DETERMINATION OF SUGARS IN GRAIN AND CATTLE FOODS. 11 



action; the inhibiting agent having been neutralized, the enzyms 

 again become active. 



Time is an important factor in chemical analysis, as a chemist is 

 often called away from his work and the solution in consequence 

 stands for some time. It is well, therefore, to have a method that will 

 allow of such delays without seriously affecting the results. When 

 using the sodium carbonate digestion method such a lapse of time will 

 certainly introduce an error, and it is readily seen that only the results 

 which have been obtained by following very closely the procedure 

 as outlined can be relied upon. 



ALCOHOL DIGESTION METHOD. 



The limitations of the sodium carbonate do not seem to apply in 

 the case of the alcohol method. No substance need be added to the 

 alcohol to destroy or inhibit the enzyms, as the alcohol itself and 

 also the heat of extraction effects this. Hudson and Paine 1 have 

 lately found that the enzym invertase is destroyed by 50 per cent 

 alcohol. After the enzyms are killed there is little chance of the 

 extract changing on standing except through outside contamination. 

 Church and Straughn in their corn work have many times analyzed 

 a portion of the fresh alcoholic extract and then shipped the remain- 

 der of their extract to be examined later. Results in all cases have 

 been comparable, and the samples in some cases have been stored 

 for from four to eight months before analysis. The alcohol method 

 as given on page 3 indicates two or three points at which the work 

 can be stopped and as much as a day or more elapse without fear of 

 introducing any error. This is of great importance to the chemist 

 who is called upon to make other determinations at the same time 

 and who is liable to be called away from his work at any time. The 

 natural acidity of the sample in this method does not play as impor- 

 tant a part as in the other one. It is obvious, however, that if 

 digestions of strongly acid substances are to be made the material 

 should be neutralized. Again, if the alcohol used is strongly acid, 

 it also should be neutralized. 



DUPLICATING RESULTS. 



Some methods will yield duplicate results when the determina- 

 tions are carried on side by side that may not give concordant results 

 when used at another time on the same sample. This is often 

 noted when uncontrollable conditions which affect the results are 

 present, or when the details of the manipulation are not accurately 

 described in the method. When an extraction is to be made and the 

 extract analyzed, questions of temperature and length of time of 



i U. S. Dept. Agr., Bureau of Chemistry Cir. 58. U. S. Dept. Agr., Bureau of Chemistry Bui. 127. 



