JP2005245964A - Disinfectant solution filling container - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an easy-to-carry container to be filled with an aqueous solution of a microbicide in which an aqueous solution of a weakly acidic hypochlorous acid with a strong microbicidal power can be stored in the condition where effective chlorine concentration is stably kept. <P>SOLUTION: The aqueous solution of the weakly acidic hypochlorous acid in which the effective chlorine concentration is adjusted to be in the range of pH of 3-6.5 by using carbon dioxide or the like to an alkaline sodium hypochlorite aqueous solution with an effective chlorine concentration of 1-2,000 ppm, is filled in a container made from an aluminum metal or an aluminum metal with an oxidatively treated surface. When using an aerosol can as the container to be filled with the solution, the aerosol can filled with the aqueous solution of the weakly acidic hypochlorous acid is provided easily, by the use of carbon dioxide as a filling gas. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a portable bactericide aqueous solution filling container filled with a chlorine-based bactericide aqueous solution, and is applied to various industrial fields such as medical field and food field and general households.

  Chlorine disinfectants represented by sodium hypochlorite, depending on their effective chlorine concentration, can effectively disinfect or inactivate general bacteria such as E. coli, yeast-like, filamentous fungi, tuberculosis bacteria and viruses. Although widely used, its bactericidal power is due to the strong oxidizing action of hypochlorous acid (HClO).

  On the other hand, since hypochlorous acid is a weak acid, the alkaline sodium hypochlorite aqueous solution dissociates into hypochlorite ions (ClO-), so that the sterilizing power is 80 compared with the state of hypochlorous acid. It is said to decrease to 1/100. For this purpose, a method in which an aqueous solution of sodium hypochlorite is ion-exchanged with a hydrogen-type ion exchange resin to obtain hypochlorous acid, or an acidic substance is dissolved in an aqueous solution of sodium hypochlorite to bring PH to a range of 3 to 6. Have been proposed (see Patent Document 1). Furthermore, a method for producing weakly acidic chlorinated sterilized water by bubbling carbon dioxide in an aqueous sodium hypochlorite solution has also been proposed (see Patent Document 2).

Now, hypochlorous acid has poor storage stability, and has a drawback that its effective chlorine is reduced by light and heat. For this reason, it has been difficult to pack and transport in a small container. In order to solve these disadvantages, plastic containers are filled with stable electrolyzed water such as salt water, and the electrolyzer is installed in the spray device. The salt water is electrolyzed during spraying and sprayed as hypochlorous acid. Recently, a portable device has been proposed (see Patent Document 3). In addition, an aerosol can type bactericide storage can was proposed in which hypochlorous acid was filled using a filling gas in a container in which the inner wall of a pressure-resistant metal can excellent in hermeticity and light shielding properties was coated with fluororesin. (See Patent Document 4).
JP-A-10-182325 (2nd page, FIG. 3) JP 10-24294 A (page 2) Japanese Patent Laying-Open No. 2003-181338 (second page, FIG. 1) JP 2003-34375 A (page 2)

  The present inventor has confirmed that when PH is weakly acidic by adding an acid to sodium hypochlorite exhibiting alkalinity as disclosed in the prior art, the sterilizing power is very excellent. Further, it was confirmed that the pH of the chlorine-based disinfectant can be made weakly acidic by using carbon dioxide as the acid to be added. Therefore, it was an object to develop a portable product with excellent storage stability filled with this chlorine-based disinfectant.

  The inventor has focused on an aerosol can type container in which cosmetics, hairdressing agents, and the like are pressurized and filled with a compressible gas as an easily transportable container having excellent storage stability. In general, such an aerosol can container is often made of aluminum metal because of its light weight, and the inner wall of the can is coated with a phenolic resin or the like in order to prevent corrosion of the aluminum metal. The present inventor has found that such an aluminum can is filled with a chlorine-based disinfectant aqueous solution and the change in the effective chlorine concentration is examined, and the concentration decreases in a short time. However, when a hypochlorous acid aqueous solution adjusted to weak acidity is brought into contact with metallic aluminum without a coating resin, it is surprisingly found that the effective chlorine concentration does not decrease over a long period of time and there is no corrosion of metallic aluminum. Thus, the present invention has been completed.

  In other words, in the present invention, a chlorine-based disinfectant aqueous solution having a PH in the range of 3 to 6.5 and an effective chlorine concentration in the range of 1 ppm to 2000 ppm is filled in a metal aluminum or metal aluminum container whose surface is oxidized. This is a container filled with an aqueous bactericide solution. Furthermore, it is preferable that this aqueous chlorine-based disinfectant is an aerosol can that is pressurized and filled in the container with at least one gas selected from carbon dioxide, compressible gas, and liquefied gas. Moreover, it is preferable that the chlorine-based disinfectant aqueous solution is composed of hypochlorous acid, and it is preferable that the pH is adjusted only with carbon dioxide gas. The present invention is described in further detail below.

  The chlorine-based disinfectant aqueous solution of the present invention is an aqueous solution of hypochlorite such as sodium hypochlorite, potassium hypochlorite, calcium hypochlorite (bleaching powder), dichloromethane such as sodium dichloroisocyanurate, potassium, etc. An aqueous solution of isocyanurate is exemplified, and sodium hypochlorite is particularly preferable from the viewpoint of cost and bactericidal activity. Therefore, the following description will focus on the sodium hypochlorite aqueous solution. Since the aqueous sodium hypochlorite solution is alkaline, although PH changes depending on the effective chlorine concentration, when this aqueous solution is brought into contact with metallic aluminum, the hydrolysis of aluminum proceeds to produce aluminum hydroxide. Therefore, it is not possible to fill a metal aluminum container with an aqueous alkaline disinfectant solution such as sodium hypochlorite.

  On the other hand, aluminum aerosol cans filled with cosmetics and hairdressing agents are generally coated on the inner wall of the aluminum can with a phenolic resin or the like in order to prevent corrosion of the aluminum can from the contents. The present inventor adds carbon dioxide gas to an aqueous sodium hypochlorite solution to increase the sterilizing power, adjusts its pH to a weakly acidic range of 3 to 6.5, and fills a commercially available resin-coated aluminum can. Then, the corrosion state of the can and the change of the effective chlorine concentration were investigated. As a result, the corrosion of the can did not occur, but the effective chlorine concentration decreased in a short time (see Comparative Examples 1 and 2).

  In order to elucidate the cause, the aluminum plate coated with the above resin coat was disassembled to reveal the cause, and the aluminum plate with the resin coat adhered to the surface and the aluminum plate with the resin coat removed with a paper file to expose the aluminum base metal Were prepared and immersed in a weakly acidic hypochlorous acid aqueous solution containing 20 ppm and 200 ppm of effective chlorine concentration, and the change in corrosion state and effective chlorine concentration was examined. As a result, I found a surprising fact. That is, in the case of a resin-coated aluminum plate, the concentration decreases in a short time regardless of the effective chlorine concentration, but in the case of an aluminum metal, the effective chlorine concentration decreases in a short time when the concentration is 20 ppm. However, in the case of 200 ppm, it was found that it does not decrease and exists stably for a long time (see Reference Example 1). Further, corrosion of the aluminum ingot did not occur at all at 20 ppm or 200 ppm.

  In order to further investigate this phenomenon, a metal aluminum foil was used as a model of the aluminum bullion, and it was immersed in weakly acidic hypochlorous acid aqueous solutions with various effective chlorine concentrations to change the corrosion degree of the aluminum foil and the changes in the effective chlorine concentration. Tracked. As a result, it was found that when the initial effective chlorine concentration was about 60 ppm or more, the concentration did not change (see Reference Example 2).

  Considering this phenomenon, weakly acidic hypochlorous acid having a pH of 3 to 6.5 is a state of HOCl in which 90% or more is not dissociated as understood from the dissociation curve. In this state, strong oxidizing power is exhibited. Show. Therefore, it is considered that when weakly acidic hypochlorous acid is brought into contact with aluminum metal, the surface of the aluminum metal is oxidized and an oxide film is formed to prevent corrosion of the aluminum metal. When the initial effective chlorine concentration is as low as 20 ppm, for example, the oxidizing power of hypochlorous acid is relatively weak, so hypochlorous acid is consumed to form an oxide film, and the effective chlorine is completely consumed in a short time. . On the other hand, when the effective chlorine concentration at the initial stage is 60 ppm or more, hypochlorous acid is strongly consumed and the hypochlorous acid is hardly consumed for forming the oxide film, and the effective chlorine concentration can be maintained for a long time. It is considered a thing.

  The effective chlorine concentration of the weakly acidic hypochlorous acid aqueous solution in contact with the aluminum ingot does not change with time. If the initial effective chlorine concentration is about 60 ppm or more, there is no upper limit, but if it is too high, carbon dioxide etc. Therefore, the pH is preferably 2000 ppm or less and 1000 ppm or less because it is difficult to make PH a weak acidity of 6.5 or less and there is a risk other than metal corrosion.

  In order to further confirm the above-described consideration of the formation of the oxide film on the surface of the metal aluminum, an experiment similar to the above was performed using a material in which the surface of the metal aluminum was previously formed by anodizing (see Reference Example 3). ). As a result, in this case, since the oxide film is formed on the aluminum metal surface from the beginning, even when the effective chlorine concentration of the initial weakly acidic hypochlorous acid is as low as 20 ppm, the effective chlorine concentration does not change with time and is stable. Hypochlorous acid was found to be present. In addition, surface corrosion did not occur as expected. The alumite treatment of the aluminum metal can be performed by a known method.

  Therefore, when using a container made of aluminum metal, the effective chlorine concentration of the weakly acidic chlorine-based disinfectant aqueous solution to be filled needs to be 60 ppm or more, but when using an aluminum container whose surface is oxidized by alumite treatment or the like, There is no lower limit of the concentration, and 1 ppm or more is preferable from the viewpoint of bactericidal efficacy.

The pH of the weakly acidic hypochlorous acid aqueous solution of the present invention is not preferable because the pH becomes 3 or less as shown in the dissociation curve because chlorine gas is generated, and when the pH is 6.5 or more, it is not preferable. Therefore, it is not preferable in terms of sterilizing power. Therefore, PH needs to be adjusted to a range of 3 to 6.5. Further, since the PH that is present 100% without dissociating hypochlorous acid is in the range of 4 to 5.5, it is more preferable to adjust the PH to this range. In order to adjust the acidity within this range, an acid may be added to an alkaline aqueous sodium hypochlorite solution. The conditions required for the acid that can be used in the present invention are as follows: 1) Even when added to an aqueous sodium hypochlorite solution, the effective chlorine is not consumed.
2) Even if the hypochlorous acid aqueous solution adjusted to weak acidity by adding acid is brought into contact with metal aluminum or anodized aluminum, the effective chlorine is not consumed.
These two points are necessary.

As a result of experiments on various acids, organic acids such as tartaric acid and citric acid cannot satisfy the condition of 1), and PH decreases to 6.5 or less, but effective chlorine is consumed. It was found that acetic acid satisfies the condition 1) but does not satisfy the condition 2) (see Reference Example 4). Some inorganic acids do not satisfy these two conditions, so care must be taken when selecting an acid for adjusting the pH. As a result of examining various acids, it was found that inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid and carbon dioxide are effective acids that satisfy the conditions of 1) and 2).

  In particular, carbon dioxide is weakly acidic when dissolved in water, and its acid strength is a stronger acid than hypochlorous acid. That is, even if excess carbon dioxide gas is added to the sodium hypochlorite aqueous solution, the carbonic acid is weakly acidic, so that the pH is easily adjusted to the range of 3 to 6.5 without lowering the pH to 3 or less. Can do. On the other hand, if a strong acid such as hydrochloric acid is added in a slightly excessive amount, the pH becomes 3 or less, and generation of chlorine occurs. Carbon dioxide gas may be added to the sodium hypochlorite aqueous solution under pressure by directly injecting carbon dioxide gas into the aqueous solution from a gas cylinder. In some cases, water (carbonated water) in which carbon dioxide gas is dissolved is added to the sodium hypochlorite aqueous solution. May be mixed with.

  When using an aluminum aerosol can, it is preferable that the aqueous sodium hypochlorite solution is directly adjusted to weak acid with an acid before filling the aerosol can with a filling gas in order to avoid direct contact with aluminum. . In the case of anodized aerosol cans, corrosion does not occur even in an alkaline sodium hypochlorite aqueous solution for a short time (the alumite surface changes to pink when it is in contact for a long time, and corrosion proceeds). It is also possible to adjust to weak acidity by pouring a sodium hypochlorite aqueous solution into the can and filling it with carbon dioxide as a filling gas.

  Carbon dioxide is preferred as the filling gas for aerosol cans, but carbon dioxide has a high solubility in aqueous solution, so if the amount of residual liquid in the aerosol cans decreases, the internal pressure may decrease and the jetting power of the liquid may decrease. . In such a case, a gas having low solubility in water, for example, a compressible gas such as nitrogen gas, oxygen gas, argon gas, air, or helium can be used. Also, liquefied gas such as liquefied petroleum gas (LPG), liquefied natural gas (LNG), propane, butane, isobutane, dimethyl ether, etc. can be used alone or as a mixture as a gas having a strong injection force. Accordingly, it is preferable to use one or more of carbon dioxide gas, the compressible gas, and the liquefied gas as the filling gas.

  In the case of an aerosol can, a valve with a spray nozzle is attached to the lid of the can body, and examples of components used in these can include aluminum, plastic tubes, rubber packing, metal springs, etc. It is necessary to use a material that does not corrode or deteriorate with weakly acidic hypochlorous acid. It is also necessary that the effective chlorine concentration is not consumed in contact with these materials.

  As can be seen from the above explanation, the container filled with the aqueous chlorine-based disinfectant of the present invention can directly use a container made of metal aluminum or surface-oxidized aluminum. Therefore, these metal surfaces may be protected with a plastic that does not deteriorate with weakly acidic hypochlorous acid and does not consume the effective chlorine. Examples of these plastics include polyethylene, polyester, polyvinyl chloride, and fluororesin. As a protection method, these resins may be coated on the surface of an aluminum metal, or a bag is separately formed with a film made of these resins, and the bag is inserted into an aluminum can to disinfect a bactericidal solution. The bag may be filled.

  Although the above explanation has been given of the case where sodium hypochlorite is used as the hypochlorite, the same applies to the case where bleaching powder which is a calcium salt is used. In the case of bleaching powder, advanced bleaching powder with an effective chlorine concentration of about 60% is commercially available, but this is dissolved in water so that it has a predetermined effective chlorine concentration, and carbon dioxide or acid is added to achieve a predetermined weak acidity. It can be adjusted to PH.

  On the other hand, a solid sodium salt is generally used for dichloroisocyanurate, and this also has a commercially available effective chlorine concentration of about 60%. When this is dissolved in water, the pH of the aqueous solution is close to that of hypochlorite, and when an aqueous solution having an effective chlorine concentration of 1 ppm to 2000 ppm is prepared, the pH changes between 6.3 and 6.5. . In this PH range, chlorine can be present in a state of 90% or more of hypochlorous acid, but it is preferable to adjust the pH to a range of 4 to 5.5 in order to keep the state of near 100%. Therefore, as explained in the sodium hypochlorite aqueous solution, carbon dioxide gas or acid is added to adjust the pH to the range of 4 to 5.5, and it is filled in an aerosol can made of aluminum metal or anodized aluminum, or PH It is also possible to fill the container with the aqueous solution before adjustment directly using carbon dioxide as a filling gas.

  In addition to the above, the method of adjusting the weakly acidic hypochlorous acid aqueous solution can be adjusted by electrolyzing a chloride aqueous solution such as sodium chloride. In that case, the aqueous solution to be electrolyzed may be adjusted in advance to be electrolyzed, or may be adjusted to be weakly acidic by adding an acid to the aqueous solution after electrolysis. As the acid used at this time, the above-mentioned acids can be used, but carbon dioxide is preferred and a pH adjusting agent.

  Hereinafter, the present invention will be described in more detail with reference to Comparative Examples and Reference Examples. In addition, the measurement of the effective chlorine concentration used in the following examples employs an analysis method using a standard colorimetric plate using Organoquick (a simple water quality test kit manufactured by Organo, a colorimetric method using an O-toluidine indicator). . However, since the measurement concentration range was from 0.1 ppm to 5 ppm, the high concentration aqueous solution was appropriately diluted with ion-exchanged water (abbreviated as DI water) and measured.

Comparative Example 1
A commercially available sodium hypochlorite aqueous solution (effective chlorine concentration 12%) was diluted with DI water to prepare an aqueous solution having an effective chlorine concentration of 20 ppm (PH = 9.1) and 200 ppm (PH = 10.5). The inner pressure of the aerosol can is set to 0 using carbon dioxide as a filling gas using an aluminum aerosol can (150 ml in volume) coated with a commercially available epoxy phenol resin on the inner wall and an aluminum valve coated with the same resin as the can body. 100 ml of the above-mentioned sodium hypochlorite aqueous solution was filled so as to be 7 MPa.

This aerosol can (A: 20 ppm, B: 200 ppm) was stored at room temperature, and after one month, a bactericidal solution was sprayed from each container into a beaker, and its PH and effective chlorine concentration were measured. The PH values of aerosol cans A and B were 4.54 and 5.35, which were weakly acidic, but the effective chlorine concentrations were both reduced to 0.1 ppm or less. The aluminum can was disassembled and examined for corrosion, but no corrosion occurred.

Comparative Example 2

In the same manner as in Comparative Example 1, an aerosol can was filled with a sodium hypochlorite aqueous solution having an effective chlorine concentration of 20 ppm (A) and 200 ppm (B). In this example, a polyethylene bag was mounted inside the aluminum can body, and the bag was filled with an aqueous solution of sodium hypochlorite, and sealed with the same valve used in Comparative Example 1. The aerosol can was filled and stored at room temperature, and after 1 month, the PH and effective chlorine concentration of the contents were measured in the same manner as in Comparative Example 1. As a result, PH was 4.44 for A and 5.30 for B, which was slightly acidic, but the effective chlorine concentration was reduced to 0.1 ppm for A and 30 ppm for B.

Reference Example 1

The aluminum aerosol can used in Comparative Example 2 was disassembled, and an aluminum sheet metal (A) having an epoxy phenol resin coated on one side corresponding to the inner wall of the can was cut out. In addition, an aluminum plate (B) in which the resin was removed by rubbing with a paper file to expose the aluminum ingot was also prepared. In the same manner as in Comparative Example 1, an aqueous sodium hypochlorite solution having an effective chlorine concentration of 20 ppm and 200 ppm was prepared. The aqueous solution was placed in a PET bottle with the upper space left, and stirred with a magnetic stirrer. The upper space of the PET bottle and a carbon dioxide gas cylinder were connected by a tube, and 0.2 MPa gas was supplied for 1 hour to dissolve the carbon dioxide under pressure.

As a result, a weakly acidic hypochlorous acid aqueous solution having pH of 4.16 (20 ppm solution) and 5.09 (200 ppm solution) was prepared, respectively, and the aluminum plates A and B prepared above were immersed in this aqueous solution at room temperature. It was preserved and the change over time in its effective chlorine concentration was examined. The results are shown in Table 1. In either case, corrosion of the aluminum plate was not observed.

Reference Example 2
In the same manner as in Reference Example 1, weakly acidic hypochlorous acid having an effective chlorine concentration of 200 ppm (PH = 5.15) was prepared. Further, DI water was put into a PET bottle, and carbonated water (PH = 3.80) in which carbon dioxide gas was dissolved was prepared in the same manner as in Reference Example 1. The 200 ppm weakly acidic hypochlorous acid aqueous solution and this carbonated water were mixed to obtain 20 (PH = 4.22), 50 (PH = 4.76), 60 (PH = 4.79), 80 ppm (PH = 4 .97) A weakly acidic hypochlorous acid aqueous solution having an effective chlorine concentration was prepared. Aluminum foil was immersed in these aqueous solutions and stored at room temperature, and changes in the effective chlorine concentration were examined. The results are summarized in Table 2. In any case, the aluminum foil showed a metallic luster and no corrosion was observed.

Reference Example 3
Anodized with an aluminum bar. Using this rod, Reference Example 2. The sample was immersed in an aqueous solution of weakly acidic hypochlorous acid and effective chlorine concentrations of 20 ppm and 200 ppm prepared in step 1 and stored at room temperature for 1 month, and changes in the effective chlorine concentration were examined. As a result, unlike the case of aluminum metal, no change in the effective chlorine concentration was observed in either case of 20 ppm or 200 ppm. In addition, the alumite surface maintained a metallic luster and no corrosion occurred.

Reference Example 4
A commercially available sodium hypochlorite aqueous solution (effective chlorine concentration 12%) was diluted with DI water to prepare an aqueous solution having an effective chlorine concentration of 20, 200 ppm. To this aqueous solution, hydrochloric acid, sodium dihydrogen phosphate, and acetic anhydride were added as acids to prepare a weakly acidic hypochlorous acid aqueous solution. An aluminum foil was immersed in this aqueous solution in the same manner as in Reference Example 2 and stored at room temperature, and the change over time in the effective chlorine concentration was examined. The results are summarized in Table 3.

  By using the present invention, a metal aluminum or anodized aluminum container can be easily manufactured, for example, an aerosol can, which is stably filled with hypochlorous acid having strong sterilizing power. Moreover, when the bactericidal agent of the present invention when only carbon dioxide is used as a pH adjusting agent is applied to a contaminant, a clean bactericidal agent can be provided with almost no residue from the bactericidal agent. Since these aerosol cans are easy to carry, they can be sprayed and used in the required amount when necessary, so that hygiene management of a place where sterilization is required is achieved.

  The best mode for carrying out the invention will be described with reference to the following examples.

  An aerosol can made of aluminum metal having a volume of 200 ml not coated with resin and a valve (no aluminum resin coating) were prepared. On the other hand, a commercially available aqueous sodium hypochlorite solution (effective chlorine concentration 12%) was diluted with DI water to prepare an aqueous solution having an effective chlorine concentration of 200 ppm. Using this aqueous solution, a carbon dioxide gas was dissolved under pressure in the same manner as in Reference Example 1 to prepare a weakly acidic hypochlorous acid aqueous solution. Further, this aqueous solution was diluted 2.5 times with carbonated water in the same manner as in Reference Example 2 to prepare a weakly acidic hypochlorous acid aqueous solution having an effective chlorine concentration of 80 ppm. The pH values of 200 ppm (A) and 80 ppm (B) were 5.10 and 4.95, respectively.

150 ml of this aqueous solution was filled into the aerosol can prepared above with nitrogen gas as a filling gas at an internal pressure of 1.0 MPa. This aerosol can was stored at room temperature for 1 month, and the pH and effective chlorine concentration of the spray solution were measured in the same manner as in Comparative Example 1. As a result, the aerosol cans A and B had PH of 5.15 and 5.00, and the effective chlorine concentrations were 200 and 80 ppm, respectively.

  An aerosol can made of aluminum metal having a volume of 200 ml subjected to alumite treatment and a valve were prepared. In the same manner as in Example 1, an aqueous sodium hypochlorite solution having an effective chlorine concentration of 200 ppm was prepared. This aqueous solution was further diluted 10 times with DI water to prepare an aqueous sodium hypochlorite solution having an effective chlorine concentration of 20 ppm. Each PH was 10.29 for the 200 ppm solution and 8.40 for the 20 ppm solution.

  This aqueous solution was filled in the above cans with carbon dioxide as a filling gas so that the internal pressure was 0.8 MPa, and a valve was attached to make an aerosol can. After storing this aerosol can at room temperature for 1 month, the spray solution was received in a beaker and its pH and effective chlorine concentration were measured. As a result, there was no change in the effective chlorine concentration, and the PH values were 4.18 (20 ppm solution) and 5.17 (200 ppm solution), respectively.

  A container filled with a weakly acidic hypochlorous acid-filled aqueous chlorine-based disinfectant solution produced in the present invention is excellent in bactericidal power and easy to carry. Therefore, medical-related industries, food-related industries, and public health management Widely used in required dining halls, baths, toilets, etc.

Claims (4)

  A chlorine-based disinfectant aqueous solution having a PH in the range of 3 to 6.5 and an effective chlorine concentration in the range of 1 ppm to 2000 ppm is filled in a metal aluminum or metal aluminum container whose surface is oxidized. A container filled with a bactericidal solution.   The filling container of claim 1, which is an aerosol can filled with pressure with at least one gas selected from carbon dioxide, compressible gas, and liquefied gas. The sterilizing agent aqueous solution filling container according to claim 1 or 2, wherein the chlorinated sterilizing agent aqueous solution is composed of hypochlorous acid. The container for filling an aqueous bactericide solution according to claim 1 or 2, wherein the pH is adjusted only with carbon dioxide gas.