From Edward Frankland   16 October 1873

My dear Sir,

The litmus paper possesses what chemists call a neutral tint.¹ It is very sensitive to acids & still more so to alkalies. The longer piece which I return has been half immersed in a mixture of 1 part of sulphuric acid and 100,000 parts of water. I know not in what condition it may reach you but, as I write, the difference of tint (bright red & port wine red) is so strong, that, it can scarcely be doubted, a very much smaller proportion of acid could be detected.

You will find that the paper will most distinctly indicate the alkalinity of any chalk-spring or well water that you may have in your neighbourhood.

If you would like some bluer but less delicate, I shall have great pleasure in sending you some & would do so now but do not happen to have any at hand as I write.

Believe me | Yours sincerely | E. Frankland.