These are made of soda glass. They are individually matched at the Sherwood factory and supplied in matched sets, i.e. each tube in any set has exactly the same absorbance characteristics, this ensures that once a blank has been measured every sample absorbance readout will be due to the sample only no matter which of the tubes in the set is used.
Various diameter tubes are offered so that the sensitivity of measurement can be varied i.e., if a sample is concentrated (high absorbance values) then measurement in a small test tube is suitable as the light has to travel a smaller distance through the sample leading to lower absorbance values. However if dilute samples are to be analysed it is necessary to increase sensitivity by offering more sample to the light hence larger test tubes are used.
Each test tube size has a corresponding holder. The holders can also accommodate a square cuvette of the appropriate size as indicated in the table
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