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LXXI. Some Memoranda respecting Caoutchouc. By 
B. M. Forster, Esq. 
To Dr. Tilloch. 
Sir, — Sixce I mentioned to you, in my letter of 26th March, 
that I had expanded a small bottle of Caoutchouc (India-Rubber) 
by means of a condensing syringe, I have been informed of 
several instances of such bottles haying been stretched in a like 
or nearly like manner some years ago, so that what ] communi- 
cated to you as new, was not so. 
I have some notion, that in one of the periodical publications 
a few years ago, there was an account of a bottle of this sub- 
stance having been considerably enlarged by letting in coal gas, 
the bottle being attached to the end of a gas-light pipe: probably 
the caoutchouc might have been softened first. 
An ingenious artist, well known by his excellent paintings for 
magic-lantern slides, named Matthias More, has informed me 
that he has stretched bottles of caoutchouc with a common pair 
of bellows, after they were become soft by having been soaked 
for many hours in warm (not boiling) water. 
Mr. More also has stretched pieces of this substance to a very 
great length, until they became exceedingly thin and transpa- 
rent. I have seen some small pieces or leaves of it, which ap- 
peared not unlike gold-beaters’ skin, and were of a ‘beautiful- 
looking substance. With such power, Mr. More says he has made 
air-balloons the size of a common hen’s egg, which when filled 
with gas ascended. He had a plan for making long pieces of 
this substance, to use instead of glass slides for magic-lanterns, 
on which the figures were, I understand, to be printed, and after- 
wards coloured; but not succeeding in some part of the process, 
he gave up the scheme altogether. The pieces on which the 
figures were, he intended should be wound on, and off, an axis, in 
the manner that tapes for measuring are; so that, had the scheme 
succeeded, long processions might have been exhibited without 
the interruption occasioned by using several glass slides in frames, 
as usual, 
May 4, 1822. B. M. Forster. 
LXXI, On 
