EDITORIAL. 
PROPERTIES OF GLUES. 
Report No. 66 of the United States Advisory Committee for Aero- 
nautics is devoted to the subject of glues used in aircraft manufacture, 
and, ‘as a result of a series of experimental and other investigations, 
it sums up the properties of five different types of glue as follows:— 
Animal glue, the properties of which are familiar to woodworkers, is 
used as a standard for comparing the other varieties. The higher 
grades of animal glue possess great strength and reliability, and, in 
general, glue of this type flows freely and does not stain fancy veneers. 
No other.glue is considered to be equally satisfactory for hand-spread- 
ing on irregularly-shaped objects. The chief features limiting its use 
are its high price and the fact that it is not very resistant to water. 
Casein glue is of comparatively recent introduction. Its strength is 
equal to that of medium-grade animal glues; it is used cold, and can 
be applied with a brush, but its most valuable feature is its high water- 
resisting property. On the other hand, casein glues have a tendency 
to stain thin veneers, and, in some varieties, the working life is relatively 
short. Vegetable glues have been widely used in recent years on account 
of their low cost. They are used cold, and remain in good working 
condition without decomposition for many days, but they are too viscous 
to spread by hand, and are not water resistant; they also have a tendency 
to stain. thin faney veneers. Blood albumin glue has shown high 
resistance to water, especially in the boiling test. This property makes 
it suitable for the manufacture of plywood, which is intended to be 
softened in water and moulded to shape. - It is possible to make very 
cheap blodd glue for the production of medium or low-grade articles, 
and it can also be made in the form of a dry tissue, the glueing then 
being effected in a hot press. In this form, it would appear to be 
very useful for laying fancy veneers, since the troubles due to moisture 
changes usually experienced would be avoided. The disadvantages in 
connexion with the use of blood glues are the expensive apparatus 
required, the relatively low production of the presses, and the fact that 
they are only suitable for glueing comparatively thin pieces. In 
strength, blood glues are about the same as vegetable glues, and both 
varieties are approximately the same as, or, if anything, slightly weaker 
than, medium-grade animal glues. The properties of liquid glues are, 
in general, similar to those of animal glues, and some brands give 
joints of equal strength. Their great advantage is that they are pur- 
chased in prepared form ready for immediate use, and this feature 
renders them very convenient for small jobs. Liquid glues, however, 
are expensive, and this fact, together with their poor water-resisting 
properties, tends to limit their use. Another drawback is the difficulty 
the user has of distinguishing between good and bad brands, the latter 
being very weak and unreliable. Altogether, it appears from the fore- 
going notes that none of the glues referred to is so far superior to the 
others as to be suitable for universal application. Evidently, the pro- 
perties of each variety must be considered in relation to the purpose for 
which it is to be employed. Further information as to the sources, pro- 
perties, methods of manufacture, methods of applying, and methods of 
testing the glues above referred to is given inthe report, which is 
entitled “Glues Used in Airplane Parts.” 
C.9946.—3 337 
