US2251232A - Method and apparatus for developing film - Google Patents

Description

July 29, 1941. H. w. HOUSTON METHOD AND APPARATUS FOR DEVELOPING FILM Filed Nov. '7, 1938 2 Sheets-Sheet l n9 0Q m mm M m5 N T m o& 3

w ow an Q Q 9 W N9 8. a Q g, A at N i Q R A TTORLNEY July 29, 1941. H. W.HOUSTON METHOD AND APPARATUS FOR DEVELOPING FILM 2 Sheets-Sheet 2 Filed Nov. '7, 1938 WEE-Eu A Tree v5) Patented July 29,1941

METHOD AND APPARATUS FOR DEVELOPING FILM Herbert W. Houston, North Hollywood, Calii'., as-

signor to The Houston Corporation, Los geles, Calif., a corporation of California Application November 7, 1938, Serial No. 239,202

9 Claims.

My invention relates a method and apparatus for developing photographic film.

My invention has as client its principal objects the provision of apparatus for the development of film according to a method wherein the emulsion is developed while in contact with only a limited quantity of a developing solution in sufilcient to completely develop the emulsion. Under such circumstances, as development proceeds, the developing solution adjacent the highlight or heavily exposed portions of the image rather quickly becomes exhausted and development ceases in these portions, but inasmuch as a lesser quantity of developing solution is required by the shadow or lightly exposed portions of the image, development in these portions proceeds long after ceasing in the high-light portions. Thus the lightly exposed portions are developed to an abnormally great degree compared to that to which the heavily exposed portions are developed. Preferably the concentration of the developing solution and the quantity thereof which is in contact with the emulsion during development are adjusted to result in the desired density.

or contrast of the high-light portions of the image when development ceases in those portions and the ensuing time of development is adjusted to result in development of the lightly exposed portions of the image to the desired degree.

When this method of development is followed, it is found that the approximately straight line portion of the H 8: D curve representing the re-, lation between density of image and logarithm of exposure is longer than when the commonly used method of development is employed. The H 8: D curve extends straight to a much lower exposure and, when the emulsion is developed to the same gamma (slope of H & D curve), lies above the H & D-curve for ordinary development. The effect of this improved development is, therefore, similar to a. greatly increased speed of the emulsion plus an extended exposure range. These effects haveproven of great advantage in scenic photography, and photography in various scientific fields, and in sound recording.

One of the objects of my invention is to provide apparatus for continuously developing film, and particularly for continuously developing film acoording to the method above described.

Another object is to provide means for supplying a predetermined limited quantity of developing solution to any portion of the film while it is moving through the apparatus.

Another object is to provide apparatus for developing film according to the method above deing the development period.

scribed in which the developing solution in'contact with the film is prevented from oxidation during development by reason of an inert atmosphere surrounding the film during the development period.

Another object is to provide means for controlling the physical environment of the film dur- Another object is to provide a method of developing film comprising wetting the film with developing solution, removing excess unabsorbed solution from the surface of the film, subsequently conducting the film into a chamber filled with a gas inert to the developing solution, and carrying 'out development of the film while surrounded by the gas by action of the developing solution contained in the film. Another object of the invention is to provide a method and means for sealing the chamber in which development takes place against gas leakage while permitting passage of the film into and out 01' the chamber.

Another object is to provide an efiicient squeegee to remove excess solution from the film.

A further object is to provide in a film processing machine for continuous operation means for varying the duration of one step in the process without altering the others.

Another object is to provide in a continuous film processing machine, means for inserting or removing the film from various baths without affecting the continuity of operation of the machine.

Another object is to provide flexible and convenient driving means for the various parts of a developing machine.

Still another object of the invention is to provide developing apparatus which is efiicient and convenient in its operation.

These and other apparent objects I attain in a manner which will be clear from a consideration of the following description taken in connection with the accompanying drawings, of which:

Fig. 1 is an elevational view, partly in section, of the apparatus of my invention.

Fig. 2 is a sectional view of the apparatus of Fig. 1 taken along the line 2-2, as indicated.

Fig. 3 is a plan view of the apparatus of Fig. 1 with part of the developing cabinet cut away.'=

Fig. 4 is a sectional view of one of the speed changing units employed in driving my apparatus.

Fig. 5 is a sectional view of the unit of Fig. 4 taken along the line 5-8, as indicated.

In my developing apparatus I preferably provide a plurality of tanks in, ll, and 12 which are preferably filled with a developing solution, which may be of similar composition to those ordinarily employed in the art. The developing solution 13 in tank 16 is preferably of different concentration from the developing solution 14 in the tank H which is preferably of different concentration from the developing solution in tank 12. Thus, the three developing solutions may be of increasingly greater concentration each suitable for afilm exposed in a certain manner. If desired, however, the concentration of developer in all of the tanks may be the same. In any case, the apparatus is adapted to submerge continuously moving film into any one Or all of the developing solutions in series or to remove the film from contact with any one or all of the solutions at will. It is also adapted to permit variation of the amount of film in each tank and the speed of passage of the film therethrough. By this means the apparatus is made very fiexible and is adapted to process films of various types and films which have been over-exposed or underexposed as well as those with normal exposure.

Rotatably mounted on a panel l6, which may be supported by the back wall of the tanks I0. I l, and I2, are reels l1 and I8 of exposed perforated film to be developed. The film 20 from reel l1 leads under a roller 2| and over a. sprocket 22 which engages the film perforations and drives the film. The film 20 passes around the roller 23 of the elevator 24 within the tank), out over the driving sprocket 25, over the driving sprocket 26, under the roller of elevator 21 in tank H, over driving sprockets 28 and 30, under the roller of elevator 3| of tank I2 and out over driving procket 32 and roller 33. The elevator 24 includes two bearing portions 34 and 35 at the ends thereof which enclose and fit loosely the rod 36, preferably of rectangular cross-section, which is supported at the bottom on the fioor of tank It! and at the top by a bracket 31 attached to the panel I6. The roller 23 is supported rotatably on the elevator 24 between the bearing portions. A rod 38 is attached to the top of the elevator 24, is slidably supported in the bracket 31, and terminates at the top in a knob 40. The rod 38 serves in manually raising and lowering the elevator 24 and also serves as an indicator of the position of the elevator in the tank. For the latter purpose the rod 38 is notched at regular intervals along its length. The elevators 21 and 3! are identical in construction to the elevator 24, just described, are provided with attached rods 4| and 42, respectively, similar to the rod 38, and slide on stationary rods 43 and 44, respectively. The elevators 24, 21, and 3| are freely movable on the rods 36, 43, and 44 and may be automatically raised and lowered in the respective tanks by means hereinafter described.

In passing through one or more of the tanks 10, I I, and 12, the emulsion of the film absorbs 2. limited quantity of developing solution and generally tends also to carry some free excess solution on the surface of the film. It is desirable to remove this excess solution and leave only that which has been absorbed by the emulsion or exists as a thin uniform coating, and for this purpose I employ a squeegee 45 of novel construction. Adjacent the tank l2 is a vessel 46 with a partition 41 extending down into the tank nearly to the bottom thereof, and carrying a roller 48 at its lower end. The vessel 46 is filled almost to the top with mercury 50 or other suitable liquid which is immiscible in waterand is of density large compared to that of water. The film 20 passes over the roller 33 down into the mercury 50, under the roller 48 and up on the other side of the partition 41 and out of the mercury. As the film moves into the mercury on the entering side of the squeegee 45, the solution clinging to the film tends to rise to the surface of the mercury because of the great difference in density of the two liquids. Then as the film moves lower into the mercury the pressure due to the head of mercury above becomes greater and greater. This pressure is applied uniformly over the film and forces any free excess solution upward into a region of lower pressure, and thence to the top of the tank. The removed developing solution 51 collects on top of the mercury 50 and runs back into the tank l2.

The film 20 rises from the mercury 50 and passes through a conduit 52 which makes a tight joint with the vessel 46 and partition 41 on the outgoing side of the squeegee. Supported on the conduit 52 is a vibrator 53 operated electrically and carrying a roller 54 which bears on the film. The operation of the vibrator causes the roller 54 and consequently the film 20 to be constantly vibrated with a small amplitude sufficient to loosen any small droplets of mercury which may be clinging to the film. When a liquid alloy of mercury and lead, or mercury and tin, or mercury and other suitable metal, which alloy is less fluid than mercury, is employed as the liquid 50 in the squeegee 45, it is found that the liquid does not cling to the film or in the perforations as is the case when mercury alone is used, and such a composition has been found advantageous to use.

After passing through the conduit 52, the film 20 passes over a roller 55 located in an elbow 56 which makes a tight joint with the conduit 52 and a developing cabinet 51 into which the film 20 passes through a hole 58. The film comes to the developing cabinet with it emulsion wet with developing solution, but with hardly any development having taken place in the tanks l0, H, and I2 because of the relatively short time permitted in these tanks. It is desired to develop the emulsion by action of only the limited quantity of developing solution absorbed by the emulsion and to this end the film is kept for a relatively long time out of contact with any source of developing solution but with the absorbed solution still in the emulsion. This development step occurs while the film is in the developing cabinet 51. To protect the absorbed developing solution against oxidation and resultant deterioration which would result in the presence of air, the cabinet 51 and its connections are preferably made substantially gas tight and the chamber within the cabinet is filled with an inert gas, for example, nitrogen or helium, which has no effect upon the developing solution or the film.

The cabinet 51 may comprise a box-like structure of rectangular cross-section with double walls and thermal insulation 60 between the walls. Two doors 6| may be provided which, when open, expose substantially the whole interior of the cabinet, and which may be locked to seal the cabinet by latches 62. The temperature within the cabinet 51 may be controlled by means of pipes 63 which pass through the cabinet in a circuitous path and are adapted to carry cooling fiuid such as brine which may be circulated through suitable well-known refrigerating equipment 64 which acts in response to the thermostat .88 within the cabinet to maintain constant the temperature in the cabinet 51.

Inert gas. preferably nitrogen, is contained under pressure in a tank 88 and is admitted to the interior of the cabinet 51 through a reducing valve 81 and a pipe 88. A vent pipe 18 controlled by a valve 1I connects with the interior of the 'shafts 13 which extend across the cabinet at the top thereof. Each of the shafts 13 is rotatably supported at each side of the cabinet 51 in bearings 14, and passes out through the cabinet to connect with the driving means. Disposedalternately with the shafts 13 along the cabinet are the shafts mounted similarly to the shafts 13 and having sprockets 18 attached on the ends thereof opposite to the ends of shafts 12 to which sprockets 12 are attached. On each of the shafts 13 are mounted a plurality" of rollers 11 which may turrion'the shafts 18, and on each of the shafts 15 are mounted a plurality of rollers 18 which may turn thereon. Near the bottom of the cabinet are a plurality of transversely extending stationary shafts 88 on each of which are rotatably mounted a plurality of rollers 8|. The film 28 passes over the first sprocket 12, vertically downward and under one of the rollers 8I, up and over one of the rollers 11, down and under a roller 8 I, and so on, until it passes under the last roller 8I on that particular shaft. The film then passes up over the driving sprocket 18 on the adjacent shaft 15, down and under the corresponding roller 8|, up over a roller 18, and so on. until it has passed under the last roller 8| on that shaft. The film then passes up over the sprocket 12 on the adjacent shaft 13 and proceeds in this zigzag manner through the cabinet 51. At the outgoing end of the cabinet 51 the last roller 8i is omitted from its shaft 88 and the roller 82 is substituted therefor, which roller is mounted rotatably on an elevator 83 which slides on a vertical rod 84 of square cross-section mounted within the cabinet 51. Near the outgoing end the film 28 passes over rollers 18 on the shaft 15 and under rollers 8I,

then passes over the next to the last roller 18, down and under the roller 82, up and over the last roller 18, and out into the elbow 85. A conduit 88 connects with the elbow 85 and leads to a mercury seal 81 containing mercury 88 and constructed similarly to mercury squeegee and seal 45. The film 28 passes over a roller 88, under a roller 9I in the mercury seal 81, out of the mercury, over a roller 82, and over a driving sprocket 93. It is evident that where the film first comes into the inert gas, the gas is also sealed against leakage by the mercury squeegee 45 so that the interior of the developing cabinet 51 is completely sealed from the atmosphere without. The conduit 88 is provided with a door 84 which may be opened to facilitate threading the machine. A pressure gauge 85 connects with the interior of the conduit 86 to measure the pressure within the developing cabinet 51. Since the interior of the cabinet is completely sealed, the gas within soon becomes saturated with moisture and no further evaporation of water from the film takes place in the cabinet 51. This is a desirable condition, but if desired, the gas within the cabinet may be circulated through humidity control apparatus of well-known construction to maintain the relative humidity within the cabinet 51 at any desired value.

An auxiliary developing tank 86 containing developing solution is provided in which the film may be submerged for a short period of ordinary development if it should be found that the highlights of the scene need more development. Th tank 88 is provided with an elevator 81 having an indicating rod 88 similar in construction t the elevators 24, 21, and 8|; For convenience in determining the state of development of the film an inspection lamp 98 is preferably located under the film 28 and is adapted to be turned on and off as desired. Following tank 88, I provide a tank I88 containing acid stop and hardening solution I8I which may be of a compositio similar to those well-known in the art. Following the tank I88 is a tank I83 which may co tain fixing lution such as is well-known in th art, and f0 owing tank I83 is a tank I84 containing wash water. The film 28 passes over driving sprocket 93, under the roller of the elevator 91, and over the driving sprocket I85,

- Over each of the tanks I88, I83, and I84 are rotatably mounted a plurality of rollers I88 on the same shaft, and within each of the tanks one or more rollers I81, in number one less than the number of rollers I88, is weighted by a weight I88 and hangs on the film loop within the tank. After passing over sprocket I the film passes over one of the rollers I88 down into the tank I88, under the roller I81, up over the other of rollers I86 and on through the tanks I83 and, I84 in similar manner. After passing out of the wash tank I84, the film 28 may go on through a dry-box, not shown, but constructed in a wellknown manner, for the purpose of drying the film, following which the film is wound upon a reel.

For the purpose of driving the various parts of the machine I employ an electric motor II8 which connects through a variable speed transmission III with the shaft II 2. Geared to the shaft II2 through suitable bevel gears H3 is the shaft H4 to which is attached the driving sprocket I85. Connected through bevel gears IIIi with the shaft I I2 is the driving shaft of a speed change unit I IS, the driven shaft of which carries the sprocket 93. The driven shaft of the speed change unit H8 and the shaft II4 are supported in bearings mounted on the panel I I1 which may be attached to the adjacent tanks for support.

The speed change unit II6, which is employed in several places in the apparatus, is constructed as illustrated in Figs. 4 and 5, in which it is shown as connected to drive the sprockets of tanks I8, II, and I2. It comprises a housing I I8 into which projects at one end a driving shaft I28 and at the other end a driven shaft I2I in alignment with the shaft I28. Keyed to the shaft I28 within the housing H8 is a gear I22 of relatively large pitch diameter. Rotatably supported in the housing H8 is another shaft I23 carrying a gear I24 keyed thereto, of small pitch diameter relative to the gear I22, and meshed with the gear I22. Keyed to the other end of the shaft I23 is a gear I25 which meshes with another gear I26, preferably of the same pitch diameter, which is mounted rotatably on the shaft I2I. The gears I22 and I26 have radial clutch teeth I21 and I28, respectively, which are adapted to mesh, respectively, with corresponding teeth I 38.and I3I on the opposite ends of a movable clutch member I32 which is adapted to slide on the shafts I28 and I2I and which is keyed for rotation with the driven shaft I2I but can rotate freely on the shaft I20. The member I32 is provided with a peripheral track I33 in which ridesa pin I34 attached to a lever I35 which is connected for rotation with the shaft I36 which passes through the housing H8 and is connected to a lever I31 for controlling the movement of clutch member I32. When the member I32 is slid over into engagement with the teeth I21, the shafts I20 and I2I will be directly coupled. When the member I32 is in the intermediate position shown in Fig. 4, in which it engages neither teeth I21 nor teeth I28, the two shafts I20 and I2I are entirely disconnected. And when the member I32 is slid over into engagement with the teeth I28, the shaft I20 drives the shaft I2I at increased speed through gears I22, I24, shaft I23, gears. I25, I26, teeth I28, I3I, and member I32. Preferably the various gears are so proportioned as to result in shaft I2I rotating at about double the speed of shaft I20 when the unit is set for increased speed of shaft I2I.

As employed in driving the sprocket 93, the lever I31 is connected by link I38 with one end of a hand lever I40 pivotally supported at I41 on the panel II1. Pushing in the hand lever I40 results in setting the speed change unit II6 so as to result in the sprocket 93 traveling at the same speed as the incoming shaft of the unit II6. When the lever I40 is in an intermediate position the sprocket 93 will remain at rest. When the hand lever I40 is pulled all the way out, the sprocket 93 rotates at twice the- I43 are attached for rotation therewith. Mounted in bearing supports I39 and I49 opposite the shafts 13 and 15 is a shaft I44 to one end of which, above the sprocket I43 is attached for rotation therewith a chain sprocket I45. A chain I46 is in mesh with both sprockets I43 and I45. The shaft I44 drives the shafts 13 and 15 through the bevel gears I41 and I48, respectively.

Located opposite to the shafts of sprockets 22, 25, 26, 28, 30, and 32 is a shaft I50, at one end of which, under the sprocket I42, is attached for rotation with the shaft I50 a chain sprocket II, and in mesh with both of the sprockets I42 and I5I is a chain I52. The shaft I50 drives the film sprocket 32 through bevel gears I53. The shaft- I50 connects with a speed change unit I I6, forming the driving shaft therefor. The driven shaft I54 of this speed unit drives film sprockets 28 and 30 through' bevel gears I55 and I56 and forms the driving shaft for another speed change unit H6. The driven shaft I51 of this unit drives film sprockets 25 and 26 through bevel gears I58 and I60, respectively, and forms the driving shaft for another speed change unit II6. This last speed change unit has a driven shaft which drives film sprocket 22 through bevel gears I6I. The housings of the speed change units II6 are mounted on a shelf I62 supported by the panel I6. Hand levers I63, I64, and I65 are pivotally mounted at I66, I61, and I68 on the face of panel I6 and are at their ends connected, respectively, to levers I31 of the three speed change units II6 by links I10, HI, and I12, respectively.

It will be apparent that when any one of the hand levers I63, I64, and I65 is pushed in to extreme position it will result in the driven shaft, on the left side of the corresponding speed change the driving shaft of that unit. when any one of these levers is in intermediate position the driven shaft of the corresponding speed change unit is at rest and all the sprockets driven by that unit and to the left thereof are at rest. When any one of the hand levers is pulled out to extreme position, the driven shaft of the corresponding speed change unit III rotates with double the speed of the incoming shaft and the sprockets driven by this unit and all to the left thereof rotate at double speed provided the speed change units to the left thereof are set for the same speed of driving and driven shafts. Needless to say, the gear and chain sprocket ratios throughout the apparatus are such that when all speed change units are set for the same speed of driving and driven shafts, all of the film driving sprockets throughout the machine rotate with the same speed. The driving mechanism described above provides a flexibility of control of the movement of him through the machine which results in very efficient and convenient operation thereof.

In the operation of the machine, a leader is first threaded through and the film 20, which is to be developed, is attached to the end thereof. With the doors 6I closed, the vent valve H is opened and inert gas is permitted by control of valve 61 to enter the cabinet 51 and flush out unit H6, in Fig. 3, running at the same speed as all air in the cabinet. The valve H is then closed and the valve 61 is preferably adjusted to allow a small inflow of gas into the cabinet sufficient to produce and maintain a pressure within the cabinet slightly above atmospheric pressure so as to prevent oxygen from the air outside from entering the cabinet. The refrigerating system is operated until the desired temperature within the cabinet is attained. It is assumed that, in accordance with common practice, tests have been made on small sections of the various scenes of the film to be developed and it has been determined what type of development is required on each of the various scenes in order to secure the best effect. Assume that the machine has been threaded so as to result in the set-up as illustrated in Fig. 1 and that the first scene requires the development that results from this set-up.

The machine is started by energizing the motor 'IIO. As the film 20 moves through the developing solution I3 in the tank I0, the emulsion absorbs a limited quantity of developing solution determined by the concentration of the solution and by the time the film takes in passing through tank I0. After passing through the tank I0, the film 20 passes through the mercury squeegee and seal 45 where its excess developing solution is removed. It then enters the developing cabinet 51 where development of the image takes Place by action of only the limited quantity of developing solution contained in the emulsion. During development the developing solution in the emulsion is protected against oxidation by the environment of inert gas through which it passes. The duration of the development period is determined by the speed of the film which is controlled by the variable speed transmission II I. The film then passes out of the cabinet 51 through the mercury seal 81, through the hardening solution IIII in tank I00, through the fixing bath in tank I03, is washed in tank I04, and is dried as in ordinary practice.

As the developed film first passes over the inspection lamp 99, the lamp may be lit and the film inspected. Should it be found that any furtion resulting in sprocket 92 traveling with twice.

the speed of the other sprockets. Film will begin to accumulate between the sprockets 93 and I and the weight of the elevator 91 will cause it to sink into the tank 96 taking the film with it and submerging it in the solution. Since the film still travels at the same speed in the cabinet 51, the increased length of film between sprockets 93 and I05 necessitates a shortened length of film between the sprocket 93 and the last sprocket in the cabinet 51. This shortened length of film is made possible by the action of the elevator 83 within the cabinet 61 which automatically is raised by film tension as the elevator 91 descends in the tank "96. When the elevator 91 has descended into the tank 96 a sufficient distance to result in the film being in the auxiliary developing tank 96 for the desired length of time, the hand lever I40 is pushed to the extreme inward position whereupon the sprocket 93 again rotates at normal'speed and elevators 91 and 69 remain suspended in the positions they occupy at the time of shifting.

When the next scene appears, if it is desired to remove the film from the auxiliary developing tank 96, the hand lever I46 is pulled out to intermediate position, stopping sprocket 93. The sprocket I05 continues rotating and quickly takes up the film in tank 96, raising the elevator 91. coincidentally slack appears in back of the sprocket 93 which is taken up by the descending elevator 83. When the film has been lifted out of the solution in tank 96 the hand lever I40 is again thrown to extreme inward position and all the film continues at normal speed.

In order to permit change of the quantity of developing solution absorbed by the emulsion, I preferably make the developing solution in the tank II more concentrated than that in the tank I0, and that in the tank I2 more concentrated than that in the tank II. Should it be desired, then, to increase the quantity of developing solution absorbed by the emulsion it is only necessary to shift the film from tank I0 to tank II or to tank I2. Shifting from the tank ID to the tank II may be accomplished by pulling hand lever-I64 out to its extreme position, causing sprockets 26, 25, and 22 to all rotate with double the speed of sprocket 28. Film will therefore accumulate between the sprockets 26 and 28 and the weight of the elevator 21 will submerge the film in the tank II. When the film has been submerged to the desired level as indicated on the rod II, the hand lever I 64 is thrown to its extreme inward position and all sprockets rotate at normal speed. The hand lever I63 is then pulled out to intermediate position, stopping the sprocket 22, whereupon the film in the tank I0 is quickly taken up and the elevator 24 is raised out of the tank I0 by film tension. When the film is out of the solution in the tank III, the hand lever I63 is pushed to its extreme inward position and all sprockets rotate with normal speed. The film has in this manner been shifted from the tank I0 into the tank I I. It will be clear. how a similar operation of the hand lever I65 instead of the hand lever I64 would result in shifting the film from the tank In into the tank I2. It is also apparent that if the film .is

not raised out of the tank II, but is submerged in the other tanks as above described, it is possible to run the film through two or all three tanks, if desired, and by stopping the descension or elevation of the elevators in the various tanks the time taken by the film in passing through the respective tanks may be varied at will.

Assuming the film submerged in the tank II and lifted out of the tank II, if it is desired to shift the film back to the tank II, the hand lever I6; is pulled to its extreme outward position,

causing the sprocket 22 to travel with double speed, whereupon accumulates between the sprockets 22 and 26 and the elevator 24 descends, submergingth'e film in the tank Iii. When the film has been submerged to the extent desired the hand leverl63 is thrown to its extreme inward position, whereupon all sprockets rotate at normal speed. To lift the film out of the tank II thehand lever I94 is thrown to intermediate position in which the sprockets 22, 25, and 26 are all stopped. The continued rotation of the sprocket 29 then takes up the film in the tank I I and causes the elevator 21 to be raised. When it has risen to the desired level the hand lever I 64 is thrown to the extreme inward position in which all sprockets again rotate at normal speed.

If it is desired to change the time of development within the developing cabinet 61, the speed of the film is changed by means of the variable speed transmission III, and it will be obvious that the lengths of film undergoing processingin the various other steps of the process can be readjusted to maintain the time of processing in these other steps the same as it was prior to changing the film speed. It will be apparent that my apparatus provides flexibility of control of the duration of the various steps of the film processing while the film is continuously being processed.

If desired, the shifting of the various levers for the purpose of controlling the various steps of the process, normally performed manually, may be done automatically by provision of suitable electric relay means energizing suitable electromagnetic switching apparatus in response to notches or other preformed marks on the film 29 in a manner somewhat similar to that in which printing lights are changed in the continuous printing of motion picture film.

While I have shown a developing apparatus having provision forthe processingof only one length of film at a time, it is understood that the apparatus may be adapted, by change in proportions and provision of additional driving sprockets and rollers, etc., to accommodate a plurality of separate lengths of film which can be processed simultaneously. It is fm'ther understood that various other changes and modifications in design and construction of my apparatus and in the method herein disclosed may be made by those skilled in the art without departing from the spirit and scope of the invention defined in the appended claims.

I claim as myinvention:

1. The method of developing film comprising: wetting said film with a developing solution to cause absorption of said solution by 'said film; removing excess unabsorbed solution from the surfaceof said film; subsequently conducting said film into a chamber filled with gas inert to said developing solution; and carrying out substantially the entire development of said film while surrounded by said gas by action of the developing solution contained in said film.

2. Apparatus for developing film comprising,

a developing solutionlto cause absorption of said solution by said film; a chamber filled with gas inert to said developing solution; and means for passing the film containing developing solution through said chamber, whereby development of said film takes place in said chamber.

3. Apparatus for developing film comprising, in combination: a tank containing developing solution; a developing chamber filled with gas inert to said developing solution; and means for moving said film first through said developing solution and then through said developing chamber.

4. Apparatus for-developing film comprising, in combination: a tank containing developing solution; a developing chamber filled with nonoxldizing gas; sealing means for said chamber adapted to substantially prevent the escape oi gas but permit passage of said film therethrough; and means for moving said film successively throughsaid' developing solution and through said developing chamber.

5. Apparatus for developing film comprising, in combination: means for wetting said film with a developing solution to cause absorption of said solution by said film; means for varying the quantity of solution absorbed by said film; a developing chamber filled with gas inert to said developing solution, sealing means for said chamber adapted to substantially prevent the escape of gas but permit passage of said film therethrough; and means for moving said film containing developing solution through said developing chamher.

6. Apparatus for developing film comprising, in combination: a tank containing developing solution; a developing chamber filled with inert gas; means for supplying inert gas to said de veloping chamber; sealing means for said chamber adapted to substantially prevent the escape of gas therefrom but permit passage of said film therethrough; means for moving said film successively through said developing solution and through said developing chamber; means for changing the length of film in said tank; and means for changing the velocity of said film.

7. Apparatus for developing film comprising, in combination: a tank containing developing solution; a developing chamber sealed from the atmosphere; means for supplying said chamber with gas inert to said developing solution; an entrance conduit for said film leading into said developing chamber; a vessel containing liquid sealing said entrance conduit, said liquid being immiscible with water and of density large compared with that of water; and means for successively moving said film through said tank, downward into said liquid, out of said liquid into said entrance conduit, through said entrance conduit, and into said chamber.

8. In film processing apparatus, the combination of: a plurality of film processing baths; means for moving said film successively through said baths including an entering film driving sprocket and an outgoing film driving sprocket associated with each of said baths; means acting by gravity on the film between said sprockets associated with each of said baths tending to submerge said film in said baths; and means for simultaneously changing by the same amount the speed of rotation of the entering sprocket associated with any selected bath and of all the film driving sprockets associated with preceding baths, without changing the speed 01 rotation of the outgoing sprocket of said selected bath.

9. In film processing apparatus, the combination of: a first film processing bath; a second film processing bath; means for moving said film successively through said first and second baths including an entering film driving sprocket and an outgoing film driving sprocket associated with each of said baths; means acting by gravity on the film between the sprockets associated with each of said baths tending to submerge said film in said baths; a driving shaft connected to rotate the outgoing sprocket associated with said second bath; a second shaft connected to rotate said entering sprocket associated with said second bath and said outgoing sprocket associated with said first bath; a third shaft connected to rotate said entering sprocket associated with said first bath; a speed change device driven by said first shaft and driving said second shaft; a second speed change device driven by said second shaft and driving said third shaft; each of said speed change devices providing means for changing the speed of rotation of the shaft which it drives relative to the speed of rotation of the shaft which drives it.

HERBERT W. HOUSTON.

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