Control For Mixing Fluids Of Different Specific Gravity

Abstract

A hydrometer-actuated control for mixing dampening fluid comprising water and other chemical ingredients mixed with alcohol to be applied to the plate of a lithographic printing press. The control device comprises a mixing chamber, in which alcohol and dampening fluid are mixed, adapted to remove air bubbles therefrom; a test chamber having a hydrometer freely floating in a sample solution drawn from the mixing chamber; and an electrical conductor on the hydrometer which moves with the hydrometer relative to the surface of the sample solution to actuate a relay to open and close a solenoid operated valve to regulate flow of alcohol to the mixing chamber.

Description

BACKGROUND OF THE INVENTION

In a dampening device for transferring dampening fluid to the plate of a lithographic offset printing press, a pan roller is rotated through dampening fluid in a pan and a film of fluid on a pan roller is transferred to the printing plate.

U.S. Pat. No. 3,259,062 to Harold P. Dahlgren teaches that a water soluble, volatile, organic liquid, such as a volatile alcohol mixed with water is a very effective dampening fluid for use in lithographic printing. However, the volatile fluid, exposed to the atmosphere, evaporates readily and the optimum ratio of alcohol to water is difficult to maintain in the system.

U.S. Pat. No. 3,352,317 to Harold P. Dahlgren on "Dampening Fluid Cooling And Circulating Apparatus For Lithographic Offset Press Dampening Device" teaches that when a new batch of volatile fluid is added to the fountain of a dampening system to be circulated through the pan, the fluid does not readily mix with the dampening fluid therein. The added dampening fluid changes the proportions of the ingredients of the dampening fluid, which changes the chemistry thereof, and will therefore affect the quality of the printing produced by the press until such dampening fluid has become thoroughly mixed, which usually requires a considerable length of time. The said patent also points out that the temperature of the dampening fluid should be maintained below 75.degree. to prevent emulsification of the dampening fluid with the ink and to reduce oxidation of the plate which is contacted by the dampening fluid.

The objects of the devices disclosed in the before-mentioned patents were to provide an improved dampening fluid with storage and circulation system which diffuses and mixes the dampening fluid and to maintain the temperature of the dampening fluid at a predetermined optimum value. The method and apparatus described therein is a significant improvement over the prior art. However, the devices did not include means for automatically regulating the specific gravity of the dampening fluid to compensate for ingredients of the fluid which are depleted and for evaporation of volatile fluid from the dampening fluid as the fluid was circulated through the system. The device may also be employed to replace any fluid which is depleted or consumed in use.

No simple device heretofore developed had the capability of automatically injecting desired amounts of volatile fluid into the dampening fluid for accurately maintaining the specific gravity of the dampening fluid within reasonable limits.

Specific gravity regulating apparatus heretofore developed have attempted to use a hydrometer floating in liquid to actuate devices for controlling specific gravity of the liquid. However, these devices have provided an imperfect solution to the problem because attempts have been made to employ force exerted by the hydrometer to close contacts in electrical circuits through various mechanical arrangements.

No hydrometer actuated control device heretofore developed has employed a freely floating hydrometer to automatically control the specific gravity of the liquid in which it is floating.

A hydrometer is a very sensitive instrument, the accuracy of which is materially affected by application of external forces thereto.

High flow rate of fluid through a chamber or receptacle in which the hydrometer is floating affects the depth to which the instrument sinks in the liquid.

Air bubbles in the liquid being tested also adversely affect the accuracy of a hydrometer.

Another major difficulty encountered heretofore has resulted from the fact that the sample solution being tested was drawn from a relatively large reservoir and fluid was injected directly into the large reservoir of fluid. In such devices, an excessive amount of fluid is injected into the reservoir before a control system, sampling the reservoir solution, detects a change therein, particularly in situations where the fluid being injected and the fluid in the reservoir do not mix readily.

SUMMARY OF THE INVENTION

I have developed a device for controlling the specific gravity of dampening fluid or other liquids which employs a freely floating hydrometer. Air bubbles are removed from a sample of the liquid and low velocity flow is maintained during testing to provide maximum accuracy.

A primary object of the invention is to provide a control for mixing dampening fluid which uses a hydrometer for controlling the specific gravity of the fluid wherein no appreciable external force is exerted upon the hydrometer.

Another object of the invention is to provide a control for mixing dampening fluid in which fluid injected into fluid circulating from a reservoir is thoroughly mixed in a mixing chamber and a sample of the resulting solution is immediately tested thereby eliminating the possibility that excessive amounts of fluid will be injected into the reservoir solution.

A still further object of the invention is to provide a control for mixing dampening fluid particularly adapted for use in combination with a dampening fluid cooling and circulating apparatus for lithographic offset press dampening devices.

A still further object of the invention is to provide a control for mixing dampening fluid incorporating a venturi in a fluid circulating system for drawing a second fluid into the fluid normally circulated through the system.

A still further object of the invention is to provide a control for mixing dampening fluid having a high degree of accuracy, which is adjustable and inexpensive to construct and use, making the use thereof economically feasible.

Other and further objects of the invention will become apparent upon referring to the specification and drawings annexed hereto.

DESCRIPTION OF THE DRAWINGS

Drawings of the preferred embodiment of the invention are provided so that the invention may be better and more fully understood, in which:

FIG. 1 is a diagrammatic view of the invention illustrating the cooperative relationship between the control device and dampening fluid cooling and circulating apparatus;

FIG. II is a top plan view of the invention with parts broken away to more clearly illustrate details of construction;

FIG. III is a cross-sectional view taken along lines III-III of FIG. II;

FIG. IV is a cross-sectional view taken along lines IV-IV of FIG. III;

FIG. V is a perspective view of the back of the control device with parts broken away to more clearly illustrate details of construction;

FIG. VI is a cross-sectional view taken along lines VI-VI of FIG. III;

FIG. VII is a cross-sectional view taken along lines VII-VII of FIG. III; and

FIG. VIII is a diagrammatic view of a modified form of the invention.

Numeral references are employed to indicate the various parts shown in the drawings and like numerals indicate like parts throughout the various FIGS. of the drawings.

DESCRIPTION OF A PREFERRED EMBODIMENT

Referring to FIG. I of the drawings, the numeral 1 generally designates the body of the control device having a tubular mixing chamber 2 and a tubular control or test chamber 4 connected by a passage 6.

One end of conduit 10 is connected to a circulating system 8 through which electrically conductive fluid circulates as will be hereinafter more fully explained and the other end of conduit 10 is connected to a venturi 12. A conduit 14, connected through normally closed valve 16 and conduit 15, communicates with fluid supply source 18 such that when valve 16 is opened fluid is drawn from supply source 18 through conduit 14 by the partial vacuum at the throat of venturi 12.

The outlet of venturi 12 communicates with inlet 20 of mixing chamber 2.

An overflow tube 22 in mixing chamber 2 has its lower end connected through outlet 24 to a conduit 26 which returns fluid to the reservoir 101 of circulating system 8.

A test chamber outlet passage 30 communicates with the inside of test chamber 4 at a position slightly below the elevation of the upper end of overflow tube 22 in mixing chamber 2. Crossover passage 6 between mixing chamber 2 and test chamber 4 is of smaller diameter than test chamber outlet passage 30 to maintain the fluid level in test chamber 4 at a substantially constant elevation.

From the foregoing it should be readily apparent that a portion of the fluid flowing through circulating system 8 passes through conduit 10, venturi 12 and inlet 20 into mixing chamber 2. A major part of the fluid entering mixing chamber 2 flows downwardly through overflow tube 22, outlet 24 and conduit 26 into the reservoir 101 of circulating system 8.

A sample of the fluid in mixing chamber 2 passes through passage 6 into test chamber 4, and through test chamber outlet 30 to be returned to the circulating system 8.

A conventional hydrometer 40 is disposed within test chamber 4 and floats in a sample solution 5 contained therein. The hydrometer is a well-known device for measuring the density or specific gravity of liquids. It consists of a long slender glass float weighted at the lower end and has a graduated scale on the slender neck portion such that the specific gravity of the liquid is indicated by the depth to which the instrument sinks therein.

An isolated solution receptacle 42 is disposed within the test chamber 4 and has isolated solution 44 contained therein. The wall 43 of isolated solution receptacle 42 is made of electrical insulator material and is electrically insulated from the sample solution in test chamber 4.

A conductor 46 is secured about the stem 40a of hydrometer 40 and opposite ends thereof extend into test chamber 4 and insulated receptacle 42 in position to contact the liquid therein.

An electrode 50, extending through the wall of test chamber 4, is submerged in sample solution 5 contained therein and electrode 52, extending through the wall of test chamber 4 into receptacle 42, is submerged in the isolated solution 44 contained therein. Electrode 50 is connected through line 54 to a current responsive switching device, such as the coil 56 of a single pole double throw relay 58. The other end of coil 56 of relay 58 is connected through line 60 to one side of the secondary winding 62 of a transformer 64. Electrode 52 in isolated solution receptacle 42 is connected through line 66 to the secondary winding 62 of transformer 64.

The primary side 68 of transformer 64 is connected through lines 70 and 72 to the electrical lines 74 and 76, respectively, which are connectable to a conventional source of electricity.

From the foregoing it should be readily apparent that when hydrometer 40 sinks into sample solution 5 in test chamber 4, causing the end 47 of conductor 46 to engage the sample solution, an electrical circuit is completed from electrode 50 through the sample solution 5 in test chamber 4, through conductor 46, isolated solution 44, electrode 52, line 66, secondary winding 62, line 60, coil 56, line 54 to electrode 50. Therefore, when the end 47 of conductor 46 on hydrometer 40 engages the surface of the sample solution 5 in test chamber 4, coil 56 of relay 58 is energized.

Line 74, connectable to an external power supply (not shown), has a switch 78 therein. When switch 78 is closed electrical current is delivered through lines 70 and 72 to primary winding 68 of transformer 64.

Line 74 is connected to electro-magnetically actuated switch 56a of relay 58 in series with switch 78.

Relay 58 is of conventional design and in the particular embodiment of the invention illustrated in the drawing the fluid in fluid supply source 18 is alcohol having a specific gravity lower than that of the fluid which flows through circulating system 8.

Movable pole 56a of relay 58 is spring biased to the closed position so that alcohol will flow from fluid supply source 18 when the specific gravity of the fluid flowing through circulating system increases, causing hydrometer 40 to move upwardly, disengaging the end 47 of contact 46 from the surface of the sample solution 5 in test chamber 4. When a sufficient quantity of alcohol has been added hydrometer 40 will settle in the sample solution, causing end 47 of contact 46 to engage sample solution 5, completing a circuit, energizing coil 56 of relay 58, thereby opening switch 56a to stop the flow of alcohol.

Lines 74' and 76 are connected to solenoid device 80 which is operably connected in conventional manner to valve 16.

It should be appreciated that when switch 78 in line 74 is closed and switch 56a of relay 58 is closed a circuit is completed through solenoid device 80 to line 76 to open valve 16. When valve 16 is opened fluid is drawn from container 18 through line 14 into venturi 12 to be mixed with the fluid flowing through circulating system 8 in line 10.

A pilot light 82 is connected to lines 74' and 76 through lines 83 and 84, respectively, in parallel with solenoid 80. Pilot light 82 is illuminated when solenoid 80 is energized, thereby indicating that valve 16 is open and that fluid is flowing from supply source 18.

Referring to FIG. V of the drawing, the body 1 of the control device is preferably cast or molded as an integral unit, having mixing chamber 2, test chamber 4, passage 6, venturi 12, inlet passage 20, outlet passage 24, and test chamber outlet passage 30 formed in the body 1 of the control device by positioning suitable cores within a mold to be filled with molten material such as polyester resin.

While it is not absolutely necessary that the body 1 of the control device be cast as an integral unit having passageways formed therein, it is desirable to do so for several reasons. It should also be noted that while it is not absolutely necessary that the body 1 be constructed of material which is an electrical insulator, such construction offers several material advantages.

Casting body 1 as an integral unit minimizes leakage of fluid which is circulated therethrough and reduces construction costs resulting from savings in material and labor. It is also desirable that the walls of mixing chamber 2 and control chamber 4 be transparent, allowing visual inspection of the operation of the device.

Construction of the body 1 of a material which is a good electrical insulator assures that electrical current cannot flow from electrode 50 in mixing chamber 4 to electrode 52 in isolated solution receptacle 42 except through conductor 46 when the end 47 thereof is in contact with the sample solution in test chamber 4. A short circuit between electrode 50 and electrode 52 makes the device inoperable. If the body 1 of the control device is constructed of a material which is a conductor of electricity insulation 43 must be provided as illustrated in FIG. III.

It is desirable that passage 6 connecting mixing chamber 2 and test chamber 4 have a smaller cross-sectional area than overflow tube 22 and test chamber outlet passage 30.

As best illustrated in FIG. VII, fluid entering the control device through conduit 10 circulates through inlet 20 into mixing chamber 2. The end 20a of inlet passage 20 is substantially tangentially disposed relative to the inner surface of tubular mixing chamber 2 which imparts a churning, agitating motion to the fluid therein to thoroughly mix the fluids from conduits 10 and 14. Centrifugal force of the swirling liquid causes air bubbles to be moved toward the center of the chamber allowing them to move upwardly through the liquid about tube 22 away from passage 6.

Fluid which passes through passage 6 is thoroughly mixed and is free of air bubbles. The flow rate of liquid through passage 6 is small relative to the flow rate of liquid through inlet 20. The majority of the liquid entering mixing chamber 2, through inlet 20, is discharged through overflow tube 22. For example, diverting 15 percent of the fluid which enters mixing chamber 2 into test chamber 4 through passage 6 will normally provide adequate solution for sampling without causing excessive turbulence to disturb the free floating condition of hydrometer 40.

The percentage of fluid to be diverted through passage 6 into test chamber 4 may vary depending upon the flow rate of fluid through circulating system 8 and the quantity of fluid passing through conduit 10. A primary consideration governing the flow through the test chamber is to maintain forces of the fluid on the hydrometer resulting from motion of the sample of fluid within desired limits.

It is desirable that control chamber outlet passage 30 be larger than passage 6 to assure that the surface of the sample solution in control chamber 5 be maintained substantially constant. A tubular restrictor 41 extends upwardly from the bottom of control chamber 4 to disperse the jet of liquid flowing into the control chamber to minimize the force exerted by the liquid on hydrometer 40.

Conductor 46, best illustrated in FIG. III, may be constructed of any suitable material which is a good conductor of electricity. However, to minimize interference with the freely floating condition of hydrometer 40 it is desirable that conductor 46 be very lightweight. In the particular embodiment of the invention illustrated in the drawing, conductor 46 is a very thin wire. The ends 47 and 47a of conductor 46 are substantially vertical and of substantially uniform cross section to minimize interference with vertical movement of the hydrometer.

It is desirable that conductor 46 be constructed of material which is highly resistant to chemical action. A conductor plated with noble metals, such as gold, exhibits the desired qualities.

The weight of conductor 46 must be taken into consideration when hydrometer 40 is calibrated because hydrometer 40 will sink deeper into the liquid with the conductor attached thereto than it would if the conductor were not attached. For example, to maintain the specific gravity of the solution in test chamber 4 at .970 the end 47 of conductor 46 must be set at .968 if the weight of the conductor varies the hydrometer reading .002.

It should be readily appreciated that no power is required to open and close the circuit between the solution 5 in test chamber 4 and the end 47 of the conductor 46. As hydrometer 40 moves upwardly as the specific gravity of the fluid increases, the end 47 of the conductor moves upwardly relative to the surface of the liquid until the end of the thin wire is withdrawn therefrom, breaking the electrical circuit, thus deenergizing coil 56 of relay 58, causing switch 56a to be closed, thereby opening valve 16 allowing alcohol to be drawn through venturi 12 into the solution, reducing the specific gravity thereof. The effect of surface tension of the liquid on the wire is negligible.

It should be readily apparent to a person having ordinary skill in the art that if it is desired to maintain the specific gravity of the sample solution in test chamber 4 above a desired FIG., the control device hereinbefore described may be utilized with minor modification. A liquid having a specific gravity greater than that of the fluid flowing through the circulating system 8 may be placed in fluid supply source 18. The only other change required of the system is to cause switch 56a of relay 58 to close as the end 47 of conductor wire 46 engages the sample solution in test chamber 4 by spring biasing the switch 56a open. This may be accomplished by connecting line 74' to the normally open contact 56d instead of the normally closed contact 56c of relay 58. Such modification would be within the skill of a person having ordinary skill in the art and further description thereof is not deemed necessary.

As hereinbefore pointed out the above described control system is particularly adaptable for use as a control device for automatically maintaining a desired specific gravity of dampening fluid used in lithographic printing. The relationship of the control device to the circulating and refrigeration system of a lithographic printing press is illustrated in FIG. I of the drawing.

A dampening fluid tank or reservoir 101 is provided, having heat insulation 102 in the walls thereof. A quantity of dampening fluid 103 may be conventional type of dampening fluid, which usually consists of a mixture of chemical ingredients in water, or it may be water and other chemical ingredients mixed with alcohol, as it is used with the dampening device disclosed in U.S. Pat. No. 3,168,037 to Harold P. Dahlgren. The level of the dampening fluid 103 is maintained above the impeller 104 of the pump 105. The impeller 104 is rotated through a shaft 106a by an electric motor 106 mounted on the top of the reservoir 101. The impeller 104 picks up dampening fluid from the container 101 through the intake opening 105a in the lower wall of the pump housing.

The dampening fluid is forced through the discharge line 107 and is passed through a refrigerator unit 108 which has the usual compressor, condenser, receiver, filter and dryer, expansion valve and evaporator coils therein. Discharge line 107 is connected to a pipe 109 which passes adjacent to the evaporator coils of the refrigeration unit, and as the dampening fluid passes therethrough, it is cooled. The temperature of the refrigeration unit may be maintained by a suitable thermostat control (not shown).

A portion of the refrigerated dampening fluid is passed from the pipe 109 through a hand operated valve 111 and a supply line 110 to the dispenser pipe 118 which is disposed in the dampening fluid pan or fountain 115.

A branch line 112 communicates with the upper part of the reservoir 101 through a discharge nipple 114.

A return hose 126 is attached to the outlet drain nipple 125 through which dampening fluid may return from the pan 115 to the reservoir 101. The hose 126 communicates with a drain back pipe 128 in the reservoir 101 through a suitable nipple 127 passing through the upper wall of the reservoir 101. The drain back pipe 128 is connected in communication with a T-fitting 129.

A restrictor nozzle 130 is connected between an outlet from the discharge conduit 107 and the T-fitting 129. A venturi 132 is connected to an outlet of the T-fitting 129 opposite the restrictor nozzle 130. A venturi discharge line 133 is connected to the opposite end of the venturi 132 and terminates at the bottom of the reservoir 101.

Dampening fluid circulating through supply line 110 into pan 115 is exposed to the atmosphere and the alcohol evaporates therefrom, changing the chemical composition of the dampening fluid, which results in a reduction of the quality of printing.

A T-fitting 10a is positioned in supply line 110 or branch line 112 for directing a portion of the fluid flowing therethrough through conduit 10 to the control device as hereinbefore explained.

Outlet conduit 26, which communicates with overflow tube 22 in mixing chamber 2 of the control device, extends through a suitable nipple 27 passing through the upper wall of the reservoir 101.

In multicolor printing a separate dampening fluid circulating system is normally used for the dampening system of each printing station. Therefore a conventional electrical outlet socket 79 is connected through lines 79a and 79b to lines 76 and 74 to facilitate connecting a series of control devices to a single source of electricity. Lines 74 and 76 of a second control device (not shown) may be connected to outlet 79 of the first control device.

The operation and function of the device hereinbefore described is as follows:

A portion of the dampening fluid 103 flowing through circulating system 8 is diverted through conduit 10 into mixing chamber 2 in the body 1 of the control device. A portion of the dampening fluid flows into control chamber 4 through passage 6 and the specific gravity of the dampening fluid is automatically tested by hydrometer 40 having a conductor 46 on the upper end thereof.

If alcohol has evaporated from the dampening fluid causing the specific gravity of the dampening fluid to be too high, the end 47 of conductor 46 will be disposed above the surface of the sample solution 5 of dampening fluid in test chamber 4 causing the electrical circuit to be broken, thus deenergizing relay 58 causing switch 56a to close thereby opening valve 16, allowing dampening fluid to flow from fluid supply source 18 as the result of the vacuum lift created at the throat of venturi 12.

Alcohol is thus automatically added to the system as required and is thoroughly mixed with fluid already in the system before being tested and released into the system.

Although this device has been disclosed primarily for automatically mixing alcohol with dampening fluid for use in lithographic printing it will be understood that it is useable for mixing any two fluids of different specific gravity.

In certain applications it may be desirable to control specific gravity of a solution which is not a good conductor of electricity. If the solution in control chamber 4 is nonconductive a circuit will not be completed between electrodes 50 and 52 when conductor 46 engages the solution therein. The embodiment of the invention illustrated in FIG. VIII of the drawing is a modified form for controlling the specific gravity of a nonconductive solution.

Control chamber 4' is identical to control chamber 4 hereinbefore described except that electrode 50' is submerged in an electrically conductive liquid 5', which is separated from the solution in control chamber 4' by a container 5a constructed of a suitable material which is not electrically conductive. The surface of liquid 5' is maintained at the same level as the surface of the solution in control chamber 4' by balancing the weight of container 5a and liquid 5' with buoyant force exerted thereon by liquid in the control chamber. If the surface of the solution in control chamber 4' is maintained at a constant level container 5a may be secured to the wall of the control chamber in the same manner as isolated solution receptacle 42'.

From the foregoing it should be readily apparent that when line 66' is connected to transformer 64 and line 54' is connected to relay 58 as hereinbefore described with respect to the embodiment of the invention illustrated in FIG. I of the drawing, that a circuit is completed from contact 52' through conductive liquid 44', conductor 46', conductive liquid 5', contact 50', conductor 54' to the transformer 64 and relay 56 as the end 47' of conductor 46' engages the surface of liquid 5' in container 5a. The operation of the remainder of the system hereinbefore described with respect to the first embodiment remains unchanged.

From the foregoing it should be readily apparent that I have developed a device for controlling the specific gravity of a solution of two or more fluids having different specific gravities readily adaptable to systems in which it is desirable to maintain a constant specific gravity of a solution circulated therethrough in which one of the fluids is depleted from the solution.

Claims

I claim:

1. In apparatus for regulating the specific gravity of a solution of first and second liquids comprising: a control chamber; means for admitting a solution of first and second liquids into the control chamber; electrically actuated means for injecting the first liquid into the solution for mixing therewith; a receptacle in the control chamber; an electrically conductive liquid in the receptacle; electrical insulation means separating the receptacle from the chamber; a hydrometer freely floating in the solution in the control chamber; a first electrode submerged in the solution in the chamber; a second electrode submerged in the liquid in the receptacle; an electrical circuit connected between the electrodes; a source of electricity in the circuit; switch means for connecting the circuit to the electrically actuated means; and an electrical conductor mounted on the hydrometer, said conductor having ends arranged to contact the solution in the control chamber and the liquid in the receptacle respectively, the hydrometer being movable upwardly in the solution in response to increase in the specific gravity thereof to cause one of the ends to break contact with the liquid in which it is disposed to thereby actuate the switch means.

2. The combination called for in claim 1 wherein the means for admitting a solution of first and second liquids into the control chamber includes a mixing chamber with means therein to mix the first and second liquids before admitting the solution into the control chamber.

3. The combination called for in claim 1 wherein the means for admitting a solution of first and second liquids into the control chamber includes means for eliminating air bubbles therefrom.

4. The combination called for in claim 1 wherein the electrical conductor mounted on the hydrometer comprises a conductor having one end submerged in the liquid in the receptacle and having the other end secured to the hydrometer and arranged to contact the solution in the control chamber as the hydrometer moves vertically relative thereto.

5. The combination called for in claim 1 wherein the means for admitting a solution of the first and second liquids into the control chamber includes a circulating system for a lithographic offset press dampening device; and means for directing liquid from the circulating system through the control chamber and back into the circulating system.

6. The combination called for in claim 1 wherein the switch means connecting the electrical circuit to the electrically actuated means for injecting first liquid into the solution includes current responsive switching means constructed and arranged to connect the electrically actuated means for injecting first fluid into the solution to a source of electricity when the electrical conductor on the hydrometer disengages the solution in the control chamber.

7. The combination called for in claim 1 wherein the switch means for connecting the electrical circuit to the electrically actuated means for injecting a first liquid into the solution includes current responsive means constructed and arranged to disconnect the electrically actuated means for injecting first liquid into the solution from a source of electricity when the electrical conductor engages the solution in the control chamber.

8. In a control device for regulating the specific gravity of a liquid solution comprising, a mixing chamber; a control chamber; an inlet to the mixing chamber for admitting liquid solution thereto; an outlet to the mixing chamber for discharging liquid solution therefrom; means in the mixing chamber for agitating the solution as it passes from the inlet to the outlet; a passage between the mixing chamber and the control chamber; a control chamber outlet passage communicating with the inside of the control chamber above the first named passage; an insulated receptacle in the control chamber, said receptacle having an open upper end disposed above the control chamber outlet passage; electrically conductive liquid in the receptacle; an electrode in the receptacle; an electrode in the control chamber; a freely floating hydrometer in the control chamber; an electrical conductor mounted on the hydrometer constructed and arranged to engage both the solution in the control chamber and the liquid in the receptacle as the specific gravity of the solution decreases to a predetermined value; electrically actuated means for injecting a liquid having a different specific gravity from that of the solution in the control chamber into the mixing chamber; and electrical actuating means operably connected between the electrodes and the electrically actuated means to cause the said liquid to be injected into the solution when the conductor on the hydrometer moves out of contact with the surface of the solution in the control chamber as the specific gravity of the solution changes.

9. The combination called for in claim 8 wherein the means in the mixing chamber for agitating the solution includes an overflow tube having an open upper end and a lower end communicating with the outlet.

10. The combination called for in claim 9 wherein the mixing chamber has a curved inner wall and the inlet is positioned to cause fluid to flow into the mixing chamber substantially tangent to the curvature of the wall thereof.

11. In apparatus for maintaining the density of a solution of at least two liquids at a predetermined value comprising: a chamber; a solution of liquids in the chamber; electric current responsive means for adding a liquid to the solution; a first electrode submerged in the solution in the chamber; a receptacle; electricity conductible liquid in the receptacle; a second electrode submerged in the conductible liquid in the receptacle; means connected to the electrodes for energizing the current responsive means when an electrical circuit is completed between the first and second electrodes; a hydrometer freely floating in the solution; and a conductor having at least two free ends mounted on the hydrometer, one of the free ends being submerged in the conductible liquid and the other free end being positioned to move vertically with the hydrometer relative to the surface of the solution and contact or move out of contact with the solution depending upon the vertical position of the hydrometer in the solution.

12. The combination called for in claim 11 with the addition of means to vary the vertical relationship between at least one end of the conductor on the hydrometer and the hydrometer.

13. In a device for automatically controlling the specific gravity of a solution of a multiplicity of liquids; a housing including a mixing chamber and a control chamber; means for circulating the solution through the mixing chamber; means for admitting a portion of the solution to the control chamber; a free floating hydrometer in the solution in the control chamber; an electrically insulated liquid receptacle mounted on the wall of the control chamber having an open end extending above the level of the solution therein; an electrical conductive liquid in the receptacle; means for controlling the level of the liquid in the mixing chamber; means for controlling the level of the liquid in the control chamber; an electric conductor secured to the hydrometer having free ends extending into the solution in the control chamber and the liquid in the receptacle respectively, the free end in the solution being arranged to move out of or into contact with the solution as the hydrometer rises or falls in the solution; an electrode in the solution in the control chamber; an electrode in the liquid in the receptacle; an electric circuit attached between the electrodes; means for admitting a liquid of a different specific gravity from that of the solution into the mixing chamber, said means including a container for said liquid; a conduit between the container and the mixing chamber, and an electrically actuated valve in the conduit; and electrically actuated switch means in the electric circuit operably connected to the valve to control the opening and closing of said valve responsive to the closing or opening of the circuit by downward and upward movement of the hydrometer in the solution in the control chamber.

14. The combination called for in claim 13 wherein the means for circulating the solution through the mixing chamber includes, a conduit; a venturi in the conduit, and the conduit between the container and the mixing chamber communicates with the outlet to the venturi whereby fluid is drawn from the container into the mixing chamber by the drop in pressure in the venturi.

15. The combination called for in claim 14 wherein the container is located below the level of the solution in the mixing chamber.

16. In a device for automatically controlling the specific gravity of a solution of a plurality of fluids, at least one of which is a volatile fluid, comprising a solution container; a quantity of solution in the container; a free floating hydrometer in the solution; an insulated liquid receptacle in the container having an open upper end above the solution; an electrically conductive liquid in the receptacle; an electrical conductor carried by the hydrometer having contacts contacting the solution and the liquid, at least one of which is arranged to move out of contact with the liquid or solution in which it is disposed in response to the predetermined rise of the hydrometer in the solution; and means to admit additional volatile fluid to the container including a conduit for said fluid, a solenoid valve controlling flow through the conduit, and an electric circuit in which the solenoid valve is disposed, which electric circuit is also in series with the contacts so that the circuit is opened or closed depending upon whether the contact in the solution container is out or in contact with the solution.

17. In a device for controlling the specific gravity of a solution of first and second liquids, comprising: a mixing chamber; means for admitting the solution into the mixing chamber; actuated means for admitting first liquid into the mixing chamber to be mixed with the solution; means in the mixing chamber for agitating the solution and the said first liquid; means for removing bubbles of gas from the solution; means for determining the specific gravity of the solution mixed with the said first liquid; actuating means operably connected between the actuated means for admitting first liquid and the means for determining the specific gravity of the solution, said actuating means being constructed and arranged to maintain the specific gravity of the liquid within predetermined limits.

18. The combination called for in claim 17 wherein the actuated means comprises electric current operated valve means; and the actuating means comprises a hydrometer floating in the solution, switching means actuated by the hydrometer, and an electrical circuit between the switching means and the valve means.

19. In a device for automatically controlling the specific gravity of a solution of a plurality of liquid ingredients, the combination comprising a container for the solution; current responsive means for adding at least one of the liquid ingredients to the solution; an insulated receptacle adjacent to the container; conductive liquid in the receptacle; a first electrode submerged in the liquid in the receptacle; a hydrometer freely floating in the solution in the container; a conductor having at least two free ends secured to the hydrometer; one of the free ends being submerged in the liquid in the receptacle and the other end being movable into and out of contact with the solution in response to movement of the hydrometer; a second electrode secured relative to the container such that an electrical circuit is completed between the conductor and the second electrode when the specific gravity of the solution changes to a predetermined value; and means electrically connected to the first and second electrodes and the current responsive means for adding at least one of the liquid ingredients to cause the liquid ingredient to be added when an electrical circuit is broken between the second electrode and the conductor.