512 NOTES OF A BOTANIST chap, xiv 
It is found that the addition of alum hastens the 
coagulation of the milk, while ammonia has a 
contrary effect and is accordingly useful when the 
milk is required to be kept some time in a liquid 
state. 
[At the time Spruce wrote the preceding notes 
the industrial use of rubber had just commenced 
that remarkable development which has continued 
to the present time. The increased demand from 
America in 1853, which Spruce referred to, was due 
to its more extensive use for waterproof clothing, 
goloshes, etc., but still more to the extension of its 
application to many of the arts, and to its great 
value in making water-tight and air-tight tubes, 
belts and washers for machinery. But the greatest 
increase in its use has been for the tyres of bicycles, 
first solid, then about 1888 pneumatic, which latter 
soon became universal both for cycles and motor- 
carriages, and has led to an enormous consumption 
of this remarkable natural product. A short rdsu7nS 
of the present state of the rubber-trade in Para and 
the Amazon valley may be interesting to our 
readers. 
At the time Spruce and myself were in Para, 
what was called bottle -rubber was the common 
form in which it was made. This was done by 
means of a ball of clay 3 or 4 inches in diameter, 
which by means of a stick was dipped in the milky 
sap and dried in successive coats till about an inch 
thick, when the clay was extracted, leaving a 
hollow ball of rubber with a short neck. The 
smoking was done by means of a fire of the fruits 
of two kinds of palms, generally abundant in the 
rubber forests, and whose thick and acrid vapour 
