42. ° REPORT—1863. 
weight of strong acid to six parts of the chloride. The mixture so obtained is 
heated strongly until all the hydrochloric acid is expelled and the residue assumes 
the form of a dense liquid. ‘I'his, being set aside, solidifies on cooling to a white 
crystalline mass. When this is dissolved in water an immense amount of heat is 
evolved, and great care must be taken to avoid breakage of the vessels. The best 
way of dissolving it is to add it slowly to ten times its weight of hot water. A 
solution is thus obtained, which must be filtered; and on being concentrated and 
set aside to cool, crystals of sulphate of thallium will be obtained, which may be 
rendered quite pus by recrystallization,—a little hydrosulphuric acid being pre- 
viously added, if necessary, to separate arsenic, mercury, &c. 
The final step in the process is the reduction of the metal from this sulphate, 
Plates of pure zinc (which must leave no residue whatever when dissolved in sul- 
phuric acid) ave arranged vertically round the sides of a deep porcelain dish hold- 
ing a gallon. About seven pounds of crystallized sulphate of thallium are then 
placed in the dish, and water poured over to cover the salt. Heat is applied, and 
in the course of a few hours the whole of the thallium will be reduced to the state 
of a metallic sponge, which readily separates from the plates of zinc on slight 
agitation. The liquid is poured off, the zincs removed, and the spongy thallium 
washed two or three times. It is then strongly compressed between the fingers, 
and preserved under water until it is ready for fusion. The fusion of the metal 
is readily effected. An iron crucible is placed over a gas-burner, and a tube is 
arranged so that a constant stream of coal-gas may flow into the upper part of the 
crucible. Lumps of the compressed sponge are then introduced, one after the other 
as they melt, until the crucible is full of metal. It is then stirred up with an iron 
rod, and the thallium may either be poured into water and obtained in a granu- 
lated form, or cast into an ingot. Thirty or forty fusions have been performed in 
the same crucible without the iron being acted upon in the least by the melted 
thallium. The products of these fusions were ultimately melted together and cast 
in an iron mould. The bar of metallic thallium exhibited before the Section 
weighed a quarter of a hundredweight. 
Thallium contracts strongly on cooling. The coating of tarnish which it 
acquires while hot is instantly removed by water, which renders the surface per- 
fectly bright. The liquid metal in the crucible, when protected by the stream of 
coal-gas, can scarcely be distinguished from mercury. Thallium is not absolutely 
identical in colour with any other metal, but approaches nearest to cadmium and 
tin. It has perfect metallic lustre. “Its specific gravity is 119. It is very malle- 
able, but not very ductile. It can only be drawn into wire with great difficulty ; 
but by the operation technically known as squirting, thallium wire may be formed 
most readily. Thallium is very soft, being only exceeded in this property by the 
alkali metals. A point of lead will scratch thallium with the greatest readiness. 
Thallium possesses the property, in common with soft metals, of welding by pres- 
sure in the cold. Rubbed on paper, it gives a dark streak, having a yellow reflec- 
tion, which in a short time nearly fades out, but may be restored with an alkaline 
sulphide. Thallium is strongly diamagnetic, being in this oe nearly, if not 
quite, equal to bismuth. It melts at 550° F., and distils at a white heat, evolving 
brown vapours into the air at a temperature little above its melting-point. When 
a minute fragment of thallium, or of any of its salts, is introduced into the flame 
of a spirit-lamp, it colours it of a most intense green, which, when examined by 
means of a spectrum apparatus, appears to be absolutely monochromatic, com- 
municating one single green line to the spectrum. This property of the metal is 
now too well known to require further remarks; from it the name Thallium was 
chosen. 
The atomic weight of thallium is 203. This result, however, is not deduced 
from sufficiently accurate analyses to render it entirely trustworthy, and the author 
is now engaged in determining the equivalent in a more accurate manner. 
On Photelectrie Engraving, and Observations upon sundry Processes of Photo- 
graphic Engraving. By Duncan C, Dattas, 
