39 



CHAPTER XIX 



A is a shallow receptacle of thick glass partly filled with mercury ; on 

 the upper side at B is a tubulure to be connected to the vapour space of the 

 pan by stout rubber tubing ; at C is the neck of the receptacle into which 

 fits tightly the barometer tubing D, graduated in tenths of an inch. The 

 receptacle A being filled with mercury the graduated barometer tubing is 

 then inserted in the neck of the flask and mercury is sucked up above the 

 level of the stop-cock at E, which is then closed. The mercury in A is then 

 adjusted until its level is coincident with the zero mark on D. If then con- 

 nection be made to the vapour space of a vacuum apparatus by way of B, 

 the height of the column of mercury will directly measure the pressure in the 

 pan. 



After the pressure in the pan and the temperature of the boiling mass 

 have been determined by reference to the tables, the eleva- 

 tion of the boiling point is found, and from this the apparent 

 "percentage of sugar in the boiling mass is determined. 



Instead of using tables, Claassen has devised a me- 

 chanical scale for determining the apparent percentage of 

 sugar. In Fig. 238, A, B, and C are three scales ; A and 

 C are fixed and B is a sliding scale ; A is the vacuum scale 

 and C is the temperature scale; C is graduated in equal 

 divisions corresponding to the divisions of a thermometer ; 

 on A, opposite to the temperature divisions on C, are 

 marked the corresponding pressures or vacua at which 

 water boils. The sliding scale B is graduated so as to 

 connect the elevation of the boiling point with the amount 

 of sugar present, on the same basis as the divisions in the 

 scale C. A determination is actually made as under. 



The vacuum in the pan is 28 o inches and the tempera- 

 ture is 140 F. The zero on the scale B is placed opposite 

 28 o on the scale A ; the division on the scale C corres- 

 ponding to a temperature of 140-0 F. is then noted, and 

 opposite this on the scale B is the division 89-9, i.e., the 

 boiling mass contains apparently 89-9 per cent, of sugar. 



Now a temperature of 140 F. is the boiling point of 

 a 74*2 per cent, solution of cane sugar, and hence the 

 supersaturation is 89-9/74-7, or 1-21. 



It may at once be stated that it is only bodies in solu- 

 tion that affect the boiling point, and that sugar that has 

 crystallized out has no effect at all. It is only then with 

 masses boiled string-proof that the apparent sugar percentage of the whole 

 mass is given ; in other cases it is the apparent sugar percentage of the 

 mother liquor. The scales in the brasmoscope are calculated on a sugar 

 basis, and give only the apparent percentage of total solids expressed as 

 sugar, exactly as the Brix spindle gives also apparent total solids. Actu- 

 ally the non-sugar causes weight for weight a greater elevation of the 

 boiling point than does the sugar, so that the brasmoscope indication 

 will always be higher than the true total solids, and this will be the more 

 pronounced the impurer the mass that is being tested. 



Application of Supersaturation Coefficients or Boiling Point Elevations. 

 In actual work three distinct conditions arise. These are first in the forma- 

 tion of grain, secondly in the' deposit of sugar on grain already formed, and 

 thirdly in the determination of the striking point. It is not possible to state 



FIG. 238 



