Ordinary Meeting, October 16th, 1866. 
Edward Schunck, Ph.D., F.R.S., &c., President, in the 
Chair. 
“ On the Isomorphism of Thallium-perchlorate with the 
Potassium and Ammonium-perchlorates,” by Prof. H. E. 
Roscoe, F.R.S., &c. 
The recently ascertained isomorphism of the Thallium- and 
Ammonium-sulphates* renders it highly probable that the 
perchlorates of these metals also exhibit isomorphous rela- 
tions. 
Thallium-perchlorate equals the Alkaline-perchlorates in 
stability. It can be readily prepared either by dissolving 
metallic Thallium in aqueous Perchloric Acid, or by the 
double decomposition of Thallium-sulphate and Barium- 
perchlorate. From solution the anhydrous Salt is easily 
deposited in colourless rhombic crystals, which are trans- 
parent, bright, well-defined, and non-deliquescent. The 
specific gravity of the crystals is 4*844 at 15°*5 C.; they dissolve 
in 10 times their weight of water at 15°, and in about -fths of 
their weight of water at 100° ; the salt is also slightly soluble 
in alcohol. Thallium-perchlorate does not lose weight when 
heated to 200° C., and the temperature may even be raised to 
* Lang, Phil. Mag., xxv. 248. 
Proceedin' GrS — Lit. & Phil. Society. — Yol. VI. — No. 2 — Session 1866-7. 
