DETERMINATION OF SUGARS IN GRAIN AND CATTLE FOODS. 9 



The third proposition is refuted by treating the crucibles coming 

 from some of these determinations with nitric acid and determining 

 the copper by Low's method. 1 Calculating this copper to invert 

 sugar, the results were somewhat lower, but practically the same 

 dhTerence remained between the results by the two methods. Having 

 eliminated the other possibilities the cause of the difficulty seems to 

 narrow down to the nature of the substances extracted by the two 

 solvents. Water removes from vegetable matter together with sugars 

 many other substances, such as gums, pentosans, and some glucosids. 

 These as a rule are more soluble in water than in 50 per cent alcohol 

 and some are rather easily hydrolyzed by acids, yielding reducing 

 sugars. From the previous table it is seen that the principal increase 

 occurs in the total sugars or in the sugars after inversion, and not so 

 much so in the sugars before inversion. A new sample of this par- 

 ticular molasses feed (No. 8049, p. 7) was obtained from the manu- 

 facturer with a view to studying this point further, but the results 

 on this sample showed such slight differences by the two methods that 

 no further work was deemed necessary. In the case of molasses feeds 

 it is of extreme importance to have the sample finely ground before 

 extraction. Especially is this so when using the alcohol digestion 

 method, as the alcohol tends to hold back gummy material and this 

 might coat the larger particles of the sample and keep them from 

 being extracted. Molasses feeds are difficult to grind at the best, as 

 they cake very readily, but by first drying carefully they can be 

 finely ground. 



Having compared the results obtained by the two methods on rep- 

 resentative samples, it now remains to study the limitations of these 

 methods. 



LIMITATIONS OF THE METHODS. 

 SODIUM CAEBONATE DIGESTION METHOD. 



The purpose of the addition of sodium carbonate is to inhibit 

 enzyms. Should the material under extraction be acid in reaction, 

 then a portion or all of the sodium carbonate will be neutralized, 

 and 'the necessary amount of sodium carbonate to inhibit enzyms 

 will not be present. It was found that the acidity of one sample of 

 molasses food neutralized about 90 per ce'nt of the sodium carbonate 

 and in two others over 50 per cent was neutralized. Therefore in 

 using this method it is seen that the acidity of the material must be 

 determined and corrected by the addition of more sodium carbonate, 

 otherwise the results obtained would not be correct if the material 

 contained active enzyms. 



i U. S. Dept. Agr., Bureau of Chemistry Bui. 107, Revised, p. 241. 



