| 7 St. Mary's Road, Canonbury, | July 21, 1856.
MY DEAR TYNDALL,
In an account of your lecture ‘On the Cleavage of Crystals and Slate Rocks’ (Phil. Mag. vol. xii. p. 46),1 you have noticed my experience in the consolidation of precipitated white lead, and have correctly stated the unfavourable results of my first attempts with conical moulds.2 It may be of interest to the readers of the Philosophical Magazine to learn that the difficulty was entirely overcome by substituting cylindrical moulds. By their employment the lateral spread of the mass was prevented, and cakes of white lead3 were produced which broke with a conchoidal fracture,4 and which consequently could readily be ground to a granular powder.
I am, | Yours very truly, | WARREN DE LA RUE.
Phil. Mag., 12 (1856), p. 1575
Phil. Mag. vol. xii, p. 46: J. Tyndall, ‘Comparative View of the Cleavage of Crystals and Slate Rocks’, Phil. Mag., 12 (1856), pp. 35–48.
conical moulds: In his paper (n. 1), at p. 46, Tyndall had stated: ‘As time passed on cases multiplied, illustrating the influence of pressure in producing lamination. Mr. Warren De la Rue informs me that he once wished to obtain white-lead in a fine granular state, and to accomplish this he first compressed the mass: the mould was conical, and permitted the mass to spread a little laterally under the pressure. The lamination was as perfect as that of slate, and quite defeated him in his effort to obtain a granular powder.’
cakes of white lead: basic lead carbonate used as a white pigment in oil painting and as the basis of domestic paints.
conchoidal fracture: The fracture of minerals or rocks such that they have smooth convex or concave surfaces.
Published under the title, ‘CLEAVAGE OF COMPRESSED WHITE LEAD’.
Please cite as “Tyndall1257,” in Ɛpsilon: The John Tyndall Collection accessed on