Faraday to John Barrow   17 February 1830¹

Royal Institution | Feb. 17. 1830

Dear Sir

I have carefully examined the three samples of water which you sent to me for the purpose² and certainly find that the sample distilled by ordinary boiling from sea water is purer than that prepared by the process of M de Santune³ &c. They are nearly the same with respect to Muriate of Soda for though both contain traces yet the latter contains the most[.] But the great difference consists in the presence of Sulphate of lime in the latter from which the former is free[.]

The quantity of saline matter in the distilled water obtained by M de Santune’s process is very small and not more than occurs in some very pure & fine spring waters; and the water may in that respect be considered as very fit for domestic purposes[.] I know of no difficulty however in the way of obtaining such water at pleasure by the distillation of Sea water and have frequently had occasion to examine specimens obtained by the distillation of sea water in the ordinary way by myself and others which were purer than either of those you sent to me. The difficulty if there be one is not in obtaining the water pure but in performing the operation by the smallest possible quantity of fuel.

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

John Barrow Esq | &c &c &c