A Methods Manual for the Collection, Preparation and Analysis of ...

1.4 Other methods (Incineration)The above methods (1.3.1 – 1.3.4) will completely destroy the organic material both insideand outside of the diatoms cells including the organic materials used for colony formation.Thus, by using these methods it will only be possible to observe single cells in the finalpreparations. To make permanent slides which retain colony formation requires the use of adifferent technique known as incineration. This technique may also be useful for particularlydelicate and weakly silicified diatoms that would be destroyed or badly damaged using othertechniques. The technique of incineration is described below:Place 2-3 drops of fresh concentrated diatom suspension onto a coverslip.Add distilled water until the surface of the coverslip is almost covered.Gently heat the coverslip on a hot plate until all the liquid has evaporated.Increase the heat to 350°C and continue to heat the sample.Watch carefully for the changes in the colour of the diatom material.The sample will first become brown as the chlorophyll and other organic material isincinerated.The sample will then turn black as all the organic material is converted into carbon.As the carbon is incinerated the remaining material will turn a whitish colour.When the sample is clean, i.e. has a white appearance, allow the coverslip to cool andremove it from the hotplate.Gently rinse the upper surface of the coverslip to remove any salts or other precipitates.Heat the coverslip again until all the moisture has been removed from the sample.The sample is now ready for mounting in a high resolution diatom mountant.34