GB2210687A

GB2210687A - Determining soil pH

Info

Publication number: GB2210687A
Application number: GB8823503A
Authority: GB
Inventors: Dudley Roger Lester
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-10-07
Filing date: 1988-10-06
Publication date: 1989-06-14
Anticipated expiration: 2008-10-06
Also published as: GB2210687B; GB8823503D0; GB8723534D0

Abstract

A dry composition for indicating the pH value of a sample of soil comprises one or more pH indicators and a settling agent e.g. BaSO4. When the composition is mixed with a sample of soil and water there forms a coloured supernatent liquid above the surface of the settled soil with the colour of said liquid providing the indication of the pH value of the sample of soil, wherein the one or more pH indicators are present on the surface of particles present in the composition. A process for making composition, a method of use and a kit to determine the pH value of a sample are also disclosed.

Description

SOIL TESTER This invention relates to soil testers and particularly a composition which may be used to indicate the pH value of a sample of soil, a process of producing the said composition and a method of determining the pH value of a sample of soil.

There are several soil testers currently available on the market. One such soil tester, available in kit form, uses a liquid solution which when mixed with a sample of soil produces a coloured supernatant liquid. The colour of the supernatant liquid may then be compared with a pH colour chart to determine the pH value of the sample of soil.

Other kits currently being manufactured use a settling agent, commonly barium sulphate, which is mixed with a sample of soil and water. The settling agent is used primarily to speed up the settling of the soil from suspension in the water and since it is the pH value of the sample of soil which is being determined the settling agent must be approximately neutral pH value so as not to affect the final results. A supernatant liquid forms above the top of the settled soil and a small drop of the liquid is removed by a dip-rod. The drop of the supernatant liquid is then placed in a depression formed in a plastic strip provided. The depression is coated with a substance which reacts with the supernatant liquid and colours the liquid. The colour, as in the previous example may be compared against a pH colour chart to determine the pH value of the sample of soil.

Problems exist for both of the above-mentioned soil testers. With the first kit a solution is supplied and although use of the testing kit is quite simple, problems arise in safely packaging the liquid and as a result the kit is relatively expensive.

With the second kit the problems involved in the packaging of the solution have been avoided but use of the kit is "fiddley" and complicated.

With the second kit it was necessary to investigate what effect the use of tap water, which is known to often have pH values other than 7, would have on the determined soil pH value. Therefore samples of soil, covering most of the types which the gardener is likely to encounter, were collected. In total 17 samples were collected because some soils are less buffered than others and so are more susceptible to the pH value of the added water.

These samples were then tested for their pH value using an electronic reader coupled to an "Ingold" glass electrode, having first been mixed with one of three types of water. It was found that the effect of using tap water instead of neutral distilled water was very small, the highest variation in reading being 0.25 pH although most of the variations were well below this figure.

This variation was totally acceptable for the testing kit since the accuracy of the testing kit was only approximately 0.50pH which is all that is necessary for a garden testing kit of this kind.

These experiments covered the most likely range of tap water pH values from 6.2pH from a borehole supply through 7pH of distilled water up to 8.7pH and 8.9pH from a municipal water supply.

It would therefore be desirable to provide a soil tester which has a composition incorporating both the settling agent and the pH indicators in the form of a dry powder. The powder could then be simply mixed with a sample of the soil and tap water, since the tap water would have no appreciable effect on the final result, and the resultant coloured supernatant liquid compared with a colour chart of pH values.

Difficulties arose in the production of such a composition in that separate batches of the composition would produce different colour changes for the same pH value. After extensive research it was found that this was due to a number of factors in the production of the composition each of which could independantly cause the variation in colour change for set pH values. These factors included variable precipitation out of solution at one stage of the manufacturing process and imperfect mixing of the substances during the drying process.

The present invention seeks to provide therefore a dry composition for indicating the pH value of a sample of soil, which composition comprises one or more pH indicators and a settling agent, the composition being such that when the composition is mixed with a sample of soil and water there forms a coloured supernatent liquid above the surface of the settled soil with the colour of said liquid providing the indication of the pH value. of the sample of soil, wherein the one or more pH indicators are present on the surface of particles present in the composition.

Preferably the dry composition comprises equal parts of the settling agent and the non-soluble particulate diluent mixed with one or more pH indicators or the non-soluble particulate diluent is added to the dry composition to prevent the composition from forming lumps and so allow the dry composition to flow freely when poured.

In addition preferably the settling agent is barium sulphate and the non-soluble particulate diluent is either silica sand or fine particles of glass or plastics. The pH indicators are preferably a mixture of methyl red and bromothylmol blue or ethyl red and bromothylmol blue though methyl orange and phenol may also be added.

A further aspect of the invention provides a process for preparing a composition as hereinbefore described wherein the settling agent is mixed with a solution containing at least one pH indicator, the solution is then subjected to a drying process, and the resultant dry composition is ground to a powder.

Preferably either further settling agent is mixed with, the dry composition after grinding or the non-soluble particulate diluent is mixed with the pH indicator solution, the resultant solution is then subjected to a drying process and after drying the dry composition is mixed with a settling agent.

Alternatively, equal parts of the settling agent and the non-soluble particulate diluent are mixed with a solution containing at least one pH indicator, the resultant solution is the subjected to a drying process and after drying is ground to a fine powder.

Preferably the solution is a very concentrated solution of the pH indicators, the solvent being predominantly water with a small amount of alcohol and wherein the solution has a pH value of 6.5. to 7.5 prior to drying. Preferably also the temperature during the drying process is not allowed to exceed 650C.

Another aspect of the invention provides a method for testing the pH value of a sample of soil wherein a measured amount of the composition as claimed in any one of claims 1 to 5 is mixed with the sample of soil and water, the mixture is then allowed to settle and the colour of the supernatant liquid is compared with a pH colour chart to determine the pH value of the sample of soil.

Preferably the composition is added to a graduated tube and fills the tube to the lowest mark, a sample of the soil to be tested is then added to the tube and fills the tube to the next lowest mark, finally tap water is added to the tube and fills the tube to the top mark; a stopper is then placed in the end of the tube and the tube and contents shaken vigorously for approximately thirty seconds, the contents of the tube is then allowed to settle for two minutes, after two minutes the colour of the supernatent liquid is compared with a pH colour chart and the pH value of the sample of soil is determined.

A final aspect of the invention provides a kit for testing the pH value of a sample of soil which provides a composition as hereinbefore described and a pH colour chart.

A preferred embodiment of the kit also provide a transparent graduated tube with a stopper, the kit being provided as a blister pack on a card with the pH colour chart printed on the card with the graduated tube and stopper with another container holding the composition positioned on the card within the blister.

This invention will now be further described with reference to the following non-limiting drawings and examples: Where Figure 1 illustrates the graduated container and contents; Figure 2 is an upper perspective view of the kit; and Figure 3 is a lower perspective view of the kit Example 1 Stock solutions of the pH indicators were prepared as follows: 5g of methyl red was mixed with 450ml of alcohol and 300ml of water, the mixture was shaken well and the pH value brought upto 7. The solution was then left overnight and later filtered to produce the methyl red indicator.

2g of bromothylmol blue was dissolved in 60ml of alcohol and 60ml of water. The mixture was shaken vigorously until completely dissolved. The solution was then diluted with water to a total of 360ml. 0.1N of sodium hydroxide was added until the colour of the solution turned light purple and the pH value became 6.9 to produce the methyl red indicator.

The above-mentioned stock solutions were then mixed with barium sulphate, technical grade, in the following amounts: Methyl red solution 70ml Bromothylmol blue solution 60ml Barium sulphate 220ml The resultant solution had a consistency of thin cream thus minimising the amount of water to be driven off in the drying process. It had been found that variable amounts of precipitation had occured in solution resulting in variable colour changes to set pH values and this was traced to the amount of alcohol present in the solvents. The solvents were therefore prepared containing predominantly water with only a small amount of alcohol included.

Barium sulphate was chosen since it has the necessary properties of producing rapid settling from a suspension and having a pH value of near neutral, so that the pH value of the barium sulphate would not interfere with the final pH value readings.

The resultant solution was dried at temperatures not exceeding 650C so as to ensure that there were consistent colour changes for set pH values. The resultant dried composition was then ground to a fine powder and finally to the powder a further 430ml of barium sulphate was added.

The resultant composition was then used to test a sample of soil. A small quantity of the composition (1) was added to a transparent container (2) with three marks (3) at differing heights along its side, the composition filling the container to the lowest mark. The soil to be tested (4) was added on top of the composition, filing the container up to the second mark; this used approximately 1g of the composition. Finally, ordinary tap water (5) was added to the container as far as the uppermost mark so that when the soil had settled there was a supernatent layer of liquid above the top of the soil. Once the water had been added, the mixture was shaken vigorously for 30 seconds and then left to stand for 2 minutes. After the 2 minutes the colour of the supernatent liquid was compared with a pH colour chart and the pH of the soil determined.The composition was capable of determining pH values from 4.5 to 7.5 with an accuracy of approximately 0.5 pH.

ExamPle 2 The stock solutions were made up as hereinbefore described, they were then mixed with barium sulphate and silica sand in the following quantities.

Methyl red solution 70ml Bromothylmol blue solution 60ml Barium sulphate 350ml Silica sand 350ml The resultant solution was then dried at a temperature not exceeding 650C and the dried composition was then ground to a fine powder. The sample of soil was then tested using the composition described above. The test used was the test as described in Example 1. By using silica sand not only does this limit the amount of grinding required since silica sand does not form lumps on drying but also the silica sand acts as an aid to easy pouring of the resultant dried composition. The barium sulphate has a tendency to form lumps and so is difficult to pour out accurately. By adding silica sand the composition remains lump free and so is easier to pour, by making the composition more free flowing, and measure.

Similar compositions were prepared using the following quantities: a) Methyl red solution 70ml Bromothylmol blue solution 60ml Barium sulphate 220ml Once mixed, the resultant solution was dried at a temperature not exceeding 65 C and ground. Once ground a further 430ml of barium sulphate was added.

b) Methyl red solution 70ml Bromothylmol blue solution 60ml Silica sand 500ml Once mixed, the resultant solution was dried at a temperature not exceeding 650C to its granular state. Once dried, 300ml of barium sulphate was added and mixed with the dried composition. Instead of silica sand any other non-soluable particulate material may be used for example fine particles of glass or plastics so as to improve the flow characteristics of the dry composition.

c) Methyl red solution 100ml Methyl orange solution 35ml Bromothylmol blue solution 30ml Water 285ml Barium sulphate 1300g Once mixed, the resultant solution was dried at a temperature not exceeding 650C and once dried was then ground to a fine powder.

The methyl orange stock solution was prepared by dissolving lg of methyl orange in 300ml of hot water. The mixture was allowed to cool and then had the pH valuve brought to 6.9. 50ml of alcohol was then added to the mixture and the mixture was shaken and filtered.

A similar composition was prepared but using the following pH indicators: ethyl red, methyl orange and bromothylmol blue in the same quantities. Also phenol red indicator was added in small quantities.

The resultant composition when used to indicate the pH value of a sample of soil produced particularly sharp colour changes between different pH values.

Owing to the addition of the phenol red indicator the composition had an extended indicating alkaline range of pH values of 9 or 10.

Example 3 A testing kit was prepared for use in determining the pH values of soil samples incorporating a composition as hereinbefore described. The kit (6) was made as a blister pack (9) on a card (7), the card having a hole (8) near to the top edge so that it could be displayed collectively on a peg in a shop. The card of approximately 190mm x 102mm had the instructions for use and a pH colour chart printed on the front and plant pH preferences printed on the back. Within the blister pack (9) two containers were supplied, one was a transparent container (10) with graduated markings up the side and a stopper, the other container (11) held the composition as hereinbefore described.

The container held approximately 10g of the powder which was sufficient for 10 tests.

Further testing kits in accordance with the invention provide a measuring spoon instead of a graduated container and the composition in sachets or capsule form.

Claims

CLAIMS:

1. A dry composition for indicating the pH value of a sample of soil, which composition comprises one or more pH indicators and a settling agent, the composition being such that when the composition is mixed with a sample of soil and water there forms a coloured supernatent liquid above the surface of the settled soil with the colour of said liquid providing the indication of the pH value of the sample of soil, wherein the one or more pH indicators are present on the surface of particles present in the composition.

2. A dry composition as claimed in Claim 1, wherein equal parts of the settling agent and the non-soluble particulate diluent are mixed with one or more pH indicators to form the said dry composition.

3. A dry composition as claimed in Claim 1, wherein a non-soluble particulate diluent is added to the dry composition to prevent the composition from forming lumps and so allow the dry composition to flow freely when poured.

4. A dry composition as claimed in any of Claims 1 to 3, wherein the settling agent is barium sulphate.

5. A dry composition as claimed in any of Claims to 4, wherein the non-soluble particulate diluent is silica sand.

6. A dry composition as claimed in any of Claims to 4, wherein the non-soluble particulate diluent is fine particles of glass or plastics.

7. A dry composition as claimed in any of Claims 1 to 6, wherein the pH indicators are a mixture of methyl red and bromothymol blue, said mixture being capable of indicating a range of pH values between 4.5 and 7.5.

8. A dry composition as claimed in Claim 7, wherein methyl orange is added to the mixture of methyl red and bromothymol blue pH indicators.

9. A dry composition as claimed in Claims 1 to 6, wherein the pH indicators are a mixture of ethyl red and bromothymol blue.

10. A dry composition as claimed in Claim 9, wherein methyl orange is added to the mixture of ethyl red and bromothymol blue pH indicators.

11. A dry composition as claimed in any of Claims 7 to 10, wherein a small quantity of phenol red pH indicator is added to achieve an extended alkaline indicator range up to pH values of 9 or 10.

12. A process for preparing a dry composition as claimed in Claim 1, wherein- the settling agent is mixed with a solution containing at least one pH indicator, the solution is then subjected to a drying process, and the resultant dry composition is ground to a powder.

13. A process as claimed in Claim 12, wherein further settling agent is mixed with the dry composition after grinding.

14. A process for preparing a dry composition as claimed in Claim 1, wherein the non-soluble, particulate diluent is mixed with a solution containing at least one pH indicator, the resultant solution is then subjected to a drying process and after drying the dry composition is mixed with a settling agent.

15. A process for preparing a dry composition as claimed in Claim 2, wherein equal parts of the settling agent and the non-soluble particulate diluent are mixed with a solution containing at least one pH indicator, the resultant solution is then subjected to a drying process and after drying is ground to a fine powder.

16. A process as claimed in Claim 3, wherein the non-soluble particulate diluent is mixed with the dry composition after drying.

17. A process as claimed in any of Claims 12 to 16, wherein the solution is a very concentrated solution of the pH indicators, the solvent being predominantly water and a small amount of alcohol.

18. A process as claimed in any of Claims 12 to 17, wherein the solution has a pH value of 6.5 to 7.5 prior to drying.

19. A process as claimed in any of Claims 12 to 18, wherein the temperature during the drying process is not allowed to exceed 650C.

20. A composition when produced by the processes claimed in any of Claims 12 to 19.

21. A method for testing the pH value of a sample of soil, wherein a measured amount of the composition as claimed in any of Claims 1 to 11 and 20 is mixed with the sample of soil and water, the mixture is then allowed to settle and the colour of the supernatent liquid is compared with a pH colour chart to determine the pH value of the sample of soil.

22. A method as claimed in claim 21, wherein the composition is added to a graduated tube and fills the tube to the lowest mark, a sample of the soil to be tested is then added to the tube and fills the tube to the second lowest mark, finally tap water is added to the tube and fills the tube to the top mark; a stopper is then placed in the end of the tube and the tube and contents shaken vigorously for approximately thirty seconds, the contents of the tube is then allowed to settle for two minutes, after two. minutes the colour of the supernatant liquid is compared with a pH colour chart and the pH value of the sample of soil is determined.

23. A kit for testing the pH value of a sample of soil which provides a composition as claimed in any of Claims 1 to 11 and 20 and a pH colour chart.

24. A kit as claimed in Claim 23 further providing a transparent graduated tube with a stopper, the kit being provided as a blister pack on a card with the pH colour chart printed on the card with the graduated tube and stopper with another container holding the composition positioned on the card within the blister.

25. A composition as claimed in any of Claims 1 to 11 and 20 substantially as hereinbefore described with reference to any one of the examples.

26. A process as claimed in any of Claims 12 to 19 substantially as hereinbefore described with reference to and as shown in any one of the drawings or examples.

27. A method as claimed in either of Claims 21 or 22 substantially as hereinbefore described with reference to any one of the examples.

28. A kit as claimed in Claim 23 substantially as hereinbefore described with reference to and as shown in any one of the drawings.