78 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[March, 



blast, the action of the fire, the production of steam, and the speed of 

 the engine. 



The engine driver generally manages his engine and fire, in such a 

 manner, as to obtain a full supply of steam previous to his arrival at 

 the foot of the incline ; with the assistance of the variable blast, he 

 ■would naturally (having plenty of steam) enlarge the orifice of the 

 blast pipe, and thus by diminishing the resistance behind the piston, 

 would increase the power of the engine, so that although going up 

 the incline, she might still maintain sufficient speed to keep up the 

 steam, notwithstanding the enlarged orifice of the blast pipe. 



When running down an incline, the orifice of the blast pipe being 

 opened to its greatest extent, the draught will be considerably di- 

 minished, because at the same time the regulator will be partially 

 shut ; the steam may in this way be very effectually kept down, al- 

 though the incline may be many miles in length : and by contracting 

 the orifice towards the approach of the foot of the incline, steam may 

 be again obtained, without having had to expend steam from the 

 boiler, to increase the draught through the fire, thus effecting an 

 economy in the consumption of fuel. 



By good management, the engineer can therefore have full power 

 over the production of steam, so as at all times to have, a good supply, 

 and to prevent almost entirely the loss occasioned by its escape from 

 the safety valves while the engine is in motion; and taking into con- 

 sideration the frequent occasions on which advantage may be derived 

 by varying the orifice of the blast pipe, it may be inferred that it is 

 as requisite to have full command of this orifice, as it is, to be able to 

 determine the position of the regulator. The speed of the engine 

 may, moreover, be occasionally regulated with advantage, by varying 

 the orifice of the blast pipe, without altering the position of the 

 steam regulator. 



To carry out, in a practical manner, the variable contraction of this 

 orifice, it is requisite 



That the apparatus should be easily constructed and applied, and 

 not liable to get out of order ; 



That its action should be simple and effective; 



That an indicator should show the area of the orifice under which 

 the engine is working. 



Having pointed out the general advantages I propose to derive 

 from the application of a variable blast, I will now describe the ap- 

 paratus that has been employed, which will be clearly understood, 

 with the assistance of the annexed figures. 



In the construction of this variable blast, there is one point on 

 which it is proper here to make a remark, which if not attended to, 

 would materially tend to destroy the good effect to be produced. 



The annular space between the internal cone and the orifice of the 

 blast pipe, if too much contracted, diminishes the energy of the blast; 

 so that it is necessary that, at the point of greatest contraction, with 

 a view to obtain the strongest draught, the relative diameter should 

 be so calculated as to leave nearly a half of an inch of space, for 

 the passage of the steam between the internal moveable cone and the 

 edge of the blast pipe. 



I The intensity of the draught through the fire can be weakened, 

 therefore, either by enlarging or by contracting the orifice of the blast 

 pipe, beyond a certain limit. I have occasionally regulated the mo- 

 tion of an engine by the contraction of the blast pipe, leaving at the 

 same time the regulator wide open, because by contracting the orifice 

 more or less, the pressure behind the piston may be varied, and so 

 regulated as to augment or diminish the effective action of the steam 

 on the piston. The adoption of this variable blast may also be con- 

 sidered as an extra security, for by keeping the internal regulating 

 cone of the blast pipe closed, while an engine is required to remain 

 stationary, no danger could arise from the accidental opening of the 

 regulator. 



Explanation of the Figures. 

 Fig. 1. Longitudinal elevation of a Locomotive Boiler, part of the 

 smoke box being removed to show the extremity of the blast pipe. 

 The circular portion of the boiler between A and L is omitted. 



Fig. 1. 



Fig. 2. Plan of the orifice of the blast pipe, showing the regulating 

 internal cone B, with its three guide ribs 6, 6, b, 

 upon an enlarged scale ; A, smoke box ; B, regulat- 

 ing cone of the variable blast; 6, b, b, three thin 

 ribs or feathers, attached to the regulating cone B, 

 for the purpose of keeping the cone B exactly in the 

 centre of the blast pipe; C, vertical rod, to which is 



attached the reg ulating cone; D, part of the chimney; E, blast pipe; 



F, hand gear to work the cone B; K, graduated plate fixed to the 



fire box, to show the position of the cone B, and the exact area of the 



orifice of the blast pipe; L, fire box. 



London, Feb. 11M, 1843. H. H. Edwards. 



The Tomb of Napoleon. — The following details are given by one of 

 the journals resp ecting the tomb iu honour of Napoleon at the Invalides : — 

 In the lower part of the equestrian statue of the Emperor, which is to be 

 erected in the court-yard, a door will be opened to a long gallery leading 

 under the dome of the building. This gallery, paved with marble in all its 

 length, is to be divided into three sections — in the first of which will be 

 placed bronze alto-relievos, representing the military deeds of the republic of 

 the emperor. The second, which exists already, and is consecrated to the 

 interment of the governors of the Invalides, is to be enlarged, and the tombs 

 at each side will be fenced off with bronze railing. The third section will be 

 also adorned with alto-relieros in bronze, recording the most notable acts of 

 the empire not military. Under the dome will be placed the tomb of the 

 Emperor made of Corsican granite, fin it will be engraved, in letters of gold, 

 the single word — Napoleon. 



