282 
KNAPP'S CHEMICAL TECHNOLOaY. 
Fig. 94. 
^' The concentrating apparatus in which this separation [of 
water] is effected, consists of leaden pans and a platinum re- 
tort. The former, fig. 94, are erected over a fire, A, and sup- 
ported by iron plates, a a, against which the flame beats ; 
d d are incisions, through which the lower pans are filled. 
The evaporation precipitates a little sulphate of lead and 
oxide of iron, (anhydrous,) v/hilst the boiling point of the fluid 
attains a iieight at 65 per cent, of hydrate which endangers 
the pans, from the great heat, and causes a useless loss of 
acid by evaporation. When, therefore, about 11 per cent, 
of water has been evaporated, with which nitric oxide, 
nitric and sulphurous acids pass off, the acid is conveyed 
(having a specific gravity of 1.7) through the syphon x into 
the platinum retort, fig. 95, the fire under which is closely 
approximated to the fire of the pans A. The syphon a?, 
which is here represented as closed, is worked without a 
stop-cock by the vessel c, on filling the retort in a remark- 
ably simple and ingenious manner. When this vessel is 
lowered with its spout to the gutter d^ the outer limb of the 
syphon, which is constantly full, becomes lengthened below 
n, and acid consequently flows out. 
" The danger and great loss by breakage attending the use 
of glass vessels, have induced the manufacturers very gene- 
rally — notwithstanding the great cost — to make use of 
platinum retorts. These are made (nearly all in Paris) to 
contain from five to twenty cwts., and cost from 8,000 to 
