162 History of Mechanical Inventions^ and 



the interior is filled with atmospheric air, mixed to a certain extent with 

 coal gas ; the latter is increased by the distillatory action of the fire, until 

 the proportion is attained which is explosive ; it takes fire, producing the 

 rush of flame which would be followed by a sudden vacuum in the tube, ' 

 while the other side pressed by the steam gives way to this sudden im- 

 pulse, and is destroyed by a force very much smaller than would be re- 

 quired if uniformly excited." 



What Mr Taylor says may be very possible, with the exception of the 

 formation of a vacuum. Motion only obtains when the resistance is infe- 

 rior to the force applied, and ceases, except under particular circumstan-* 

 ces, as soon as the two forces become equal. This then is the case in the 

 phenomenon before us. The explosion may occasion a rush of air out- 

 wards through the fire-door, because the elastic force of the fluids within 

 the tube exceeds that of the atmosphere, but as soon as that within has so 

 expanded as to be reduced in elasticity equal to the pressure of the atmo- 

 sphere, no farther emission of air from within the boiler can possibly ensue. 

 Again, supposing the possibility of a diminution in volume of the gaseous 

 matter Avithin the boiler, the fire-door (say l4 feet wide and 24 feet long) 

 in such boilers would afford an aperture quite sufficient to supply (at the 

 moment of the diminution of volume) the void. Hence then it is evi-' 

 dent, that no force at all varying from the atmospheric pressure, can, un-"- 

 der any circumstances, be exerted on the part of the boiler exposed to the' 

 fire. 



Mr Kenwood is of opinion that hydrogen is not generated by the decom- 

 position of water from leaks in the boiler. He conceives that the sudden- 

 bursts of flame from the chimneys of steam engines arise from gusts of 

 air carrying the flame farther up the flue at some times than at others. 



Those who take an Interest in this very important discussion will find 

 another paper in the Phil, Magazine, signed an Engineer, in which the 

 author endeavours to show that the explosion of steam boilers is almost 

 always owing to neglect, or to the originally bad construction of the boil- 

 ers. Another correspondent, Mr J. Moore of Bristol states, that steam 

 engines have often exploded on their being stopped, and he is of opinion 

 that this arises from an additional strain on the boiler from within, occa- 

 sioned by the steam which previously had a free passage being prevented 

 from escaping anywhere but at the safety valve ; the aperture of which, 

 compared with the contents of the cyhnder into which the steam passed 

 before, is very small. Mr Moore suggests the application of a large valve 

 on the tube adjacent to the part where the steam is prevented from passing 

 to the engine. 



13. Account of the Collection and Preparation of the Fucua saccharinus, 

 a sea-weed J for the Chinese market, and its uses. 



This vegetable, by the Malays termed Agar-Agar, and botanically Fuctis 

 saccharinusy abounds on the coral shoals in the vicinity of Singapore, and 

 forms a bulky article of native import and export for the Chinese market, 

 a very small portion only being reserved tor the consumption of the settle- 

 ment. 



