started the commercial production of vegetable glue for woodworking. More 
recently, still other -atents on improvements in vegetable glue have been 
issued to Tunnell, Bloede, and others. 
Sources of Cassava 
Cassava belongs to a class of woody shrubs and is related, botanically, 
to the rubber tree. It will attain a height of 12 to 16 feet. Two-year old 
plants are generally used, however, and at this time they arc/ ordinarily 6 to 
10 feet in height. The roots are tuberous, resembling a giant sweet potato, 
and it is from these roots that the starch is obtained. Cassava probably 
originated in Brazil, but it has reached its greatest production in Java; and 
it is from Java that the bulk of the present supply is received. 
The raw starch may be converted directly into an adhesive, or it may 
receive an intermediate treatment known as "processing." The bulk of the 
vegetable glue used in woodworking has been made from so-called processed 
starch. The relative amounts of the -orocessed and raw starches used at the 
present time are unknown. 
Processing 
Starch is often processed before its final conversion into glue for 
the purposes of: (l) Making it more soluble by modifying the outer wall of 
the starch grain, (2) reducing its water-absorbing quality and thus producing 
a glue of low water content, and (3) producing a uniform product. 
The processing may consist of digesting the starch in hot water 
acidified with sulphuric acid and of later neutralizing the acid, or of 
treating the starch with sodium peroxide and later neutralizing the alkali. 
The processed starch is then drained and dried. These are only two of 
several methods of processing, most of which are covered by patents or care- 
fully guarded as trade secrets. 
Preparation of the Adhes iye 
Whether the basic material is a raw starch, a processed starch, or a 
starch to which chemical ingredients have been added, the preparation of an 
adhesive ordinarily follows one of three general methods. These are treat- 
ment with (l) caustic soda and heat, (2) caustic soda alone, or (3) heat 
alone. 
If both caustic soda and heat are used, the amount of caustic is com- 
monly in the neighborhood of 3 percent (based on the weight of the dry starch), 
although it may be varied to meet special requirements. A temperature in 
the general neighborhood of 150° F. is required to convert such a mixture. 
Report No. R30 -3- 
