FOUNDING; FOUNDRY 483 



g, side openings for receiving the tuyeres, of which there are six upon each side of 

 the furnace. Each of them may be shut at pleasure, by means of a small cast-iron 

 plate, A, made to slide horizontally in grooves sunk in the main plate, pierced with 

 the holes g g. 



k k, interior lining of the surface, made of sand, somewhat argillaceous, in the fol- 

 lowing way : After having laid at the bottom of the furnace a bed of sand a few inches 

 thick, slightly sloped towards the orifice of discharge, there is set upright, in the axis 

 of the cupola, a wooden cylinder of its whole height, and of a diameter a little less 

 than that of the vacant space belonging to the top of the furnace. Sand is to be then 

 rammed in so as to fill the whole of the furnace ; after which the wooden cylinder is 

 withdrawn, and the lining of the sand is cut or shaved away, till it has received tho 

 proper form. 



This lining lasts generally five or six weeks, when there are six meltings weekly. 



i i, cast-iron circular plate, through which the mouth of the furnace passes for 

 protecting the lining in k during the introduction of the charges. 



N N, level of the floor of the foundry. The portion of it below the running-out 

 orifice consists of sand, so that it maybe readily sunk when it is wished to receive the 

 melted metal in ladles or pots of large dimensions. 



The fan distributes the blast from the main pipe to three principal points, by three 

 branch tubes of distribution. A register, consisting of a cast-iron plate sliding with 

 friction in a frame, serves to intercept the blast at any moment, when it is not desirable 

 to stop the moving power. A large main pipe of zinc or sheet iron is fitted to the 

 orifico of the slide valve. It is square at the beginning, or only rounded at tho 

 angles ; but at a little distance it becomes cylindrical, and conducts the blast to the 

 divaricating points. There, each of the branches turns up vertically, and terminates 

 at b b, fig. 1003, where it presents a circular orifice of 7? inches. Upon each of the 

 upright pipes b, the one end of an elbow-tube of zinc c c c, fig. 1003, is adjusted 

 rather loosely, and the other end receives a tuyere of wrought iron d d, through tho 

 intervention of a shifting hose or collar of leather cod, hooped with iron wire to 

 both the tube and the tuyere. The portion c c c may be raised or lowered, by sliding 

 upon the pipe b, in order to bring the nozzle of the tuyere d d, to the requisite 

 point of the furnace. The portion c c c may be made also of wrought iron. A 

 power of 4 horses is adequate to drive this fan, for supplying blast to 3 furnaces. 



The founders have observed that the efflux of air was not the same when blown into 

 the atmosphere as it was when blown into the furnaces ; the velocity of the fan, 

 with the same impulsive power, being considerably increased in the latter case. 

 They imagine that this circumstance arises from the blast being sucked in, so to 

 speak, by the draught of the furnace, and that the fan then supplied a greater quantity 

 of air. 



The following experimental researches show the fallacy of this opinion. Two water 

 siphons, e e e,fff, made of glass tubes, one-fifth of an inch in the bore, were in- 

 serted into the tuyere, containing water in the portions g, h. The one of these 

 manometers for measuring the pressure of the air was inserted at k, the other in tho 

 centre of the nozzle. The size of this glass tube was too small to obstruct in any 

 sensible degree the outlet of the air. It was found that when the tuyeres of the fan 

 discharged into the open air, the expenditure by a nozzle of a constant diameter was 

 proportional to the number of the revolutions of the vanes. It was further found, 

 that when the speed of the vanes was constant, the expenditure by one or two nozzles 

 was proportional to the total area of these nozzles. The following formulse give tho 

 volume of air furnished by the fan, when the number of turns and the area of the 

 nozzles are known : 



' 



The volume is measured at 32 Fahr., under a pressure of 29-6 inches barom. 



$=the total area of the orifices of the tuyeres in square inches. 



n = tho number of turns of the vanes in a minute, 



After measuring the speed of the vanes blowing into the atmosphere, if we intro- 

 duce the nozzle of discharge into the orifice of the furnace, we shall find that their 

 speed immediately augments in a notable degree. We might, therefore, naturally 

 suppose that the fan furnishes more air in the second case than in the first; but a 

 little reflection win show that it is not so. In fact, the air which issues in a cold 

 state from the tuyere encounters instantly in tho furnace a very high temperature, 

 which expands it, and contributes, along with tho solid matters with which the 



