R Institution | May. 31st / 32
My dear Sir
You are quite right in your recollection of sulphate of baryta precipitate[.] I have had that substance in suspension under particular circumstances for 18 or 24 hours together in glasses not containing more than four inches of water & the liquid turbid even at the end of that time1[.]
But I cannot express even generally how long a particular substance or a fine precipitate takes to settle for the same substance varies very much according to the circumstances under which its particles have aggregated & become solid in smaller or larger masses[.]
As you are considering the suspension of solid particles for a longer or shorter time according to their magnitude, are you aware that Girard2 has something particular about the influence of solid particles in liquids[.] I have referred to it at p 60 of my Manipulation 2nd Edition3 but you will find his paper in the Mem de l'Académie Royale. IV. 1819. 18204[.]
Oxide of tin made by pouring nitric acid on tin foil is when rubbed so fine a powder it can hardly be washed in any reasonable time in pure water[.] Add salt to the water which increases the S.G. & the oxide separates far more readily.
Ever Dear Sir | Very Truly Yours | M. Faraday
C. Babbage Esq | &c &c &c
I send you two pennyworth of Manufacture. The things are made at Nuremburg, sent here and sold retail with a profit for the above small sum[.] I think there are 30 pieces including box & lid[.]
FARADAY, Michael (1830b): Chemical Manipulation, being instructions to students in chemistry, on the methods of performing experiments of demonstration or of research, with accuracy and success, 2nd edition, London.
GIRARD, Pierre-Simon (1819): “Mémoire sur les atmosphères liquides, et leur influence sur l'action mutuelle des molécules solides qu'elles enveloppent”, Mém. Acad. Sci., 4: 1-98.
Please cite as “Faraday0584,” in Ɛpsilon: The Michael Faraday Collection accessed on