332 ARTIFICIAL INCUBATION 
and spoiling the eggs. A strongly built copper tank, with proper 
care, should last many years, but a thin copper or tin tank can- 
not be expected to last longer than two or three seasons. Sedi- 
ment soon forms in the bottom of the tank, especially if hard 
water be used. The tank is hard to clean, and this sediment 
accumulates in different parts of the circuit and causes uneven radi- 
ation, with variation in the temperature of the different parts of the 
machine. Hot-water machines will hold the heat longer than the 
hot-air type; they have the advantage that when, for any reason, 
the lamp goes out in the night, there is less danger of an incubator 
cooling down to a dangerous degree before it is discovered. 
Fic. 158.—Modern mammoth incubators. A, Phantom view showing arrangement 
of pipes and circulation of water; B, another make of incubator with brooders below. (Pho- 
tos, A, Hall Mammoth Incubator Co.; B, Candee Incubator Co.) 
The hot-air incubators seem to be ihe most popular, no doubt 
because they require less attention, are cheaper, less complicated, 
and less liable to get out of repair. There are a number of excellent 
hot-water incubators on the market, but, all things considered, 
the hot-air type is the safest and best. 
Incubators, according to their size and type, are also classified 
as individual, or small, and mammoth incubators. The small 
ones are composed of single compartments for the eggs, with 
capacities of fifty to five hundred, each unit being a separate 
machine heated by its own lamp. The mammoth incubator con- 
sists of multiple units—a number of egg chambers—the entire 
machine having a capacity of from two thousand to fifteen or 
twenty thousand eggs, heat being generated in a central heating 
plant or boiler, and conveyed to all the compartments by means 
of hot-water pipes extending above the egg trays (Fig. 158). 
