Faraday to Benjamin Hawes   13 December 1847

Royal Institution | 13 Decr. 1847

My dear Sir

I have not occupied myself with coal gas for some time but I think the means you tell me of as applied to purification must be quite sufficient if the process be attended to & the charges changed in sufficient time. If you render your gas pure as regards sulphur & ammonia still being afterwards sent through old pipes or gazometers or gas meters it may take up these impurities again.

The tests you speak of are quite sufficient, but will you allow me to suggest that perhaps a useful change over those who are entrusted with the purifying process might be obtained by having the test paper for sulphuretted hydrogen or sulphur compounds put into the gas passage at a place prior to the delivery to the public & after it has left your gazometer in such a manner that though it should be visible it should not be removable except by some one deputed to observe the effect it might exhibit. I write privately & may therefore tell you that I know of a party in Regent street who left another company & went to your mains that they might have better gas - who at first found the gas unexceptionable being quite free from sulphur but within the last 2 or 3 months a little sulphur has appeared. This was not due to a foul gas meter for that has been taken down & washed & refitted & yet the gas continues not so good as it was.

Rejoicing in the thoughts of your health & activity I am | My dear Sir | Very Truly Yours | M. Faraday

Benjn Hawes Esq | &c &c &c