302 on the caoutchoug. ct, 23, 
it the whole way, by a small wire, pafsed spirally around 
it. Then cover this plate directly with another coating | 
of the same caoutchouc, laid over it in the same mianner as 
before, taking special care that the plate be somewhat fhorter 
at both ends than the caoutchouc coating. When thorough- 
ly dry, let the mould be withdrawn, and you have the cy- 
linder required, the metal being so entirely coated as ta 
preserve it effectually from the acids. 
‘You will easily perceive that the use of the small slits 
in the .metal was to allow the two coatings of 
caoutchouc to touch each other in these places, so as ta 
make the whole adhere firmly together, and keep the 
tube closely encased. s 
By making holes of a sufficient size in the plate, 
wherever you want to have an opening, you will be e- 
nabled there to pierce the caoutchouc without touching 
the metal, and thus to insert other tubes either formed 
in the same manner, or of glafs, where circumstances 
admit of it. 
By the same mode, the stalk of a piston may be en- 
tirely coated; and valves of any kind formed with the 
utmost facility. 
Where a tubé is wanted still to retain its elasticity, 
without danger of collapsing, the metal case may 
be omitted, and a spiral wire ofa size suited for the oc- 
Casion, substituted in its stead. 
Where the tube is long so as that it might be dif. 
ficult to withdraw it, if it be of a considerable size, a 
mould may be made of tallow, or wax, which can be dis- 
solvéd by immersing the whole in hot water; by the 
same means may be formed irregular moulds which could 
not otherwise be withdrawn; or such moulds may be 
made of clay, which can be softened by means of water, 
and wathed out. 
