278 
ON THE EXTRACTION OF THALLIUM. 
ottoes which are colourless when first obtained from their source become yellow 
by age, i. e. oxidation. This however, is not universal, as the otto of nutmeg 
remains colourless for a lengthened period, even when air is drawn through it by 
an aspirator. 
The oxidized portion of the yellow-coloured oils, when separated from the pure 
otto in which it is dissolved, are true resins; the majority of ottoes oxidize during 
the act of distillation, hence from this cause they vary in colour from pale-yellow 
to red-brown. When new, that is, freshly distilled, several essential oils are of a 
pale-green, but indicating the presence of azulene; but as oxidation proceeds, 
the yellow resin generated conceals the azulene. We have— 
A. Ottoes which are colourless, containing neither azulene nor resin. 
B. Ottoes which are yellow, containing resin only. 
C. Ottoes which are blue, containing azulene only. 
D. Ottoes which are brown-green and yellow-green, containing azulene and 
resin together, in proportions varying as optically indicated. 
It is remarkable how little azulene gives colour to an oil that contains no 
yellow resin : the otto of chamomile is familiarized to us by its blue colour, but 
it does not contain one per cent, of azulene ; Patchouly otto, which yields six 
per cent., and wormwood otto which gives three per cent, of azulene, do not 
appear at all blue, owing to the presence of an excessive quantity of yellow 
resin. 
At the third fractioning of wormwood, the yellow resin and the azulene are 
in due proportions to form a green solution, and such is probably the case with 
other ottoes known for their green colour, such as Caguput, but which I have 
not yet examined. 
Of the chemistry of azulene, and the part it plays in connection with odorous 
bodies, I hope soon to eliminate some fresh facts and to place them before the 
reader. 
ON THE EXTRACTION OF THALLIUM ON A LARGE SCALE FROM THE 
FLUE-DUST OF PYRITE BURNERS. 
BY MR. W. CROOKES. 
» 
All the processes for the extraction of thallium hitherto published by myself and 
others have been applicable to but small quantities of the material from which the 
metal is obtained. They have, in most cases, directed the employment of distilled 
water and porcelain basins, and have involved the passing of sulphuretted hydrogen 
through filtrates,—a method of proceeding altogether out of the question when large 
quantities of material are to be dealt with. Having for many months past been occupied, 
in conjunction with Messrs. Hopkin and Williams, the manufacturing chemists, of 
‘Wandsworth, on the extraction of the metal from an amount of material far greater 
than has ever been treated before, I have received from various quarters some hundreds 
of specimens of deposit, flue-dust, and minerals, every one of which was first of all care¬ 
fully tested for thallium by means of the spectroscope. The practical employment of 
spectrum analysis is, I regret to say, of but very limited use, and lias caused me many 
disappointments before I finally determined to abandon it, except by way of confirma¬ 
tion in subsequent experiments. The spectrum by itself gives no indication of quan¬ 
tity. The green line produced by the 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 I 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, 
which render the separation of the thallium in a pure state a rather difficult matter. 
Amongst these metals I have found mercury, copper, arsenic, antimony, iron, zinc, 
cadmium, lime, and sehjnium. The flue-dust upon which we have at present been ope- 
