrator), one may automatically increase the rate of feeding steam to a concentrator if the concentrating of the sugar solution lags or, conversely, bleed air into the vacuum line of the concentrator if the concentration exceeds a. desired maximum.

Another example of the use of my invention is in the extraction of pyridine cases with dilute sulfuric acid from the heavy oil residue of coaltar distillations. The difference in refractive indices of pyridine and 5 per cent sulfuric acid solution would be such that measurement or control of the solution to within the nearest 1 per cent of pyridine could be obtained by measuring or controlling the refractive index to approximately .0011 to .0012. Since, as has been pointed out in the description of the instrument, it is possible to expand the optical dimensions of the instrument so that any desired degree of sensitivity can be obtained, the principal limitation to the sensitivity which can be achieved will be for practical purposes the closeness of control over temperature. If this can be controlled or compeniated for to the nearest 1 (3., corresponding to a change in refractive index of less than 0.0001 in the case of dilute aqueous solutions, it is evident that the concentration of the acid aqueous phase containing pyridine bases could be controlled or measured to within 0.1 per cent pyridine.

The apparatus of Fig. 1 may be used to record the pyridine content of such an extract at all times. Apparatus such as shown in Figs. 2 and 3 may be used to control the operation as desired. Turbidity in the extract will not interfere with the accurate functioning of the apparatus.

Similarly, phenols and cresols are customarily removed from the portion of coal-tar distillates boiling between 200 and 270 C. by agitating the latter with 10 to 15 per cent caustic solution. forming sodium phenolate and sodium cresylates in the aqueous phase. The difference in the refractive indices of the salts thus formed and the raw caustic solution is of a magnitude such that a change in refractive index of 0.0020 corresponds to a change of 1 per cent in the concentration of the salt. Thus, if the solution temperature be controlled or compensated for to within 1 C., the concentration of the solution can be measured or controlled to within 0.05 per cent of the extracted salt.

The following example illustrates a. use for the apparatus shown in Fig. 4 in which changes in the refractive dispersion of two beam elements are utilized. In the operation of liquid-liquid extraction columns, the ratio and volume of the heavy and light feeds at any particular instant are usually functions of the efliciency of separation being effected, as judged by the compositions of the extract and raflinate effluents. In a case where ethyl alcohol is being removed from a benzene-alcohol mixture b extraction with water, for example, it may be desirable to obtain a practically benzene-free extract and. therefore, to control the operation of the column by the benzene content of the extract.

For this example the following terminology will be used:

nc=refractive index at 6563 A.

no=refractive index at 5893 A.

nc' refractive index at 4341 A.

d=dispersion, TLG'7ZC Ann and Ad=changes in refractive index and dispersion, respectively The following physical properties are from the International Critical Tables, volume VII:

t C. no 0' i 1.33300 1.33115 1.34035 920 1.30342 1.36062 1.37011 949 Benzene 20 1. 50144 1.40663 1. 52361 2, 608

moment to moment depending on the volume ratio of light to heavy feed. the composition of the benzene-alcohol mixture, etc. On the other hand, the contribution of small amounts of benmight then be expressed by the value zene to the dispersion of the extract would be 5 large relative to the nearly equal dispersions of =25 alcohol and water and would, therefore, provide 31-68-311) zgglfrffilctive means of controlling operation of the l ig sg g f! clgmparmg the Ad va ues co osl This could best be illustrated by calculating the 10 Simngfly, a fi gtg gfcomposmons C and no, Ann, :1 and Ad for each of the compositions D v 1 th t t th t 1 represented by the following conditions of operre 8? s a a grea at an twen y o d in anew crease in benzene content, with a corresponding I increase 1n Ad, would be necessary to produce the A. Extract containing 31 per cent alcohol and no Same n as occasioned y increasing the 81601101 benzene content to 48.3 per cent (composition B). B. Alcohol content increased to give a Ad 10 of A further and important use of dispersion 88 5.0--no benzene a means of measuring or controlling composi- C. Thirty-one percent alcohol plus an m nt f tions is found in the many instances-including benzene to give the same Ad 10 as comc es involving binary mixtures-Where t s position B (=50) difficult, undesirable or impracticable to main- D. Thirty-one percent alc hol plus an a t tain the temperature of the measured fluid conof benzene to give the same Ann as composistant or to measure or compensate for temperation B ture changes. This includes, for example, cases E. Alcohol content increased to give the same W r p ra ur ch n e re rapi nd l r Ann as composition C n benzene Under such conditions it may often be desirable The properties of these compositions are sumi dispersion. i a means of measuqing or marized in the following table: rolling composition, inasmuch as dlSpGISlOIhlS virtually unaffected by temperature, and the dis- Per persion of a substance is, in general, substan- Per cent Ai'lnXlO Adxlm tially independent'of its temperature but prosat? 11K, Benportional to its refractive index at any wave zene length in the region in which the dispersion is measured. 2% g 8 313% g "5], 5 The following data, computed from informa- 135344 44 tion given in the International Critical Tables I $123 8' {3%. 22 05% f (volume VII) shows that the dispersion of a substance is considerably less affected by tem- International Critical Tables, volume v11. perature changes than is its refractive index at At this composition mixture separates into two phones. 40 a particular wave length:

Substance Water 1 2?? fi g 525K111 Benzol Temp. range, 0. 10-10 2a4-30m 22445.0 10. e415 10-30 AnD(=1h 1ll .00800 0.0054 0.02100 0. 01011 0.00005 Ann per o. 10= 15 22 51 44 00 Wave length range A. 6563-5893 5803-4341 6563-6893 6563-5893 6563-5893 Ad =d.,-d 0.00000 0.00000 0.00044 0.0000s 0.00004 Ad per 0. (x10 0.10 0.30 0.83 0. 22 0. 21

Examination of the values in the above table shows that dispersion would be a much more eflective means of detecting small amounts of benzene than would the refractive index at a particular wave length. If, for example, the relative sensitivity to changes in benzene content as measured by dispersion be compared to that measured by refractive index at a single wave length on this basis: that, in the one case (composition B) the alcohol content would have to increase from 31 to 48.3 per cent to give a Ad equal to that resulting from an increase in benzene from zero to 0.28 per cent (composition C), whereas in another case (composition E), the Ann caused by this small amount of benzene would correspond to an increase in alcohol from 31.0 to only 31.68 per cent; the ratio We observe from the above calculations that the change in refractive index per degree for the temperature range noted as compared with the change in dispersion for the wave lengths noted is for water as 15 is to 0.15; for sulfuric acid as 22 is to 0.30; for Z-furaldehyde as 51 is to 0.83; for ethyl alcohol as 44 is to 0.22; and for benzol as is to 0.27. It is, therefore, clearly patent that, at least at times, temperature changes may be dis regarded for measurements or controls made on the basis of dispersion, whereas on the basis of refractive index no considerable temperature change without correction can be tolerated. In such cases the apparatus of Fig. 4 can be used to great advantage.

Bearing in mind that the illustrations and examples are cited merely to indicate possible adapll tations of the invention, it is apparent that the invention will find many commercial applications. It is not limited to use with liquids, but may be used also with gases, as, for example, for controlling the admixture of air and butane, etc.

What I claim is:

1. The process of utilizing changes in the refractive index of a fluid for control purposes which comprises collimating beam of monochromatic light, passing the collimated beam through the fluid and causing the emergent beam to fall in the space between two surfaces adapted for utilization of the light energy impinging thereon. which space in the direction of lateral travel of the beam is not substantially wider than the width of the beam, and as a change in the refractive index of the fluid causes the beam to move from the space to one of the surfaces, causing both surfaces to move in the direction the beam has moved so that the beam again falls in the space between them.

2. The process of utilizing changes in the refractive index of a fluid for control purposes which comprises passing a beam of collimated monochromatic light through the fluid and causing the emergent beam to fall in the space between two surfaces adapted for utilization of the light energy impinging thereon, which space in the direction of lateral travel of the beam is not substantially wider than the width of the beam. and as a change in the refractive index causes the beam to move from the space to one of the surfaces, causing the cells to move so that the beam again falls in the space between them, and as the cells move, bringing about a change in the fluid to restore its original refractive index, and as this is restored, returning the cells to their original position.

3. The process of utilizing for control purposes changes in the dispersion of two beam elements of collimated radiant energy of segregated wave lengths passed through a prism containing a fluid which comprises passing one of the beam elements between two surfaces adapted for utilization of the light energy impinging thereon and as a result thereof causing said surfaces to follow said beam element as the refractive index of the fluid in the prisim changes so that the beam is always between said surfaces, the other element being thereby caused to change its position with respect to a photosensitive surface which is maintained in a flxed relation with the aforesaid two surfaces.

4. The process of utilizing changes in the refractive index of a fluid for control purposes which comprises passing a beam of collimated monochromatic light through the fluid and caus ing the emergent beam to fall in the space between two surfaces adapted for utilization of the light energy impinging thereon, which space is wider than the beam by the amount of lateral travel which the beam will make as it fluctuates within the allowable limits of concentration of the fluid. and as the concentration fluctuates beyond said limits, causing the beam to fall on one of said surfaces and thereby set in motion forces which return the concentration of the fluid to within said limits.

5. The process of utilizing changes in the refractive dispersion of a fluid for control purposes which comprises passing through the fl'uid a beam of collimated light whose radiant energy has been reduced to two segregated monochromatic wave lengths and causing one of the wavelength elements of the beam to fall in the space between two surfaces adapted for utilization of the light energy impinging thereon, which space in the direction of lateral travel of the beam is not substantially wider than the width of the beam; and as a change in the refractive index causes the beam to move from the space to one of the surfaces, thereby causing both surfaces to move in the direction the beam has moved so that the beam again falls in the space between them; and as changes in refractive dispersion result in changes in the angular separation between the wave-length elements of the beam, causing the other wave element to change its point of im pingence with respect to other photosensitive surfaces associated only with this wave-length element, and thereby as the angular separation changes, bringing about a change in the fluid to restore its original refractive dispersion.

6. The process of utilizing for control purposes changes in the dispersion of two beam elements of collimated radiant energy of segregated wave lengths passed through a prism containing a fluid which comprises passing one of the beam elements between two surfaces adapted for utilization of the light energy impinging thereon, and moving said surfaces to follow said beam element as the refractive index of the fluid in the prism changes so that the beam is always between said surfaces, the other element being caused to initiate responses in each of a plurality of other light-sensltive surfaces as the refractive dispersion and thus the relative position of the two beams vary.

7. Apparatus for the utilization of changes in the refractive index of a fluid which comprises a hollow prism adapted to contain the fluid, the prism having faces transparent to radiant energy, two. surfaces adapted for utilization of the light energy impinging thereon, each connected to amplifying means and other means adapted to move both surfaces in the direction of either surface as light falls thereon, and a source of a beam of monochromatic light and means for collimating the light, the pieces of equipment being arranged so that a beam from said source falling on the prism is refracted so as to fall approximately in the space between the surfaces.

8. Apparatus for the utilization of changes in the refractive index of a fluid composed of a hollow prism adapted to contain the fluid, the prism having faces transparent to radiant energy, two surfacesadapted for utilizationv of t. e light energy impinging thereon, each connected to amplifying means, a source of a beam of collimated monochromatic light, the space between the surfaces being wider than the beam by the amount of lateral travel which the beam will make as the concentration of the fluid fluctuates within allowable limits, and means actuated by light falling on either of said surfaces for returning the concentration of the fluid to within said allowable limits.

9. Apparatus for utilization of changes in the refractive dispersion of a fluid which comprises a hollow prism to contain the fluid, the prism having faces transparent to radiant energy, a source of a beam of collimated light whose radiant energy is reduced to two monochromatic wave lengths segregated in the energy spectrum, the beam being directed onto the prism and refracted into two elements of different wave lengths, on opposite sides of one of said refracted elements surfaces adapted for utilization of the light energy impinging thereon with means actuated thereby for causing said surfaces to follow said element so that said surfaces are at all times on opposite sides of said element, and at least one other surface adapted for utilization of the light energy impinging thereon which other surface is maintained in a fixed relation to said first-mentioned surfaces and is in the range of the path of the other beam element.

10. Apparatus for utilization of changes in the refractive dispersion of a fluid which comprises a hollow prism to contain the fluid, the prism having faces transparent to radiant energy, a source of a beam of collimated light whose radiant energy is reduced to two monochromatic wave lengths segregated in the energy spectrum, the beam being directed onto the prism and refracted into two elements of different wave lengths, on opposite sides of one of said refracted elements surfaces adapted for utilization of the light energy impinging thereon with means for utilizing the same to cause said surfaces to follow the element so that said surfaces are at all times on opposite sides of the element, and a plurality of photosensitive surfaces adapted to be intercepted by theother beam element as changes in the fluid cause chan es in the refractive dispersion thereof.

11. The process of utilizing changes in the refractive index of a fluid for control purposes which comprises passing a beam of collimated monochromatic light through the fluid and causing the emergent beam to fall in the space between two surfaces adapted for utilization of the light energy impinging thereon, which space is wider than the beam by the amount of lateral travel which the beam will make as it fluctuates within the allowable limits of concentration of the fluid, and as the concentration fluctuates beyond said limits, causing the beam to fall on one of said surfaces and thereby set in motion a desired force.

12. The process of utilizing changes in the refractive dispersion of a fluid for control purposes which comprises passing through the fluid a beam of collimated light whose radiant energy has been reduced to two segregated monochromatic wave lengths and causing one of the wave-length elements of the beam to fall in the space between two surfaces adapted for utilization of the light energy impinging thereon, which space in the direction of lateral travel of the beam is not substantially wider than the width of the beam; and as a change in the refractive index causes the beam to move from the space to one of the surfaces, causing both surfaces to move in the direction the beam has moved so that the beam again falls in the space between them, and as changes in refractive dlspersion result in changes in the angular separation between the wave-length elements of the beam, causing the other wave element to change its point of impingence with respect to other photosensitive surfaces associated only with this wave-length element, and as the angular separation changes, setting a desired force in motion.

13. Apparatus for the utilization of changes in the refractive index of a fluid composed of a hollow prism adapted to contain the fluid, the prism having faces transparent to radiant energy, two surfaces adapted for utilization of the light energy impinging thereon, each connected to amplifying means, a source of a beam of collimated monochromatic light, the space between the surfaces being wider than the beam by the amount of lateral travel which the beam will make as the concentration of the fluid fluctuates within allowable limits, the amplifying means being connected with control means.

14. The process of utilizing changes in the refractive index of a fluid for control pu poses, which comprises collimating a beam of light containing at least one monochromatic element to produce a beam in which the light rays are at least substantially collimated, passing the collimated light through the fluid and intercepting the refracted monochromatic element by a surface adapted to the utilization of the light energy impinging thereon as changes in the refractive index of the fluid cause changes in the direction of the beam element, and moving said surface as the direction of the beam changes so as to maintain the surface in a substantially constant relation to the beam regardless of the direction of the beam.

15. Apparatus for the utilization, for control purposes, of changes in the refractive index of a fluid, which includes a prism with faces tr ansparout to radiant energy and adapted to conaain the fluid, a source of a beam of monochromatic light which impinges on the prism, means located between said source and said prism for substantially collimating the light beam, two photosensitive surfaces connected individually with means for utilization of light energy impinging thereon, and means operated by said light-utilizing means for maintaining said surfaces in substantially the same relative position to the beam as changes in the refractive index of the fluid cause changes in the refractive index of the beam.

16. Apparatus for the utilization of changes in the refractive index of a fluid which comprises a hollow prism adapted to contain the fluid, the prism having faces transparent to radiant energy, a source of a beam of monochromatic light and means for collimating the light, and two photosensitive surfaces spaced about the width of the beam and positioned so that the beam after being refracted by the fluid falls between them, said surfaces being connected individually through amplifying means to means responsive thereto for moving both surfaces in the direction of either surface as light falls thereon so as to keep the surfaces on opposite sides of the light beam.

17. Apparatus for the utilization of changes in the refractive index of a fluid, comprising a hollow prism adapted to contain the fluid, the prism having faces transparent to radiant energy, a source of a beam of collimated monochromatic light, two photosensitive surfaces spaced about the width of the beam and positioned so that the beam after being refracted by the fluid falls between them, means responsive to light falling on either of said surfaces for moving said surfaces in the direction of the surface affected by the light,

and recording means for moving therewith.

18. Apparatus for the utilization of changes in the refractive index of a fluid, comprising a hollow prism adapted to contain the fluid, the prism having faces transparent to radiant energy. a source of a beam of collimated monochromatic light, two photosensitive surfaces spaced about the width of the beam and positioned so that the beam after being refracted by the fluid falls between them, means responsive to light falling on either of said surfaces for moving said surfaces in the direction of the surface affected by the light, recording means, and in the path of said movement of the surfaces and all means moving therewith, means for initiating action on equipment which restores the fluid to its original concentration.

ROBERT M. PIERSON.

(References on following page) REFERENCES crmn Numm 1,806,198 Hardy May 19, 1931 The following references are 0! record in the 1,939,088 Btyer Dec. 12, 1933 file of this patent: 1,955,315 Styer Apr. 1'7, 1934 UNITED STATES PATENTS 5 2,042,281 l y 1938 N be 2,091,303 Brelstord Am. 31, 1937 um I Name Date 2,113,436 Williams Apr. 5, 1938 1,471,342 Logan 2 1923 2,335,1 3 s it 33, 1943 1,774,961 Buchholz Sept. 2, 1930 Certificate of Correction Patent No. 2,483,102 September 27, 1949 ROBERT M. PIERSON It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 7, line 45, for the word exposed read expected;

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the casein the Patent Ofiice.

Signed and sealed this 24th day of January, A. D. 1950.

THOMAS F. MURPHY,

Am'atant Ooma'uionor of PM.