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removed in the serum by the machining of fresh coagulum has 
not yet been ascertained, but is probable. In support of this we 
have the fact that Fine Hard Para which is comparatively slow 
curing, contains all the serum constituents and should be rapidly 
curing, but the vulcanization is retarded by the smoking process. 
Dealing briefly with the factors involved in the variability 
of the first type of rubber 'in which the vulcanization is accelerated 
by the amount of some protein degradation product formed during 
the maturing of the coagulum by natural biological processes, the 
following factors accelerate rate of cure : 
(X) W moisture content up to a certain limit ; 
(2) Large amount of serum ; 
(3) Thickness of coagulum up to a certain limit, which 
affects the rate of drying ; ' 
(4) Slow drying ; • 
(5) Concentration of latex ; 
(6) Action of certain chemicals, especially the alkalis, soda 
and potash and their carbonates. 
The following factors retard the rate of vulcanization : 
(1) Low moisture content in the prepared coagulum ; 
(2) Removal of serum ; 
(3) Rapid drying ; 
(4) Thinness of coagulum which produces rapid drying and 
is also responsible foj’ the removal of serum by 
machining ; 
(5) Presence of antiseptics, especially formalin, also boracic 
acid and tannic acid ; 
(6) Certain coagulants, e.g the mineral acids especially 
hydrochloric, sulphuric and hydrofluoric acids and 
certain salts especially the alums ; 
(7) Excess of coagulant — the effect of excess of weak organic 
acids, such as acetic, formic, citric, tartaric and oxalic 
is not very marked, while excess of the mineral acids 
has a marked retarding effect; 
(8) Smoking ; 
(9) Artificial methods of drying — not Very great in the ease 
of thin crepe, which is the only type of rubber subjected 
to artificial methods of drying ; 
(10) Dilution of latex with water ; 
(11) Action of water as a solvent. 
With regard to the second factor responsible for variability in 
rate of cure the influence of various factors in retarding the rate of 
cure lias not yet been investigated, but it is probable that smoking, 
mineral acid coagulants and alum and other antiseptics and chemicals 
will retard vulcanization. 
