Faraday to Jacob Herbert   21 April 1855

Royal Institution | 21 April 1855

My dear Sir

The waters are both very bad¹. That from the House tap contains lead in solution, and there was a little deposit of lead at the bottom of the bottle. The water contains also Sea salt. I do not know where it comes from, but it is so free from the solutions usually occurring in common waters, & so peculiar in respect of the common salt & lead, that I think it must be rain water gathered upon a leaden roof,- within reach of the spray of the sea. Water so gathered will always be dangerous: for the purity of the water in respect of earthy salts & the presence of the marine salt both tend to make it act upon lead.

The other specimen labled Brack tank water is very bad indeed. When poured out it was milky from the suspension of hydrate & carbonate of lead in it; & there was much dirty deposit at the bottom, which was chiefly carbonate of lead. This deposit is probably lead which has formerly been in solution:- when it has once been deposited & has settled at the bottom of the tank it does no harm to the water, unless it be stirred up & mixed with it, though it is always a sign that the water has at one time or other been poisoned by it. But that which is diffused through the water & that which is dissolved, are both dangerous. I do not know what relation this water has to the former, but from the likeness of character in many respects, suppose it is the former water collected in a brack tank. The change to an opalescent state & the gradual deposition of carbonate of lead accord with such a supposition[.]

I am | My dear Sir | Yours Very truly | M. Faraday

Jacob Herbert Esqr | &c &c &c