USEFUL PROJECTS. 



S49 



or by any other convenient mode, 

 into the several apartments to be 

 warmed. When the rooms are at 

 too great a distance from the boiler 

 to be warmed by single pipes, then, 

 in order to prolong t)ie direction of 

 the heat, I either inclose the pipes, 

 through which the warm air is 

 conveyed, in larcjer pipes, to which 

 the steam rises from the boiler, or 

 I introduce the warm air into the 

 larger, and the steam into the small- 

 er, pipes ; by which means the air- 

 pipes are prevented from grov/ing 

 cool so soon as they would do if 

 they were exposed to the action of 

 the open air. I also in certain cases, 

 ■where I judge it proper and more 

 convenient, place my air-vessel or 

 worm in a vessel distinct from the 

 boiler, but still having a conimunica- 

 tion therewith for the steam from 

 the boiler to pass, and thus heat the 

 air vessel or worm by means of 

 steam only ; by the above process 

 too great a degree of heat is avoid- 

 ed, and the air remains unburnt, 

 and fit for respiration. In witness 

 whereof, &:c. 



On the method of making inslrume?its 



of elastic gum, with this bottles that 

 are lr6ughtfrom Brazil, by M. 

 Grossart (ChirlyJ. From the An- 

 nales de Ckimie. 



CAOUTCHOUC, or elastic 

 gum, is a subjtance v.hich has 

 engaged the attention of philoso- 

 phers ever sincp it has been known. 

 Its singular elasticity, its flexibility, 

 and the little action most substance^ 

 have upon it, have caused it to be 

 considered as very valuable for 

 many purposes, particularly in the 

 art of surgery. But it has hitherto 

 been impossible to procure instru- 



ments of this sttbstance, inasmuclx 

 as almost the whole quantity of ca- 

 outchoucbronghtinto Europecomes 

 from Brazil already fashioned into 

 bottles, birds, or other figures ; this 

 has rendered its use extremely cir- 

 cumscribed. 



It is known that these are made, 

 in that country, by means of moulds, 

 with the juice of a tree of the or? 

 der of Euphorbise. The liquid is 

 drawn from the tree by incision, 

 and it thickens in the manner of 

 resinous juices. , It would be easj^ 

 could we procure it in its original 

 state of fluidity, to give it all the 

 forms under which it might be use- 

 ful to us ; but the communications 

 \w\l\\ Brazil are very difficult for the 

 greatest part of Europe ; and the 

 necessit)' of passing Llie line, in 

 bringing it to our parts, is another 

 obstacle to the juice arriving in a 

 proper state for our purposes j as it 

 is decomposed by heat in the same 

 manner as milk, exhaling at that 

 time an extremely fetid odour, and 

 having no longer its original pro- 

 perties. Sir Joseph Banks, president 

 of the royal society of London, so 

 well-known by the voyage round 

 the world, v.-hich his attachment to 

 the sciences prompted him to un- 

 dertake, told ine he had a bottle 

 of it in its original state, but v^hich 

 after a little time became decom- 

 posed ; since which he had not been 

 able to procure any more from Lis- 

 bon, although he had offered even 

 to the value of fifty guineas for a 

 second bottle. 



Most of the persons to whom the 

 liquid has been sent, whether fronn ' 

 Cayenne, or from the isle of France 

 (where the tree that furnishes this 

 liquor is also known,) have never 

 received it but in a decomposed 

 state. I had for some time about a 



pint 



