‘Think twice about adding fluoride' is the alarmist claim by Dr Janice Priest of Herbal Ltd (The Weekend Sun, May 9), but she then lets herself down with her lack of scientific knowledge. She claims sodium fluoride is an industrial by-product.

So what? Marmite is a by-product of yeast production and butter a by-product of milk. It also occurs naturally in the mineral villiamite.

She then seems to try to vilify hydrofluosilic acid by stating it is inorganic. Inorganic simply means it doesn't contain carbon, neither does water for that matter.

She then writes the formula for hydrofluosilic acid is SiF6. It isn't, it is (H3O)2SiF6.
This hardly inspires one to have much confidence in the validity of the rest of her claims.
She signs herself as Dr - a doctor of what she doesn't say but it certainly can't be in chemistry.

R Prince, Welcome Bay.