GB2177508A

GB2177508A - Testing of soil

Info

Publication number: GB2177508A
Application number: GB08616044A
Authority: GB
Inventors: Dudley Roger Lester
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-07-01
Filing date: 1986-07-01
Publication date: 1987-01-21
Also published as: GB8616044D0

Abstract

A soil testing element for inclusion in a kit comprises a strip of white synthetic plastics material having a depression in it. The depression is coated with a pH indicator. Water from above a settled soil suspension is transferred by means of a dip rod to the depression. Barium sulphate optionally mixed with a small amount of aluminium oxide may be added to a clay soil in preparing a suspension to be tested. A testing element may have two differently coated depressions. A coating may comprise a nitrogen-responsive colour change indicator. <IMAGE>

Description

SPECIFICATION Testing of soil This invention relates to the testing of soil.

According to a first aspect of the present invention there is provided a pH testing element which is of water impervious sheet material with a depression therein, the depression being coated with a pH indicator.

The element is preferably of elongate rectangular form with the depression near one end thereof and the other end forming a gripping portion.

In one specific form the testing element has two depressions therein, the depressions being coated with two different pH indicators.

According to a second aspect of the present invention there is provided a kit including a plurality of elements described above, and a colour chart printed with areas showing the colours taken-up by said pH indicator(s) in response to the application thereto of water of varying pH.

The kit can further include a rod which can be dipped into the water being tested so as to pick up a drop of water which can be placed in said depression(s).

According to a further aspect of the present invention there is provided a sheet comprising a plurality of elements as described above, there being lines of weakening which form the boundaries of said elements and along which individual elements can be detached from said sheet.

The above described element can be of white opaque synthetic plastics material.

According to a still further aspect of the present invention there is provided a method of testing the pH of a soil sample, which method comprises mixing the soil sample with sufficient water to saturate the soil and form a water layer above it, agitating the mixture, allowing the soil to settle out of the layer of water, using a rod to lift a drop of water from the layer of water, and placing the drop into a depression which is coated with pH indicator.

According to another aspect of the present invention there is provided a nitrogen testing element which is of water impervious sheet material with a depression therein, the depression being coated with an indicator which changes colour in response to the nitrogen content of a water sample placed in the depression.

According to yet another aspect of the present invention there is provided a method of testing the nitrogen content of a soil sample, which method comprises mixing the soil sample with sufficient water to saturate the soil and form a water layer above it, agitating the mixture, allowing the soil to settle out of the layer of water, using a rod to lift a drop of water from the layer of water, and placing the drop into a depression which is coated with an indicator which changes colour in response to the nitrogen content of the water sample.

For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawing in which: Figure 1 illustrates a sheet comprising a number of pH testing elements, and Figure 2 is a section on the line ll-ll of Figure 1.

The sheet 10 illustrated is preferably of synthetic plastics material but can be of any other water impervious material. The sheet is formed with a plurality of lines of weakening designated 12 which divide the strip into a plurality of pH testing elements 14. Each element has two depressions 16 therein. Each depression is coated with a pH indicator designated 18 in Figure 2.

A large number of pH indicators are available commercially, such indicators changing colour in dependance on the pH of the solution which is applied to them. Indicators are commercially available which are relatively insensitive to pH changes over one part of the pH range but which are extremely sensitive to pH changes over another part of the range. One of the depressions 16 of each element 14 is coated with a pH indicator which changes colour rapidly with pH changes in the range of, say, 6 to 7.5, and the other depression 16 is coated with an indicator which changes colour rapidly in the range of 5 to 6.

The structure described and illustrated is intended primarily for the purpose of determining the pH of a soil sample. The soil sample is placed in a glass jar or other container and tap water run in until there is a layer of water above the thoroughly saturated soil. The water and soil are agitated by stirring or shaking. The water does not have to be neutral pH because, with the quantity of soil used in the test, the water rapidly takes on the pH of the soil. The water-soil mixture is then allowed to stand so that the soil particles which the shaking or stirring have left in suspension settle out. The layer of water above the soil after, say, about 20 minutes becomes sufficiently clear for test purposes. A small amount of material still in suspension does not have a substantial effect on the result obtained.Clay soils are somewhat more difficult to test as clay will stay in suspension for prolonged periods of time. To overcome this problem a small quantity of barium sulphate can be mixed with the soil.

The barium sulphate has the effect of causing the clay particles to settle rapidly. A small amount of aluminium oxide can be dispersed in the barium sulphate.

One of the elements 14 is torn form the sheet 10 for use. A rod is then dipped into the clear water above the soil without disturbing the soil. When the rod is withdrawn one drop water remains on the end of the rod. This drop is then placed in one of the depressions 16. The depressions 16 are sized so that the drop of water that would normally form on the end of stick 1 which was, say, 2mm across, would substantially fill the depression. Depending on the pH of the water, the pH indicator in the depression 16 changes colour. Another drop of water is placed in the other depression 16.

The elements 14 are used in conjunction with a colour chart which is printed with pairs of dots.

Each pair of dots represents the colour that the coatings 18 will take-on when subjected to a partic ular pH. By comparing the colours of the coatings 18 with the dots on the chart, a reaonably accurate determintion of pH can be made.

Because it is possible with the present invention to readily use two indicators which are sensitive to pH variations in different parts of the pH range, accurate determination of pH is possible. One coating is chosen so that it is very sensitive to acid soils and its colour change will indicate accurately their pH. The other coating is relatively insensitive to changes in the pH of an acid soil but changes rapidly in colour with relatively small changes in the pH of an alkaline soil. Of course, it is possible to have a single depression 16 coated with indicator, but then sensitivity is lost.

The sheet 10 is preferably of white material so that the coating in the depressions 18 is being viewed against a white background. The colour chart is itself printed on white paper and hence the user is attempting to compare a printed area on a white background with a coloured coating against a white background. There is thus considerable similarity between the two. This is in contradistinction to prior art methods where the user is attempting to compare a translucent coloured liquid with a printed area.

The indicator sheet described can, be changing the nature of the coating 18, also be used to determine the nitrogen content of the water above the soil. A chart can be provided which has coloured areas indicative of various nitrogen contents. In this form only one depression 16 is needed.

It will be understood that, if desired, each element 14 can have three depressions in it. Two are for use in connection with pH determination and one for use in nitrogen content determination A kit of this form is thus a dual purpose one. Of course, in the same kit, there can be sheets 10 intended solely for pH testing and other sheets for nitrogen testing. Alternatively, it is possible to provide separately packaged single purpose kits.

The soil and water are preferably mixed in a small container having graduation marks which show the level to which the container must be filled with soil and the level to which it must thereafter be filled with water. A third graduation mark ciose to the base of the container indicates the barium sulphate level.

Claims

1. A pH testing element which is of water impervious sheet material with a depression therein, the depression being coated with a pH indicator.

2. An element as claimed in claim 1 and which is of elongate rectangular form with the depression near one end thereof and the other end forming a gripping portion.

3. A pH testing element as claimed in claim 1 or 2 and which has two depressions therein, the depressions being coated with two different pH indicators.

4. A kit including a plurality of elements as claimed in claim 1, 2 or 3, and a colour chart printed with areas showing the colours taken-on by said pH indicator(s) in response to the application thereto of water of varying pH.

5. A kit as claimed in claim 4 and also including a rod which can be dipped into the water being tested so as to pick up a drop of water which can be placed in said depression(s).

6. A sheet comprising a plurality of elements as claimed in claim 1,2 or 3, there being lines of weakening which form the boundaries of said elements and along which individual elements can be detached from said sheet.

7. An element as claimed in claim 1, 2 or 3 and which is of white opaque synthetic plastics mate rial.

8. A method of testing the pH of a soil sample, which method comprises mixing the soil sample with sufficient water to saturate the soil and form a water layer above it, agitating the mixture, allowing the soil to settle out of the layer of water, using a rod to lift a drop of water from the layer of water, and placing the drop into a depression which is coated with a pH indicator.

9. A nitorgen testing element which is of water impervious sheet material with a depression therein, the depression being coated with an indicator which changes colour in response to the nitrogen content of a water sample placed in the depression.

10. A method of testing the nitrogen content of a soil sample, which method comprises mixing the soil sample with sufficient water to saturate the soil and form a water layer above it, agitating the mixture, allowing the soil to settle out of the layer of water, using a rod to lift a drop of water from the layer of water, and placing the drop into a depression which is coated with an indicator which changes colour in response to the nitrogen content of the water sample.

11. A soil testing element substantially as hereinbefore described with reference to the accompanying drawing.