Evaporator.--The evaporator should be of heavy four-plate tin. Galvanized iron is rougher, does not solder so well, and, worst of all, from the action of the sap the galvanizing material, in boiling, is likely to give the syrup a sort of "vanilla" flavor, foreign to the real, delicate, natural maple flavor.
After trying several sorts of pans and evapo rators for sixty years, father and son, the kind the writer now uses is the kind shown in Fig. 652. It rests on a heavy sheet-iron " arch" or fur nace, which is lined with fire-brick for the fire-box and a little back of it. The writer uses a regular brick " arch" on solid foundation, with tall brick chimney, and the fire-box lined with fire-brick. Such an arch and chimney on solid stone and grout foundation will last twenty-five years or more, and does not heat the sugar-house to discomfort on warm days as does the iron arch.
Some of the advantages of this type of evapora tor are the corrugations, the siphons, and the inter changeable rear pans, shown indistinctly in the bottom of the pan in Fig. 652. The corrugations increase the surface exposed to the heat. The bot tom of the pan is crimped by machinery, up obliquely about one and one-fourth inch, then horizontally one inch, then down one and one-fourth inch obliquely, then horizontally, and so on. This fully doubles the bottom surface exposed to the fire, and nearly but not quite doubles the boiling capacity on the prin ciple of the tubular boiler.
Siphons in an evaporator permit the operator to cut off and renew at will the flow of sap from one pan or section to the next. Fig. 657 shows the kind of siphon used. It is made of heavy tin, with a cup soldered under and one-fourth inch from the bottom of each " leg," to permit the down ward pressure of the air to hold the siphon full when it is lifted from the sap and set on any level surface, and returned to the sap later. It was found that when the siphons, even with the return cups, stood with both ends in the violently boiling sap or syrup, the air from the bubbles would sometimes rise in the siphon, gradually fill the horizontal part and stop the flow. This endangered the burning of the sap in the further pans thus cut off from the sap-flow. So a tin compartment or "cup" was sol dered firmly to the outside corner of each pan at the place of transfer. These cups connect with the sap by openings close to the bottoms of the two pans connected by each siphon. The cups rise
higher than the sap ever rises in the pans, so no to prevent overflow. The sap or the syrup in the "cups" is always calm, not boiling, and the siphon connection is perfectly secure. To fill the Eir1:011, set both legs in sap enough to cover the return cups (b and c. Fig. 657), open the small stop-cock shown at the top, and suck through the rubber tube above until the siphon is full ; then shut the stop cock and the flow begins toward the lower level. In sucking up boiling sap through the small rubber tube above the stop-cock, the mouth was sometimes burned. To overcome this, a small, oval, glass bulb (a, Fig. 657) was inserted, with a small rub ber tube above and below attached to the stop cock. When the sap rises to the bulb it may be seen, the stop-cock shut, and no injury to the mouth results.
Heater (Fig. 658).—This is a deep tubular pan, with sap all around the tubes. It is set at the chimney end of the arch and the flames must all pass through the tubes. The idea is to utilize more of the heat. But it is hard to clean, the sap must be carried by a tube to the front end of the evap orator, and altogether it gives so much trouble that it is less used now than formerly, most farmers preferring to utilize the heat by means of a longer evaporator.
Interchangeable pans.—Two of these, each with two compartments, are shown at the chimney end of the evaporator (Fig. 652). The "niter" settles and hardens on the bottom of the rear section, or, at the most, the last two sections. When it reaches the eleven-pound syrup it is held only in suspension and slowly settles on the bottom of any pan where such syrup is boiling. There it burns or hardens on, retards the boiling and, if left on too long, gives the syrup a burnt or sort of caramel flavor and color. It is hard, and is removed with chisels, which injure the pan. This takes time, and the boiling must stop. But, if the fire is slackened a little, the siphons can be removed and in a moment two men can interchange the last two pans (four sections). Then the boiling at once proceeds and the thinner, sappy syrup soon removes the sedi ment. This interchangeable feature seems to be valuable for this reason. The rear pans are not corrugated, as flat bottoms are better for syrup, which boils with less fire, and they are more easily cleaned of their hardened sediment.