control in the gluing operation, and to outline methods that have 
been found to give satisfactory results. The chief aim is to deal 
with the technic of gluing, rather than to present a technical discus- 
sion of glues. The publication has as a background a large amount 
of experimental work, from which far-reaching conclusions of 
practical importance have been deduced. Furthermore, these prin- 
ciples have been verified in large part in commercial operations. 
They are presented here as an aid in the improvement of gluing 
practice in the many plants which glue wood. 
GLUES USED IN WOODWORKING 
The adhesives most used in woodworking may be divided into five 
classes, as follows: Animal glues, liquid glues, vegetable (starch) 
glues, casein and vegetable-protein glues, and blood-albumin glues. 
There are various other adhesive substances 2 including silicate of 
soda, mucilages, pastes, rubber cements, cellulose cements, phenol- 
alclehyde compounds, asphalts, gums, and shellac, some of which are 
used to a limited extent for gluing wood ; but this bulletin deals only 
with the five main classes listed above. 
The properties and characteristics of the five principal classes of 
glue are given in Table 1. There is no one glue or Class of glues 
that is superior in all respects to all the others. Each class, because 
of its superiority in one or more particulars, may be expected to find 
preference for certain purposes. In some cases two or more glues 
may be found to meet requirements equally well. 
2 Marine glues are sometimes mistakenly thought to be wood-gluing adhesives. As a 
matter of fact they are used as water-excluding fillers between layers of wood and do not 
have the property of setting, which is required to produce a strong joint. 
