comparison with the latex of Hevea and manisoba (Man- 
thot) which coagulates rapidly when it becomes slightly 
acid. 'wo and three months old samples of mangabeira 
latex may remain liquid even when they are slightly 
acid. The strength and vulcanization properties of man- 
gabeira rubber are affected by the methods of coagulating 
the latex and handling the coagulum. It was a difficult 
task, second only to that of inducing the natives to tap 
the trees, to introduce acceptable methods for rubber 
preparation. 
The natives have long used the dried strings of rubber 
found in crude cuts on the tree for making small hard 
balls and the latex for making waterproof sheets or shoes. 
In one good native recipe for coating cotton cloth a 
tablespoon of powdered sulfur and the white of an egg 
are mixed with a large cup of water, added to a liter of 
pure latex and spread thinly over the fabric. When dry 
this is placed in the sun for a day to cure. 
The first mangabeira rubber produced tor export was 
made by heating the pure latex in a bow] over a fire, 
adding a variable amount of salt or alum, if either were 
available, and removing the mass when it had coagulated. 
A worker can do this so that all of the original water in 
the latex remains entrapped in the thick soft coagulum, 
which then has the same 20 to 83 per cent rubber con- 
tent of the original latex. The most practical method of 
preparing the rubber in Ceara is to add an equal amount 
of warm water to the latex and then a smal] amount of 
a solution of table salt. Coagulation takes place within 
half an hour. Locally made clay or wood basins are more 
satisfactory for coagulation trays than the usual kerosene 
cans, for the tannic acid in the latex does not then en- 
counter rust and consequently the blue-black ink caused 
by the rust combining with the tannin does not stain 
the rubber. 
[ 306 | 
