Analytical Methods:Field Carbonate Determination
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Contents |
[edit] Calcium carbonate determination
based on the method of the Soil Survey of England and Wales ([Hodgson, 1976>Main.Glossary.Reference.Hodgson1976])
| Scale | A quick, field-based analysis to confirm the presence and quantity of calcium carbonate (up to 10%). |
| Questions | On-site confirmation of calcium carbonate in soil, sediments and artefacts (destructive). |
| Samples and storage | Fresh, field samples |
| Time and cost | Very quick, low cost |
| General comments | No specialist knowledge required. |
[edit] Questions
On-site confirmation of calcium carbonate in soils, sediments and artefacts. This technique can be used to:
- Determine whether areas colour differences (greyness) reflect different depositional contexts or whether they have been affected by post-depositional calcium carbonate formation.
- Identify the presence of limestone and other calcareous stones in soils and sediments.
- Identify deposits where shell and bone preservation should be good (should be used in combination with soil pH).
[edit] Method
[edit] Required equipment and chemicals1
- 1M HCl (1 molar Hydrochloric acid)
- Dropping dispensing bottle
Make the acid by mixing 1 part concentrated HCl1 (37%) with 11 parts distilled water. Always add the acid to the water and not the other way round.
[edit] Method
Take a small sample (ca. 1 g) of the deposit and apply a drop or two of acid. Watch and listen (hold close to the ear) for a reaction as bubbles of carbon dioxide gas are produced (effervescence). Alternatively the acid can be applied to a particular soil feature or coating of interest.
| Carbonate content | Visible effects | Audible effects |
|---|---|---|
| Non-calcareous (less than 0.5%) | No bubbles form | No audible reaction |
| Very slightly calcareous (0.5-1%) | No bubbles form | Slight audible reaction |
| Slightly calcareous (1-2%) | Very few bubbles form, confined to individual grains and just visible | Moderately audible reaction |
| Slightly calcareous (2-5%) | Few bubbles form | Moderately to distinctly audible; can be heard away from the ear. |
| Calcareous (5-10%) | Many obvious bubbles form up to 3 mm diameter | Easily audible away from the ear |
| Very calcareous (more than 10%) | Very many bubbles form up to 7 mm diameter | Easily audible away from the ear |
[edit] Data and interpretation
This is a semi-quantitative analysis in soils or sediment containing up to 10% calcium carbonate. The percentage content cannot be further quantified above 10%.
Dolomite (Calcium magnesium carbonate) reacts only weakly with 1M HCl, but will visibly react with 6M HCl1 (1 part concentrated HCl to one part distilled water). However, the reaction cannot be quantified as for calcium carbonate.
[edit] Safety
1 Always consult chemical safety data sheets and follow appropriate health and safety protocols before handling or using chemicals.
Many chemical safety data sheets are available here from this Oxford University based database.
[edit] Related Techniques
