260 FERMENTABLE [CH. XHI 



given on p. 23 gives satisfactory results, and although 

 many alternative methods may be used to confirm the 

 results it will in most cases be quite sufficient. 



It is desirable that experience should be gained in the 

 use of one method before attempting others, but when 

 results can be confirmed by the application of an in- 

 dependent method, it may sometimes be satisfactory to 

 use more than one for the same object. 



If any proteids, etc., are found in the solution after 

 precipitation of the dextrins, they should be removed by 

 mercuric chloride as in previous cases, but this will rarely 

 occur. 



Qualitative test for fermentable sug^ars. 



To a portion of solution add a small quantity of active 

 yeast suspended in pure water and allow it to stand in 

 a warm place for several hours in a flask fitted with a 

 bent tube, the free end of which passes into a solution of 

 baryta water protected from access of air. 



If fermentable sugars are present an abundant pre- 

 cipitate will be caused in the baryta-water (from COj 

 evolved), and alcohol can be detected in the contents of 

 the flask by distilling off a small portion and testing the 

 distillate by iodoform or other reactions. 



Quantitative. 



To estimate the amount of fermentable sugars it is 

 usual to absorb the CO2 evolved in some appropriate form 

 of apparatus which can be weighed before and after 

 absorption of the gas ; or to estimate the CO2 by loss of 



