THE DETERMINATION OF CANE SUGAR 499 



secured by the clamp so as to obtain a film of material ; the mirror is then 

 adjusted so as to throw a beam of light through the prisms ; looking through 

 the observation telescope at K and moving the alidade E on the left of the 

 instrument, a dark shadow is seen to move over the field. The reference 

 point is the coincidence of the edge of the shadow with the intersection of 

 the cross lines in the field of vision ; the reading on the quadrant scale C 

 gives directly the refractive index of the material under examination, whence 

 can be obtained the percentage of dry matter by reference to the tables, 

 given in the Appendix. Instruments are now obtainable provided with a 

 sugar scale. 



To maintain a constant temperature, a stream of water should be allowed 

 to pass through the coil arranged in the instrument. 



The milled head L on the left of the base of the observation telescope 

 serves to correct for colour ; when not adjusted, instead of a uniform dark 

 shadow a coloured shadow appears, the dark shadow being obtained by rota- 

 tion of the milled head. 



Determination of Water. The direct determination of water is made by 

 the expulsion of the water as vapour at a temperature equal to, or above, 

 the boiling point at the pressure at which the determination is made. Insur- 

 ance that all the water has been expelled is obtained by the identity of conse- 

 cutive weighings, the last weighing being made after a further heating. 

 The accuracy of the determination depends on water being the only material 

 expelled, and is vitiated by the presence of other volatile bodies such as 

 acetic acid and even carbon dioxide, which is often found dissolved to a 

 considerable extent in molasses. 



A second source of error obtains in the decomposition of reducing sugars, 

 particularly fructose, at high temperatures.* To prevent, or at least reduce, 

 this source of error, the drying may be done under less than atmospheric 

 pressure in vacuum ovens, at a temperature of 70 C. The use of a vacuum 

 oven is also permissible to accelerate the drying with materials which do not 

 suffer decomposition at 100 C. Sugar materials towards the end of a drying 

 process become extremely viscous and part with the last traces of water 

 with difficulty. To decrease the time required, a large surface of exposure 

 is obtained by the use of absorbent agents, over which the sugar material 

 is distributed in the shape of a solution. The absorbents used are pumice 

 stone, and quartz sand, as suggested by Wiley and Broadbent, 4 and filter paper 

 crimped into a wad, as used by Josse. 5 These materials are dried before the 

 addition of the sugar material and are treated as a part of the container. 



Acceleration of the period of drying may also be obtained by drawing a 

 current of hot dry air over, or through, the material. In general, the con- 

 tainers used in water determinations are shallow aluminium dishes, listed by 

 dealers as specially applicable to milk analysis. 



A formal routine for the determination of water in cane sugar-house 

 products is described below. This routine may be modified by the individual 

 chemist in accordance with the principles discussed above. 



Sugars of Higher Grade. Weigh out about 5 grams into a dry container. 

 Keep at 100 C. for 10 hours. Weigh. Replace for one hour. Re-weigh 



* The extent of this loss was examined by the writer. A waste molasses was exposed for 10 hours to a tem- 

 perature of 100 C. A current of dry air, free from carbon dioxide, was drawn over the molasses. The volatile 

 matter given off was passed through calcium chloride to collect the water and through potash to collect the carbon 

 dioxide and volatile acids. Per 100 total loss of weight 98.7 was found as water, i.o as volatile acids and carbon 

 dioxide and 0.3 was apparently lost. With a juice 99.7 was found as water and 0.3 as carbon dioxide and volatile 

 acid. 



