j l O
LILLEY AND O S M O N D 4 . METHYLOL GROUPS
some decrease in shear strength. At a suggestion from Dr. K. W. Pepper of the Chemical Research Laboratory the period at 0% R.H. was extended to three weeks, six samples then giving the following figures :--595, 670, 584, 635, 656, 630 : average 628 lb. This showed that negligible further deterioration took place. In view of the possibility of these cements being used for sealing laminated plastic tanks or other equipment exposed to high temperatures or chemical attack, the resistanceofthe cements to boiling water, dilute aad and alkali was investigated with thc results shown in Table IV.
These figures are intetesting. In all examples there was a definite drop in the strength after a 3 hours immersion but further decrease in strength was very slow. The chemical tests were drastic for a laminated phenol-formaldehyde plastic and it is interesting to note that, after 24 hours' immersion in boiling zoo/, sulphuric acid, in two instances it was the laminated plastic itself which gave way on pulling in the tensile machine and not the joint. The great resistance of these cements to acids and alkalis is also well shown by comparing the figures : the effect of acid and alkali is no more than the effect of water.
Summary and conclusions
Our experiments have, therefore, shown a convenient method of producing a stable resorcinol-formaldehyde varnish which could be set in the cold within a reasonable length of time by the addition of paraform. The resulting cement has good shear strength, figures for cemented laminated asbestos base plastics on the I-in. overlap test being of the order of 65e740 lb. The cement has considerable resistance to b o i i water and boiling dilute acids and alkalis, though from the figures shown it is not claimed that it will resist these indefinitely.
While a slight deterioration appears to take place when the joints are subjected to very dry conditions, this deterioration is almost within experimental error, and afrer six we& samples kept under conditions of 0% relative humidity still have excellent strength.
I would like to express my thanks to the D i r e c t o r s of Ferodo
Limited for permission to publish this paper, and to Mr. F. M.
Mikschik who has carried out the greater part of the experimental work and been of the greatest assistance in the preparation of the paper for the press.