These conditions gave him a yield of alcohol equal to about 6 per 
cent of the dry weight of sawdust used, although few fermentation 
experiments were made. 
As was shown later by Neumann/ 1 Simonsen's work is contra- 
dictory in some respects, because of the fact that only a single ex- 
periment was made under each set of conditions. In his work on a 
large scale, 12 he was generally unable to duplicate the results ob- 
tained in the small autoclave cooks. The yields of alcohol varied 
considerably, although under the most favorable conditions and 
in a few exceptional cases he obtained yields which were slightly 
higher than those secured on the small scale. Simonsen's process 
was patented July 12, 1898. 13 Korner 14 later substantiated Simon- 
sen's yield of 6 per cent and showed further that the yield. of alcohol 
and sugar was in proportion to the cellulose content of the sawdust, 
straw, and sulphite cellulose used as raw material. 
A. C. Classen developed a new process in which sulphur dioxide 
was the inverting agent, although his first patent 15 covered a mix- 
ture of sawdust and concentrated sulphuric acid (50° to 60° B.) in 
which the mixture was subjected to great pressure in a hydraulic 
press. In the original Classen process 16 an aqueous solution of sul- 
phurous acid was used, though later Classen obtained three patents 17 
in which chlorine, air, or oxygen were used as the oxidizing agents 
to convert the sulphurous acid to sulphuric acid. Still later he 
obtained a patent 18 covering the process of treating the wood with 
sulphuric anhydride, and an additional patent 19 covering the process 
of heating this mixture to 123° to 135° C. 
He also patented 20 the use of a smaller amount of a more concen- 
trated solution of sulphurous acid, claiming that the acid recovery 
was more efficient when the sawdust in the digester was only slightly 
moist. In 1914 he patented 21 the use of platinum, ferric oxide, etc., 
as catalytic agents to convert the sulphurous acid into sulphuric 
acid in the digester. 
The French rights to the Classen process were sold to a M. Tafhn, 
who had experimented for several months at Tolques before the 
purchase. After satisfying himself that the process was practical, 
he organized in August, 1904, the Compagnie Industrielle des Alcools 
11 Neumann, Dissertation, Dresden, 1910. 
i 2 Zeit. fur ang. Chemie, 1898, 962. 
13 United States Patent No. 607091. It was also patented in Norway, Austria, England, France, Canada, 
Hungary, and Germany. 
" Zeit. fur ang. Chemie, 1908, 2353. 
is German Patent No. 111868. 
is German Patent No. 118540. 
17 German patents Nos. 118542, 118543, and 118544. 
is German Patent No. 121869. 
is German Patent No. 123911. 
3° German Patent No. 130980. 
si United States Patent No. 1101051. 
