PROPAGATION 
the machine refilled with fresh water. 
Where rainwater is available it should 
be used to fill the incubator tank. Well 
water or spring water is apt to carry 
minerals in solution that will form scales 
on the heating parts that will impede the 
circulation of the water and reduce the 
heating efficiency of the system; reducing 
the efficiency of the heating system, by 
using mineral water, will make it neces- 
sary to use more coal-oil for each hatch 
than would have been necessary had rain- 
water always been used. Using hard or 
mineral water accounts for, in some meas- 
ure at least, the increasing difficulty of 
maintaining the proper temperature in 
hot-water machines as they grow old. 
The regulator on most machines will 
have to be adjusted, from time to time, as 
the incubation proceeds, on account of the 
increasing heat given off by the eggs. If 
it can be avoided, the incubator should 
not be opened, after the chicks commence 
to hatch, until they are all hatched out 
and dry. 
The eggs should be allowed to cool 
and air a short time each day, but they 
should be placed back in the incubator as 
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