56 



BULLETIN 983, U. S. DEPARTMENT OF AGRICULTURE. 



Three cooks were made with the use of phosphoric acid (H 3 P0 4 ) 

 alone or in mixture with sulphiric acid, and the results were as follows : 



Spruce. 

 7.5 atmospheres; 125 per cent H2O. 





Catalyst. 



Total 



Per cent of 



Alcohol yields. 



Cook No. 



(per cent 

 of original 

 dry wood.) 



total sugars 

 ferment- 

 able. 



Per cent of 



original 

 dry wood. 



Gallons 

 per ton. 



100 



1.8 per cent of sulphuric acid, 0.1 per 



cent of phosphoric acid. 

 0.9 per cent of H2SO4, 0.9 per cent of 



H3PO4. 



21.12 

 20.83 

 19. 33 



64.32 

 55.20 



51.58 



7.726 

 5.635 

 5.180 



23.24 



101 



19.62 



102 



15.69 









The above results are even better than were to be expected, if the 

 relative degrees of dissociation of the two acids are considered. The 

 slight increase in yield of cook No. 100, containing 0.1 per cent of 

 phosphoric acid in addition to 1.8 per cent of sulphuric acid, as com- 

 pared with cook No. 34 (p. 55), containing 1.8 per cent of sulphuric 

 acid only, is not sufficient when its cost is considered to warrant the 

 commercial use of even small quantities of phosphoric acid. Phos- 

 phates, of course, are necessary for yeast growth; and if they are pres- 

 ent in considerable quantities in the mash during fermentation they 

 act as a yeast stimulant. It has not been found necessary, however, 

 to add any great quantity of phosphates in order to secure satisfactory 

 fermentation. A pound or two of ammonium phosphate or a pint 

 of "sirupy" acid added to the starting yeast in the early stages of its 

 propagation is sufficient to insure vigorous growth. 



STUDY OF DIFFERENT SPECIES. 



All the cooks in this series were made under the following condi- 

 tions: 2.5 per cent of sulphuric acid; 125 per cent of water; 7.5 at- 

 mospheres of pressure; 20 minutes cooking period. The results ob- 

 tained divide the different species into their natural botanical classi- 

 fications, namely, the coniferous and broad-leaved species. Although 

 not all species in each class were tested, authentic samples of enough 

 species were used to demonstrate the value of most of those woods 

 that are commonly available for this process. 



