From JOHN VINE
Andy Coghlan (Forum, 5 June) must have some difficulty making coffee at home
if he can dissolve 1 gram of coffee in a kettleful of water and achieve a
concentration of 1 milligram of coffee per litre of water. When full, his
kettle must weigh around 1 tonne and would be hard to lift onto the stove.
It should also be noted that 1 milligram per litre is, in fact, 1 part per
million and not, as stated, one part per thousand.
To get a rough idea of what 1 part per billion represents, imagine a
teaspoon of sugar dissolved in an Olympic swimming pool.
John Vine
Doncaster, Australia
