Faraday to Jacob Herbert   13 January 1847

Royal Institution | 13 January 1847

My dear Sir

I have examined the Bardsey water refered to in your letter of the 9th instant¹ and as to saline matter there is nothing in it which is likely to make it unwholesome though there is sufficient to make it rather hard. But there is a substance partly of an organic nature which I do not at present recognize and which being in small quantity I cannot examine sufficiently without more of the water. I should be glad of as much as a gallon of the water for that purpose but it ought to be drawn in clean vessels & enclosed in a clean bottle stopped by clean cork. I should like to know also how the well is situated in respect of any near drain or cesspool or duty ditch.

In reference to the oil question I do not know of any mode of analysis or chemical treatment that will serve as a test before hand of the purity of the oil or fitness for burning. The oil ought no doubt to be clear & have the other appearances known to belong to good oil but occasionally specimens which will not burn well will present the same appearances & then burning alone is the sufficient test of their quality. When I was amongst the French lighthouses² I enquired particularly as to their mode of recognizing the fitness of the Colza oil sent to them & the keepers (& M Fresnel also) informed me that the responsibility was cast upon the contractors that the portions supplied being kept separate if any one burnt badly the whole was sent back at the contractors expence & risk. This is not an urgent process for if the contractor prepares his oil always in the same way & with equal care he will always have the same result and he of all persons can most easily tell whether his oil is good & he prepared to be responsible for it³.

I am My dear Sir | Yours most faithfully | M. Faraday

Jacob Herbert Esq | &c &c