94 BULLETIN 1370, U. S. DEPARTMENT OF AGRICULTURE 
Three by 4-inch dampers in the chimney regulate the draft. — 
Enough air to give good combustion of fuel should be admitted. | 
With proper draft the flames should extend slightly beyond the © 
arch of the chimney. | : 
The pan is set on a single line of bricks, which are laid lengthwise © 
on a 2-thickness brick wall, fiush with the inside surface of the wall. | 
A good joimt between the furnace and evaporator is conveniently © 
made with clay or mortar. With the width of furnace given in Figure6, © 
about an inch of the width of the pan on each side projects over the | 
outside of this line of brick, which protects the sides of the pan from | 
the fire. The front of the pan should be within 6 inches of the front | 
of the furnace. <A space of 1 foot between the front of the chimney | 
and the back of the pan is convenient in skimming and drawing off | 
the sirup. A small crack left here admits air to the chimney end of | 
the furnace, the draft thus created preventing too close contact of 
the flame with the sirup end of the pan. The front, or juice end, of | 
the pan should be about an inch lower than the back, or sirup end. | 
The foregoing description applies primarily to furnaces burning | 
wood. Whenever wood is more expensive than oil (p. 57), a furnace | 
of somewhat similar design may be equipped to burn oil very effi- — 
ciently. Since steam is not ordinarily available for small-scale | 
sirup manufacture, however, it is impossible to atomize the oil by use | 
of steam, as is customary in large-scale operations. Nor is it prac- | 
ticable to utilize the heat of the furnace for preheating the fuel. | 
For these reasons a mechanical oil burner must be used, and it is not J 
feasible to burn oils of such high viscosity as to require heating before } 
atomization. Fuel oils lighter than 18° Baumé, or. of such viscosity | 
that they will flow readily without heating, are usually required in | 
small installations. All mechanical oil burners need power for atom- | 
izing the fuel and injecting the proper quantity of air. The oil may | 
be pumped, but it is usually under gravity feed. The air pressure is | 
supplied by a power-driven blower or an air compressor. If elec- | 
tricity is available, a small motor is an ideal source of power for | 
operating a blower or compressor; otherwise, the power required | 
may be obtained by a belt connection to a small gasoline engine | 
(one-half horsepower) or to the shaft of the mill. Manufacturers | 
will supply information on equipment for burning fuel oil on a small | 
scale. The fuel requirement for a 12-foot evaporator (p. 23) is esti- | 
mated to be approximately 15 gallons of oil (on 12° Baumé basis, | 
p. 56) per hour, assuming a production of 16 to 17 gallons of sirup J 
per hour. = 
OPERATION 
The evaporator must be thoroughly clean when operation is started. } 
If sediment from the previous operation has been deposited on the § 
bottom and sides, a copper evaporator may be cleaned by allowing a |f 
hot dilute solution of hydrochloric (muriatic) acid to stand in it for } 
a short period. This partiaily dissolves the sediment, so that it can } 
be removed by slight serubbing while running water through the | 
pan. Galvanized iron is badly. corroded by contact with acid. | 
Evaporators may be cleaned also by boiling water in them and scrub- | 
bing, but this is time consuming. The evaporator should be cleaned § 
every two or three days, depending largely upon the quantity of § 
deposit adhering to it. When two evaporators are in use, it is con- §f 
venient to clean one every day and use the other for evaporating the | 
first supply of juice in the morning. 
