TBANSACTIONS OF THE SECTIONS. ’ 4d 
factured, are capable of resisting the greatest heat—always contain a large portion 
of silica. The preceding Table contains a series of analyses of samples of fire-clay 
taken from seven seams, all worked in the mines belonging to one fire-brick ma- 
nufactory, situated a few miles west of Newcastle. 
The remaining part of the paper treated at length of the various applications 
which have been found, especially in late years, for articles made from this 
substance. 
On the Extraction of Thallium on a large scale from the Flue-dust of 
Pyrites-burners. By W. Crooxgs, F.R.S. 
gen some months past been occupied, in conjunction with Messrs. Ege 
kin and Williams, in the extraction of thallium from an amount of material far 
greater than has ever been treated before, the author proposed to bring before the 
Meeting an account of the methods ultimately adept 
The author has received some hundreds of specimens of deposit, flue-dust and 
minerals, every one of which was first of all easel tested for the metal by means 
of the spectroscope. The practical employment of spectrum analysis is, he regretted 
to say, of but very limited use, and has caused him many disappointments before he 
determined to abandon it, except for confirmation in subsequent experiments. The 
spectrum by itself pines no indication of quantity; the green line produced by a 
residue containing but one part of thallium in a thousand is as vivid and distinct 
as the line given by the pure metal; and therefore, before he could decide whether 
a deposit contained sufficient thallium to repay for its extraction, it was necessary 
to make an estimation in the moist way, by exhausting a weighed quantity of the 
dust with water, and adding hydrochloric acid to the solution. Associated with 
thallium in these deposits is, unfortunately, a variety of other metals, among which 
he found mercury, copper, arsenic, antimouy, iron, zinc, cadmium, lime, and sele- 
nium, together with ammonia, sulphuric, hydrochloric, and nitric acids. 
Soon after the publication of Fis lecture delivered at the Royal Institution, 
March 27, 1863, Dr. Alfred S. Taylor sent me a powder, which is, beyond doubt, a 
portion of the residue in which Berzelius found selenium. He examined the speci- 
men with the most scrupulous care in the spechraseore: but have been unable to 
-see the faintest trace of the green line. Had thallium been present, it would 
scarcely have escaped the keen observation of Berzelius. 
. The flue-dust upon which we have a3 yet operated amounts to about five tons, 
the whole of which has been treated by the method he is about to describe. The 
difficulties of manipulating such an amount have been very serious. The process 
at present adopted at Messrs. Hopkin and Williams’s laboratory is as follows :— 
The thalliferous dust is first treated in wooden tubs with an equal weight of boil- 
ing water, and is well stirred. During this operation a considerable quantity of 
nitrous acid is evolved; after which the mixture is allowed to rest for twenty-four 
hours for the undissolved residue to deposit. The liquid is then siphoned off, the 
residue is washed, and afterwards treated with a fresh quantity of boiling water. 
The collected liquors which have been siphoned off from the deposit are allowed 
to cool, precipitated by the addition of a considerable excess of strong hydrochloric 
acid, at the precipitate, consisting of very impure chloride of thallium, is allowed 
to subside. The chloride obtained in this way is then well washed on a calico 
filter, and afterwards squeezed dry. He mentioned that from three tons of the 
dust he obtained 68 pounds of this rough chloride. 
The next step consists in treating the crude chloride in a platinum dish with an 
equal weight of strong sulphuric acid, and afterwards heating the mixture to expel 
the whole of the hydrochloric acid. To make sure of this, the heat must be con- 
tinued until the greater part of the excess of sulphuric acid is yolatilized. After 
this the mass of sulphate of thallium is dissolved in about twenty times its weight 
of water, and the solution filtered. On the addition of hydrochloric acid to this 
solution, nearly pure chloride of thallium is thrown down; this is collected on a 
“calico filter, well washed, and then squeezed dry. 
It is now necessary to again convert the chloride into sulphate. For this pur- 
pose we add the dry chloride gradually to hot sulphuric acid, using four parts by 
