Note 757 — PART IX.—INORGANIC POISONS.
Reading edition
Otto recommends the first half of the drying tube connected with the development flask to be filled with caustic potash, the latter half with chloride of calcium (Ausmittelung der Gifte). Dragendorff approves of this, but remarks that it should be used when arsenic alone is searched for, since caustic potash decomposes stibine. The potash fixes SH2, and prevents the formation of chloride of arsenic; on the other hand, it absorbs some little AsH3.
[758] For identification of arsenical films, see p. 557.