30 



BULLETIN 983, U. S. DEPARTMENT OF AGRICULTURE. 



long as decomposition does not become appreciable; but the following 

 table 39 on the decomposition of dextrose in sulphuric-acid solution 

 shows a marked decomposition above 175° C. (1 gram of dextrose 

 in 25 c. c. of sulphuric acid of various concentrations heated for 30 

 minutes at the indicated temperatures.) 



Per cent of sulphuric acid. 



Per cent of undecomposed dextrose. 



At 150° C. 



At 160° C. 



At 175° C 



At 185° C. 



0.1 _ 



100.0 

 96.1 

 94.4 



88.8 

 87.7 

 86.6 

 83.3 

 80.5 



94.4 

 92.7 

 83.3 

 80.5 

 75.0 

 72.2 

 71.0 

 38.8 



94.2 

 91.6 

 86.6 

 55.5 

 37.2 

 33.3 

 25.0 

 5.5 



88.8 



.5 



50.0 



1.0 



33.3 



1.5 



31.1 



2.0 



5.5 



2.5 



5.0 



3.0 



2.7 



5.0 



.0 







Neuman calls 175° C. the "critical point" and claims that tech- 

 nically there is no need of investigating the production of sugars at 

 higher temperatures. The results of the work at the Forest Products 

 Laboratory support this statement. 



Series II, however, shows that even though the total sugar yield 

 decreased at temperatures higher than that corresponding to 7.5 

 atmospheres, the portion of the total sugars which was fermentable 

 increased sufficiently to balance the decrease in total sugars, and 

 hence the final alcohol yield was practically the same at 7.5 and 9 

 atmospheres. As outlined before, the necessity for complete data 

 is at once apparent, and much of the value of series la and 16 would 

 be lost if the data for series II were not at hand. The increase, or 

 rather, the percentage of increase, in fermentable sugars may be 

 explained in part by the fact that there is a selective decomposition; 

 that is, the pentose or reducing substances other than the hexose 

 present are more easily decomposed at the high temperature than 

 is the dextrose. The following table of volatile-acid yields shows 

 that there was greater sugar decomposition, with consequent forma- 

 tion of formic acid, at 9 atmospheres than at 6 atmospheres. 



Cook Xo. 



Pressure 

 (atmos- 

 pheres). 



Acetic acid 

 (percent of 

 dry wood). 



Formic acid 

 (per cent of 

 dry wood). 



Ratio. 



Total acid 

 (percent of 

 dry wood). 



58 



6.0 

 9.0 

 7.5 



7.5 



2.47 

 3.53 

 2.62 

 2.36 



0.399 

 .659 

 .340 



1.450 



6. 19 : 1 



5. 36 : 1 

 7. 71 : 1 

 1.63:1 



2.869 



57 



4. 1S9 



47o 



2.960 



46 >> 



3.810 







a 10-minute cook. 

 39 Neumann, Dissertation, Dresden, 1910, p. 31. 



b 15-minute cook. 



