GB2235289A - Method of testing for lead - Google Patents

Abstract

A method of testing for lead in an article, the method comprising forming an aqueous solution with an acid pH in the range 1-5, bringing this solution into contact with the article, adding a sulphide containing compound to the solution, the compound being of a type which produces a colourless sulphide solution, and visually examining the resulting solution for a lead sulphide precipitate indicating the presence of lead.

Description

Improved Testing for Lead The present invention relates to an improved method for testing for lead, and particularly but not exclusively to a method of testing for lead in the range 4 to 40 p.p.m. in glazes on ceramic wear or paint.

A number of people have been poisoned when consuming acid foods which have been stored in pottery containers the glaze of which includes lead leachable by acid foods. Further, people and especially young children have ingested lead from old paintwork. Whilst tests are available to determine the lead content of such glazes and paints, these tests are relatively complex and expensive and are thus not suitable to be carried out in the home.

According to the present invention there is provided a method of testing for lead in an article, the method comprising forming an aqueous solution with a pH in the range 1-5, bringing this solution into contact with the article, adding a sulphide containing compound to the solution, the compound being of a type which produces a colourless sulphide solution, and visually examining the resulting solution for a lead sulphide precipitate indicating the presence of lead.

Preferably the aqueous solution has a pH in the range 2-4.

The aqueous solution may be formed from an organic acid. This acid may be selected from the group consisting of citric, tartaric, maleic, adipic; succinic, propionic, and lactic. Preferably the aqueous solution is white distilled vinegar.

Preferably the sulphide solution forms between 1 and 50pro by weight of the resulting solution and desirably this figure is in the order of 5.

Preferably the sulphide containing compound is selected from the group consisting of sulphides and hydrosulphides of lithium, sodium, potassium, ammonium, calcium, strontium and barium.

Embodiments of the present invention will now be described by way of example only.

Example 1 0.5 millilitres of 5 by weight sodium sulphide nonahydrate in water was added to 50 millilitres of white distilled vinegar containing 7 p.p.m. of elemental lead. A brown colour was immediately visible. This test was repeated with vinegar which was free of lead and no colour or darkening was discernable.

Example 2 4.15 millilitres of a 5 by weight aqueous solution of sodium sulphide nonahydrate was added to a solution of 50 millilitres of 5 by weight acetic acid in water containing 200 milligrams of instant coffee granules and 7 p.p.m. lead. Within about 15 seconds the lead sulphide was visually identifiable.

Example 3 An Italian coffee mug was filled with white distilled vinegar and allowed to stand uncovered at room temperature for 24 hours. The vinegar was poured from the mug 'into a white container and 0.25 millilitres of 5 aqueous sodium sulphide nonahydrate solution was added. A dense black precipitate was visible. Further conventional tests indicated that the mug contained considerable amounts of acid soluble lead.

It is to be realised that a wide variety of chemicals can be used to perform this test other than those given in the examples. If it is required to test painted surfaces, a sample of the surface can be taken by filing or otherwise and placed in a suitable container. Printed samples illustrating the colour of lead sulphide precipitate obtained for varying lead concentrations may be provided. An assembly may be provided including such samples alongside a container for carrying out the test to allow ready comparison of any precipitate obtained.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims (9)

Claims:

1. A method of testing for lead in an article, the method comprising forming an aqueous solution with a pH in the range 1-5, bringing this solution into contact with the article, adding a sulphide containing compound to the solution, the compound being of a type which produces a colourless sulphide solution, and visually examining the resulting solution for a lead sulphide precipitate indicating the presence of lead.

2. A method according to claim 1, in which the aqueous solution has a pH in Lhs range 2-4.

3. A method according to claim 1 or 2, in which the aqueous solution is formed from an organic acid.

4. A method according to claim 3, in which the organic acid is selected from the group consisting of citric, tartaric, maleic, adipic, succinic, propionic, and lactic.

5. A method according to claim 3, in which the aqueous solution is white distilled vinegar.

6. A method according to any of the preceding claims, in which the sulphide solution forms between 1 ó and 50 Ó by weight of the resulting solution.

7. A method according to claim 6, in which the sulphide solution forms in the order of 5 by weight of the resulting solution.

8. A method according to any of the preceding claims, in which the sulphide containing compound is selected from the group consisting of sulphides and hydrosulphides of lithium, sodium, potassium, ammonium, calcium, strontium and barium.

9. Any novel subject matter or combination including novel subject matter disclosed in the foregoing specification or claims and/or shown in the drawings, whether or not within the scope of or relating to the same invention as any of the preceding claims.