33 



them should be kept very shallow, the best results being obtained from 

 a depth of 1 \ inches at the upper end and 1 inch at the lower. As the 

 impurities rise to the surface they should be skimmed off with the 

 greatest care, so that by the time the sirup reaches the lower end of 

 the pan it may be perfectly clear. When the sirup reaches a temper- 

 ature of 219 F., a or a weight of 11 pounds to the gallon, a deposit of 

 malate of lime, or "niter," will be observed, which gradually coats the 

 pan. This temperature and weight are proper for good sirup, which 

 should be dipped out and carefully strained through flannel to remove 

 the " niter.'' The flannel strainer is very efficacious, the sirup flowing 

 steadily through it and coming out perfectly clear. After ten or 



FIG. 8. Modem maple-sap evaporator. 



twelve hours' boiling, the two last sections of the evaporator will 

 become more or less coated with the ' l niter " or malate of lime. Instead 

 of scraping this off or cutting it with acids, the pan should simply be 

 turned about, so as to put the coated sections toward the cold sap and 

 the clean sections in the rear. In an hour or so the boiling sap will 

 dissolve and remove the lime, all of which will be caught in the strain- 

 ers. Particular care should be taken to see that the sirup finishes at 



a This figure is accepted in parts of Vermont, but since the proper temperature varies with 

 the altitude of the sugarhouse, each operator will have to determine by experiment what is 

 right for his situation. 



262 



