41 



MANUFACTURE OF OXALIC ACID. 



The manufacture of oxalic acid is apparently an entirely neglected 

 industry in this country and is one which should receive consideration 

 from chemical manufacturers, and could undoubtedly be made an 

 industry of considerable value. As will be seen from the following 

 table imports are steadily increasing and have reached quite a large 

 figure : 



Quantity of oxalic acid imported, 1891-1905. 



While from the point of view of the utilization of mill wastes this 

 industry must be of minor importance for some time, there seems to 

 be an opening for several plants of sufficient capacity to supply our 

 home demand, and probably an export trade in oxalic acid could be 

 developed, just as has been done in the case of acetate of lime. The 

 rapid growth of imports during the past four years promises well for 

 the future of this industry in the United States. 



Oxalic acid is prepared from sawdust by fusing with caustic alka- 

 lies. To prepare the caustic alkali solution, potassium and sodium 

 carbonates are mixed in such proportion that after causticizing (treat- 

 ing with lime water, whereby sodium and potassium hydrates are pro- 

 duced .and calcium carbonate is precipitated) the proportion of potas- 

 sium hydroxid to sodium hydroxid shall be about 4 to 6. A mixture 

 of the two salts is dissolved in about 8 times its weight of water and 

 made caustic by boiling in an iron pan with slaked lime. After the 

 carbonate of lime has settled, the lye is drawn off into another pan 

 and concentrated to about 1.3 to 1.4 specific gravity. Sawdust, free 

 from large pieces of wood, is now mixed with the lye in such quantity 

 that there shall be two parts by weight of alkali to one part of saw- 

 dust. The whole is thoroughly mixed, after which all the liquid 

 should be taken up by the sawdust. The mass is then spread out 

 to a depth of from one-half to three-fourths inch on heating plates of 

 iron about 6 feet in diameter, with a 2-inch rim. It is stirred continu- 

 ously during the conversion to oxalate. The temperature should be 

 raised gradually, but care should be taken that it does not exceed 

 240 C., as oxalic acid is destroyed by higher temperatures. To pre- 

 vent too high heating it is best to heat the plates with hot gases 

 rather than by. direct fire, as by the aid of dampers the temperature 



[Cir. 36] 



