1844.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL, 



in 



some beds, being manifest in its gaseous state. Again, as I have pre- 

 viously observed, air is always present with water, and in its latent 

 state, and consequently when combustion is generated by the intrusion 

 of saline waters in fossil beds, in their primary condition, the alkalis 

 being in their uncombined state, air is liberated in sufficient quantity 

 to sustain the internal fire. It cannot for a moment be contended, 

 that spontaneous combustion will not be elicited from mixed bodies 

 buried within the earth, for the artificial volcano distinctly proves 

 that all the phenomena of volcanic action may be truly imitated. 



The earth is deriving a large and continuous supply of oxygen and 

 azote from the atmospliere, and the phenomena consequent thereon 

 are variously manifest in different regions of the earth : in the vast 

 expanse of deserts in Asia and Africa, the virgin soils greedily imbibe 

 air as well as rains and dews, the oxygen entering into combination 

 with the marine exuvis, the hydrogen uniting with the sulphur, and 

 escaping to the surface as sulphuretted hydrogen. This gas, so 

 inimical to the existence of man, is continually evolved in those parts 

 of the desert which have become covered with rank vegetation: be- 

 tieath the rainless regions the sulphureous gas is principally evolved : 

 on the other hand nitrogen readily unites with the supporters of com- 

 bustion, becomes a component of many earthy bodies, and is a proxi- 

 mate cause of the generation of nitrates. Chlorine freely evolved 

 unites with sulphur and phospliorus and forms an acid, and this acid 

 is again decomposed by the uncombined alkalis, deposited as a 

 weutral body, on or in the surface of the earth, it is the subject of 

 incessant change, separating and recombining as local influences may 

 determine. Chlorine and oxygen are the only gases which emit light 

 under any circumstances : chlorine has a most powerful attraction for 

 oxygen, decomposing water and other substances, of which hydrogen 

 is an element, when at a red heat. If chlorine be liberated from its 

 combinations in calcarious fossil beds, and is retained in its cavities, 

 the phosphorous, which abounds in these beds, uniting with it, will 

 take fire and exhibit the phenomena of spontaneous combustion ; the 

 •heat thus produced, and communicated to the sulphur and iron, or 

 other metals, or undecompounded alkaline earths, with water, the 

 &eat is strengthened and increased, and must of necessity increase, so 

 long as the causes of effects produced are in operation. In the heat 

 thus produced, the electric matter, in its latent state, is liberated, and 

 intense electric action is generated, which is followed by a sequence 

 of events favourable to the development and continuous support of 

 .combustion. 



Spontaneous combustion takes place under numerous combinations. 

 In the union of ammoniacal and muriatic acid gases, much heat is 

 evolved : mixtures of the inflammable gases with oxygen generate 

 heat: again, heat generated in the sulphates, combustion takes place: 

 the nitrates and chlorates in deflagration with metallic bodies, or with 

 sulphur, phosphorus, &c., undergo a great enlargement of volume pro- 

 ducing light and heat : nitre, sulphur, and charcoal, present similar 

 phenomena. Sulphuric acid decomposes marble with evolution of 

 great heat and falling on caustic lime the heat is increased. All the 

 materials of combustion above enumerated (except charcoal) are com- 

 mon to, and form the chief components of, virgin or fossil soils, and 

 ibeing present are capable, under favourable circumstances, of gene- 

 rating and supporting the heat of combustion. Hydrogen with caloric 

 forms gas sixteen times as light as common air; insoluble in 

 moat substances, but capable of dissolving sulphur, phosphorus, carbon, 

 .oils, &c., and thus forming different species of inflammable gas : it 

 decomposes several metallic oxides and acids with simple or known 

 radicals: its continuous decomposition and re-production within a 

 .confined medium is considered sufficient to maintain silent combustion 

 and evolution of heat for an indefinite period of time. 



the spindle E. The steam has access from the boiler to the space G G, 

 where it increases in elasticity, till pressing upon the rim H H, its 



Fig. 1. 



BOULTON, WATT & CO.',S NEW SAFETY VALVE. 



The above sketch represents a new arrangement of safety valve, 

 adopted by Messrs. Boulton, Watt & Co. for tubular boilers, when re- 

 quired to bear a load of more than 5 lb. on the square inch. 



The two objects kept in view in such cases, were— 1st. to diminish 

 the size of the lead weights put upon the valve — objectionable not 

 only on account of expense, but also of the space taken up in the 

 valve box — witliout at the same time lessening the area for the escape 

 of steam; and 2nd. to provide the means of taking off any part of 

 the weight upon the valve, at any period of the vessel's passage, 

 with the greatest facility. 



The first of these is effected by the application of the double beat 

 or Cornish valve, in which the upper part A, rests upon the se.it B 

 by the two surfaces C C, being loaded with the weights D D D, upon 



power overcomes the weight of the vaive, and the part A, rises from 

 the fixed seat B, leaving two openings for the escape of the steam at 

 the points C C. This area is much greater than in the ordinary valve, 

 while tlie part to be loaded is only the rim H H, reducing the weights 

 to about one sixth of those otherwise necessary; a, is a small stuffing 



Kg. J.l 



box which screws into the seat B, to prevent the passage of steam 

 round the spindle E. The sides of the rising part A, are made con- 

 vex, to give a greater passage for the steam when the valve is open. 



Fig. 3. 



The second object, vii., taking off one-third or two-thirds of the 

 weight when desirable, is done by the graduated spindle E, acted 

 upon by the rod and lever L and M, which are worked by a screw 

 handle on the front of the boiler, raising the upper, or two upper 

 weights, and making the load 151b., 101b., or 51b., as maybe required. 

 If the rod L, be drawn still farther, the collar e, rises to the arms d d, 

 and raises the valve and weights together when necessary to let the 

 steam escape, the engines being at rest. 



Feb. 20, 1844. 



