332 CHYMISTRY APPLIED TO AGRICULTURE. 



The process is judged to be going on well if the liquor 

 exhibits the following symptoms. 



1. When the sirup breaks short, and the bubbles upon 

 returning into it produce a sensible sound. 



2. When a dry sound, like that produced by striking 

 silk, is returned from the surface of the sirup when it is 

 struck with a skimmer. 



3. When the bubbles of foam disappear immediately 

 upon being pressed with a spoon. The boiling is always 

 perfect when the interior surface of the boiler is found, af- 

 ter the operation is ended, to retain no trace of blackness; 



The sirup is known to be bad by the following signs : 



1. When a thick, whitish, gluey foam appears upon 

 the surface of the liquor. 



2. When the liquor swells and foams, and does not 

 subside. 



3. When the escape of puffs of acid steam announces 

 that the boiling substance is burnt. 



The evils are palliated and the boiling terminated, 



1. By removing the foam as fast as it forms. 



2. By throwing into the substance small pieces of 

 butter. 



3. By stirring the liquor with a large spatula. 



4. By mixing with it a little animal charcoal. 



5. By moderating the heat. 



To avoid a portion of these evils, I throw a flood of 

 sirup into the boiler, and remove the whitish foam that 

 arises ; I stir the sirup strongly three or four times before 

 boiling commences, and skim it each time. The scum 

 that is removed is thrown into a bucket with that which is 

 produced during all the time that the liquor is boiling ; 

 these skimmings are afterwards subjected to the lever 

 press, and the remainder washed, to obtain from it all the 

 juice contained in it. The sirup obtained by pressing up- 

 on one day, is added to the liquor that is boiled the next, 

 and the water of the leaching is thrown into the evaporat- 

 ing boiler. 



When the sirup in the drying vessel shows itself to be 

 bad, especially when it gives out puffs of sharp steam, 

 which declare the substance to be burnt, it is necessary to 

 arrest the process and to treat the sirup with an additional 

 portion of animal charcoal. In this case the liquor is di- 

 luted with water till it falls to 18° or 20" of concentra- 

 tion, (= specific gravity of 1.143 to 1.161,) and then the 



