OPEN-AIR EVAPORATION. 151 
fectly uncrystallizable syrups; that slow evaporation ezther 
by an open fire or by a water-bath, gives equally bad 
results. As for exposure to the action of the air 
during concentration, M. Payen remarks that, far from 
considering it very prejudicial, the effect should be regarded 
as almost nothing; for comparative experiments made in 
vacuo, in carbonic acid gas, in nitrogen and in atmospheric 
air, gave him like results for like temperatures and times of 
evaporation. 
“Acain, it is considered as a fact fully established by the 
use of apparatus, similar to that described above in the 
manufacture of beet sugar, that saccharine juices do not 
sustain appreciable injury in concentration by exposure to 
the air; and for this we have the authority of the most 
intelligent and experienced manufacturers and chemists.” * 
The truth of the foregoing observations has been fully 
confirmed by six years’ experience in the manufacture of 
sorghum syrup in the United States. Up to a certain 
point of concentration, no prejudicial influence whatever 
is occasioned by exposure to the air or to rapid boiling. 
But when a temperature of 220° F. is reached, the danger 
of decomposition of the sngar becomes very much in- 
creased, on account of the greater density of the syrup. 
Nor can this difficulty be fully obviated by any of the usual 
methods of evaporation at the ordinary pressure of the 
atmosphere, —for if the evaporation be conducted at a 
diminished temperature, as by the use of steam at 212° F., 
or in a vessel immersed in a water-bath—all the evil con- 
sequences of the prolonged action of heat will result, and 
the sugar will be much more injured than by the action of 
a strong heat at the close of the operation. 
* McCulloh’s Report, Senate Doc. 50, p. 238. 
