Sample.Amount of Copper Salt.Weight of Rubber.
When Dry.After
Interval
of Four
Weeks.		Further
Interval
of Seven
Weeks.		Further
Interval
of Three
Weeks.		Percentage
in Increase
in Weight.
Grms.Grms.Grms.Grms.
10·02 grms. copper sulphate,
per 100 c.c. latex		43044148248813·5
2Ditto42843948148613·55
30·01 grms. copper sulphate,
per 100 c.c. latex		}962987103510367·7
0·01 grms. copper acetate,
per 100 c.c. latex
40·025 grms. copper sulphate,
per 100 c.c. latex		50251355856011·5

In view of the effect thus produced by the addition of traces to latex of a copper salt, and the observed effect on rubber of contact with copper salts, one may imagine the result produced some years ago when on an estate smoked sheets were washed with a solution of copper sulphate as a remedy for surface moulds!

With the exception of this chemical action we know of no other means by which tackiness is produced, beyond those of direct sunshine and heat. Cases governed by these two causes are common on estates. They are confined chiefly to the lowest grades of scrap rubber, when the component raw materials have been exposed to the sun for a period before being brought to the factory.

It is now comparatively rare to find cases of tackiness in the higher grades of crepe, and when they occur, one may look for evidence of gross carelessness in the admission of direct sunshine. Usually this means the failure of some individual to regulate window shutters according to the position of the sun in the sky. More rarely does it happen that tackiness may have been induced by placing thin crepe rubber too near the iron roof of the drying-shed.

Regarding the question as to whether tackiness may be communicated by direct contact, opinion appears to be divided. It has been stated that sound rubber left in contact with tacky specimens was found to be unaffected after two years. On the other hand, it is claimed that tackiness has been induced in a sound rubber by infecting it with small pieces which were tacky. In a preliminary article on the effect of copper and copper salts upon pieces of dried and sound crepe[21] it was noted, after one year, that tackiness had been communicated from the treated portion to the “blank” in contact. There is sufficient evidence to warrant the injunction that tacky rubber should be excluded from contact with sound rubber. If shipped it should be packed separately.

[21] Report I., 1916 (Sidney Morgan), Rubber Growers’ Association (Malaya).

Compounds have been put upon the market which assumedly claim to be cures for tackiness. These are merely palliatives, consisting of starch, talc, or chalk powders, which counteract stickiness.

No Cure for Tackiness.—At the present stage of our knowledge, there appears to be no cure for tackiness. Neither do we see the necessity for a cure when the phenomenon may be avoided by taking simple precautions, which may be briefly summarised thus:

(1) Any permanent openings through which it is possible for direct sunlight to enter, whether large or small, should either be totally closed or provided with some substance which cuts off the direct effect of the sunlight—e.g., ruby glass or ruby glazed cloth.

(2) Rubber should under no circumstances be placed near any source of heat.