CANNING SARDINES 147 
be most satisfactory. The air can also be heated by passing it over 
pipes, through which high-pressure steam, hot oil, or combustion 
gases are circulated. Of these the last probably is most satisfactory. 
Another type of heater heats the air by mixing with it the products 
of combustion from a furnace burning oil or gas. Hard coal or coke 
can also be used, but not very satisfactorily. If correctly designed 
and operated with good grade fuel, even ordinary fuel oil, this type 
of furnace gives very high fuel efficiencies, operates with negligible 
odor and smoke, and will not damage the fish. It is recommended 
that this type of furnace be used if gas at a low enough price to make 
its use feasible can not be obtained. Several companies manu- 
facture and guarantee such furnaces. They are not dangerous to 
operate and should not materially increase fire insurance rates on 
the plant in which they are located. 
In the California plants, either oil or natural gas is used for fuel, 
being cheaper than coal. In Maine, however, heat units can be 
purchased in the form of coal at about half their cost in the form of 
oil. This should be considered in planning equipment, as it may 
turn out to be advisable for this reason to heat the air by passing it 
over high-pressure steam coils or through a heat interchanger, coal 
being used as the fuel. 
Heat from the furnace is mixed with the recirculated air and blown 
through the cooker by the fan, as shown in the diagram. The 
temperature of the air in the cooker can be controlled by hand or 
automatically, whichever is more desirable. Such controls as this 
have proved very satisfactory. 
One method of handling the flakes so that they will remain in a 
virtually horizontal position throughout their passage through the 
cooker and cooler is illustrated in Figure 27. 
Details in regard to chains, sprockets, guides for the chains and 
flakes, and the best method of driving the unit should, of course, 
be handled by an engineer versed in these matters. Chain manu- 
facturers are in a position to handle such details. Two points in 
particular should be kept in mind in handling the flakes. At the 
ends of the conveyer, where the flakes change from one level to 
another, through shafting can not be used because the flakes pass 
between the sprockets. At other places, however, it can be used. 
It is particularly necessary for the two chains to run evenly, other- 
wise the flake carriers or flakes will get out of line and cause difficulty. 
Chain manufacturers can show how to make the two chains run 
evenly. ‘Take-ups’”’ for the two chains should be geared together 
so that each chain will be taken up in the same amount. 
Rollers can be placed on the flakes so that they can be conveyed 
directly on the chains. It will be much better, however, to use a 
light metal framework as a carrier upon which the flakes are placed. 
This permits light-weight, inexpensive flakes to be used. Either 
system allows the flakes to be removed as they come from the cooler. 
At times it may be desirable to remove some flakes and keep them 
on trucks for a time instead of sending them directly to the packers. 
In designing: the cooker the upper runs of flakes should be spaced 
a little farther apart than the lower ones, if the fish enter at the top. 
Should they enter at the bottom the arrangement should be reversed. 
This spacing can be made by using different sized sprockets, or 
preferably by having the line of flakes move down a slight incline, 
