Faraday to Peter Henry Berthon   16 February 1863

Royal Institution | 16 Feby. 1863.

Sir

I have examined the three red leads which you sent me with your letter of the 10th instant¹[.] No adulterative substance that I can discover has been added to any of them, and as far as I can judge they are, as regards their manufacture, unexceptionable; but I do not profess to be a judge in that respect of the superiority of one sample over another.

As to the four white leads. The specimens marked Pilcher and Pontifex & Wood contain nothing that can be accounted as impurity or adulteration. The other two specimens contained small quantities of matter not white lead. That in Crace & Co ² amounts to 0.15 in 100 parts or 1 in about 650. That in Tudor amounts to 1 in 500 parts. I do not think that in these specimens, they had been added as adulterations; - in both cases it was sul baryta or heavy earth which had crept in probably in the grinding.

I have not estimated the proportion of oil in these four specimens. I do not consider it an important matter in relation to adulteration, & it would have taken me much more time to ascertain it, than I could spare before going the lighthouse tomorrow. Crace & Co seemed to have the largest quantity and Tudor to be the driest³.

I am Sir | Your Very Obedient Servant | M. Faraday

P.H. Berthon Esqr | &c &c &c