CANE SUGAR. 



In the later, more convenient form of tube, Fig. 250, the discs are held in 

 position by spring metal caps. The Laurent instruments use a bayonet spring 

 catch. The objection to the use of screw metal caps is the danger of producing 

 a strain in the glass discs, whereby they themselves become optically active. 



Pellet's Continuous Tube. 11 This con- 

 sists of a tube, Fig. 251, provided with a syphon 

 overflow. The solution under analysis is contained in 

 the beaker a ; on opening the spring clip b* the 

 solution already in the tube is displaced and its 

 place is taken by that flowing in from the beaker a. 

 Until all the material originally in the tube is dis- 

 placed by that entering, a reading cannot be obtained, due to the formation 

 of striae. By arranging a wire cradle connected to and alongside of the 

 trough of the polariscope, the Pellet tube can be rolled out if it is desired 

 to introduce another tube. The Pellet tube effects a great saving of time 

 when many consecutive analyses have to be performed, in fact it is hard to 

 say why every sugar laboratory does not use this device. 



FIG. 248. 



FIG. 249. 



Water Jacketed Tube. In the Clerget analysis, where the control 

 of the temperature is of importance, the tube shown in Fig. 252 is convenient ; 

 it is filled through the aperture in the middle after both of the end caps have 

 been placed in position ; a thermometer is inserted through the same aperture 

 to take the temperature of the solution. A continuous current of water may, 

 if necessary, be made to flow through the jacket, and readings at an elevated 

 temperature obtained. 



FIG. 250. 



Value of Scale Degree. In polariscopes the scale is divided 

 into 100 equal parts on the assumption that the rotation of cane sugar 

 is independent of concentration. The following table gives the value of each 

 degree of the polariscope scale calculated from the Schmitz determinations of 

 the rotation of cane sugar at varying concentration, and in refined analyses 



*This clip is more conveniently placed on the delivery tube and resting on the table. 



442 



