In the specification of the patent applied for on the list of July 1877 he showed a sketch of an instrument which consisted of a diaphragm, with a small platinum patch in the centre for an electrode, against which a hard point, made of plumbago powder cemented together with india-rubber and vulcanized, was pressed by a long spring, the pressure of the carbon against the platinum disk being adjusted by a straining screw near the base of the spring.
Most articles made of cut sheet rubber would, however, be of very limited utility were they not hardened or vulcanized by the action of sulphur or some compound of that element.
If, however, it be now subjected for an hour or so to a temperature of 140° C., a combination occurs, and vulcanized caoutchouc is the result.
Which they retain; and hollow articles, such as playing balls or injection bottles, are vulcanized in iron or brass moulds, tinned inside and very slightly greased.
The articles are first fashioned by joining the soft material; they are then varnished, and afterwards cured in ovens heated to about 135° C. The fine vulcanized " spread sheets " are made by spreading layers of indiarubber solution, already charged with the requisite proportion of sulphur, on a textile base previously prepared with a mixture of paste, glue and treacle.
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