27-2 



The Carhohydrates of the Mdngold Leaf 



constant temperature by the thermo-regulator, is circulated through 

 the jacket of the polariineter tube and bacl: to the bath by means of 

 the small centrifugal pump C; it takes only about 5 minutes to bring 

 the temperature of the tube exactly to 20-0°. 



The polarimeter \vc have used is one of Schmidt and Hacnsch's 

 Lippich iustruuieuts, with a triple field, capable of taking a -lUO mm. 

 tube and reading in angular degrees to 0-01° ; it is fitted with a spectro- 

 scopic attachment and a scale enabling the instrument to be used with 

 mono-chromatic light of any desired wave-length. All the observations 



Tit! 



Thcnnostiit for polarimetric mcasureracnts. 



recorded in the present paper were made with a sodium lamp, but for 

 this class of work a mercury vapour lamp is preferable as it obviates the 

 need of constantly replenishing the flame, gives a far brighter light and 

 is much cleaner in use. We have used very successfully a Lummer- 

 Straubel fihss lamp, fitted with a water cooling jacket, which is preferable 

 to the (|uartz mercury vapour lamps as it gives no trouble with ultra- 

 violet rays, is far cheaper and throws a small concentrated light directly 

 into the polarimcter tube. This lamp needs 2.5 volts, but can be run 

 from an ordinary !(>() volt circuit by interposing a suitable resistance; 

 for this imrpose we have used a wall type adjustable resistance with a 

 radial switch controlling twelve contacts giving a range of 2-10 amps. 



