40

[in margin:] I have only just alluded to this in Ch. I

Sand is rendered pale by immersion for some weeks in diluted muriatic acid — The tiles not affected, but not tiles (I cannot avoid feeling rather sceptical whether the discoloured bits were really tiles or not pale brick accidentally in soil) I must not give tiles without further evidence as were added very little before worms dissolved & I think bits of brick given before) I have now (Dec 21) compared some bits of tiles got out of castings in Pots V & VI with fresh tiles soaked in water, & the former appear (& when broken) a shade duller red.

Jan 6 1881 Sand & tiles now left immersed for several weeks in diluted nitric & sulphuric acids — Tiles not affected — Sand much yellower in the Sulfuric & only slightly

[in margin:] Last chapter

40v

& only slightly yellower in the nitric acid, but in both still much oxide of iron clinging to grains — The watch-glasses were compared with fresh sand in water — Certainly the digestive fluid seems to act more powerfully on the oxide of iron in the sand than in the several acids tried.

"The acids in the castings seemed also more efficient as seeming to cover then even diluted (according to M [illeg]) sulphuric, nitric or hydrochloric acids.