Thallous halides

Thallous fluoride, chloride, bromide, and iodide are all known. The last three salts resemble the corresponding compounds of lead very closely in appearance and in physical properties; it has been both affirmed and denied that in the liquid state they have the properties of liquid crystals. The molten chloride and bromide have not been obtained optically clear.

Thallous chloride, bromide, and iodide are miscible in the liquid state, and the three systems TlCl - TlBr, TlBr - TlI, and TlCl - TlI have been studied by the thermal method. The results show that the first two systems yield continuous series of mixed crystals, the " liquidus " curves exhibiting minima, and that the last system forms an incomplete series, the "liquidus" exhibiting a transition-point.