42 



BULLETIN 983, U. S. DEPARTMENT OF AGRICULTURE. 



He inverted 50 grams of air-dry sawdust with 150 c. c. of 0.5 per cent 

 sulphuric acid (equivalent to 1.5 per cent of sulphuric acid based on 

 air-dry wood) for one-half hour at 175° C, with 112 pounds of pressure 

 to the square inch, and duplicate experiments showed yields of 20.4 

 and 20 per cent of total sugars. The percentages of total sugars 

 fermentable and the alcohol yields were not given. In the discussion 

 of his results he gives the following: 



These experiments prove that one can ■work with small amounts of liquid "without 

 exerting a deleterious action on the yields. In fact, the yields in experiments 63 and 

 64 (the two referred to above) are higher than in former ones in which larger amounts 

 of liquids were used. At the same time, the extracts contained a greater percentage 

 of sugar •which is also favorable for fermentation. On the contrary, a small amount of 

 liquid (acid solution) is not advisable, since in another experiment •with sawdust and 

 2 parts of liquid (0.5 per cent sulphuric acid! at 175° C. a considerable evolution of 

 sulphur dioxide took place with partial cooking of the materials used. 



It must be remembered that the above experiments were made on 

 50-gram samples of wood heated in an autoclave indirectly: whereas 

 the results obtained at the Forest Products Laboratory were based 

 on 100-pound samples cooked with steam. At the laboratory there 

 was no coking in instantaneous or short-time cooks with 1 part of 

 water to 1 of wood; although, with the higher acid concentrations, 

 irrespective of the amount of water used, there was always some 

 coking — that is, a darkening of the digested wood. When Neumann 

 used sulphuric acid as the catalytic agent, he nearly always employed 

 a 0.5 per cent solution and simply varied the amount. He thereby 

 confused the effect of his ratios of water and acid to wood, since they 

 were both varied simultaneously. 



If steam was used as the heating agent, of course some further 

 dilution occurred during cooking; the more water used to begin with, 

 the greater was this dilution. In an experimental apparatus, like that 

 used at the Forest Products Laboratory, the amount of steam re- 

 quired to heat the digester was greater in proportion to the amount 

 necessary to heat the wood and acid solution than it would be in a 

 large commercial digester holding two or more cords of wood. The 

 following data from cooks Xos. 30 and 34 show in general how much 

 this dilution was: 



Cook 30, 



June 30, 1914 



Cook 34, 

 July 29, 1914. 



Water per cent . . 



H 2 S0 4 do.... 



Minutes 



Atmospheres 



Blow-ofl (condensed) pounds. . 



Digested sawdust do 



Dry wood do 



Water added do 



Excess water in digested sawdust over amount added do 



Ratio of water to wood in digested sawdust 



100. 



1.80 



0. 



7.5. 



38.48. 



271.20. 



103.55. 



103.5. 



64.10. 



1. 62 to 1. 



125. 



1.80. 



0. 



7.5. 



41.41. 



288.06. 



100.68. 



126. 



61.38. 



1.86 to 1. 



