1844.1 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



337 



which, according to its angular position, catches sooner or later the 

 brackets i i, and consequently intercepts sooner or later the communi- 

 cation of the steam passages 6 b with the steam chest and also with 

 the steam cylinder. It is therefore by varying the position of the 

 double cam that the duration of the expansion is varied. In order 

 that the lengths of introduction may be equal on each side of the 

 piston, independently of the obliquity of the cams which transmit its 

 motion, the curves of the two sides of the double cam are not alike, 

 they are made expressly for each side of the piston. When the 

 steam piston is ready to begin its stroke, the valve is at five-tenths or 

 half of its course, and can no longer continue to carry one of the 

 brackets i i, of the slide plate d d, towards the double cam c, than 

 during the latter five-tenths of the stroke, which correspond with the 

 first five-tentlis of the stroke of the steam piston. 



If then the openings of the steam passages b b are not closed at five- 

 tenths of the stroke of the piston, the steam will enter the whole time, 

 and the piston will move without expansion. It is only then in five- 

 tenths, that by means of the slide valve represented in fig. 9, that the 

 expansion can be varied. This latitude is quite enough for the greater 

 number of engines when they are required to be worked to economize 

 fuel. 



To vary the expansion during the whole course of the stroke of the 

 piston, it must be also during the whole course of the stroke of the 

 piston that the brackets i i move towards the double cam e, and con- 

 sequently the slide valve which carries them. This effect is produced 

 by the arrangement fig. S, where the expansion is made by two slide 

 valves. The slide valve A' begins its stroke at the same time as the 

 piston, by means of an eccentric placed at right angles to the eccen- 

 tric which regulates the first slide valve A, as the slide valve of fig, G. 



The arms of the double cam c are so formed as to produce equal 

 introductions on each side of the piston. The two slide plates and the 

 •two slide covers with several openings easily allow the steam to pass, 

 which can thus reach the piston at a pressure very near that of gene- 

 ration. They rapidly intercept the passage at the moment when the 

 expansion is required to begin. They allow the expansion to be varied 

 by hand or by the governor during the progress of the engine. The 

 lengths of introduction which they procure are at will equal on each 

 side of the piston, or unequal, if regard is had to the surface lost by 

 the piston rod. In fine, by means of the superimposed slide valves, 

 fig. 7, the two slide plates or the two slide covers can introduce from 

 to 19 — 20, and if more rapid closings are required than those given 

 by the circular eccentric, it is obtained by means of eccentrics with 

 bosses. 



Circular Expansion Valve. 



Messrs. Cail and Derosne exhibited a circular steam valve which 

 permits the expansion to be varied in such a manner as to regulate 

 the expenditure of steam proportionally to the resistance. The fol- 

 lowing are the details in reference to the engraving Plate XIII. 



Fig. 10, vertical section of part of the cylinder and of the circular 

 valve, a, disc of the valve to regulate the entrance of the steam into 

 the cylinder; 6, valve; c, vertical rod for turning the valve ; rf, valve 

 seat; f, valve box or case ; f, passage to top of the cylinder; g, pas- 

 sage to the bottom of cylinder; k, eduction pipe ; /, steam orifice, and 

 Ic, eduction orifice, both communicating with the passages y and g; I, 

 small axis, having on the lower part a pinion working into a toothed 

 quadrant on the t<ip of disc. 



Fig. 1 1, plan of valve box taken above A B, showing a racket wheel 

 graduated and fitted on to the top of pinion axis /. 



Fig. 12, section of valve and box taken through A B. m m, steam 

 orifices in the disc communicating with similar orifices in the seat ; o, 

 steam pipe. 



Fig. 13, view of the valve seat, p p', steam orifices communicating 

 with the passages/ and g, and the same size as m m. 



Fig. 14, horizontal section of the valve through C D ; and fig. 15, 

 through E F. 



Fig. 16, view above the valve ; and fig. 17, view below the valve. 



MNERALS. — MINERAL SUBSTANCES OTHER THAN METALS. 



Building Stones. — France has a great variety of mineral produc- 

 tions, which are variously applied in building. Sometimes it is the 

 dark and dull freestone (gres) of St. Elienne, sometimes the freestone 

 of the Vosges, employed in the rebuilding of Strasburg Cathedral, 

 which takes a deep and delicate sinking and retains its arris. This 

 doubtless influenced the elaborate style of sculpture which has been 

 employed upon it. The limestones of the secondary and tertiary 

 formations are also employed. Of the former, are those employed in 

 building Besan90R, Nancy, Luueville, Metz, Dijoo, Bourges, Poitiers 



Niort, Rochelle,Bayeux, and Caen, which latter quarries long supplied 

 England, as they do many countries. The monuments of Rouen, 

 Antwerp, &c., are of Caen stone. Chalk, which is easily worked and 

 hardens on exposure to the air, has been successfully used at Orleans, 

 Angers, Tours, Saumur, and AngoulOme. The limestones of the ter- 

 tiary formations, soft enough to be easily wrought, and yet having 

 sufficient resistance for monumental purposes, has contributed to the 

 architectural beauty of Paris, Bordeaux, and Marseilles, three of the 

 greatest cities in France. Plaster stone, or gypsum, is found abun- 

 dantly. The north of France is supplied from the Paris quarries, the 

 south mainly from the deposits of the Saone and Loire, the Puy de 

 Dome, Cote d'Or, aad the neighbourhood of Aix and Carcassone. It 

 is used for building purposes and for manure. Lime is everywhere 

 abundant; some of the argillaceous strata near the plane of separation 

 of the formations are particularly well adapted for hydraulic cements. 

 The most famous are those of Pouilly, Metz, the Nivernais, &c. Brick 

 clay is chiefly turned to account in the northern departments. 



The volcanic lava of Auvergne furnishes flagstones, the use of which 

 has,' however, been abandoned for the footpaths of Paris, on account 

 of their want of strength and homogeneity, and of their consequently 

 irregular wear. 



Granite is used for paving and for monuments. The Cherbourg 

 granite is used for curbstones and footpaths. The gray granite blocks 

 of Laber in Brittany have been employed in the pedestal of the Luxor 

 obelisk, as the porphyroid granite of Corsica has in the surbase of the 

 Vendome column. 



Although numerous marble quarries are found in France the diflS- 

 culty of carriage much restricts their use. The northern quarries of 

 Avesnes supply marbles for the fronts of shops and chimney pieces. 

 The richest and most varied are those of the Pyrenees, used in the 

 Bourse, the Chamber of Deputies, Treasury or Hotel of Finance, 

 Madeleine, the Hotel of the Quai D'Orsay, &c. 



Slates are supplied from two quarters, the quai-ries of Angers, 

 (Maine and Loire,) and those of Fumay, (Ardennes). The former, 

 worked to nearly a hundred yards in depth, supply slates of superior 

 quality, as well with regard to their uniform schistose character as 

 their fine and unchangeable texture. The value quarried annually is 

 calculated at about £80,000. 



Firestones are obtained from the Loir and Cher; millstones from 

 la Ferte-sous-Gouarre ; grindstones from the Dordogne, the Vosges, 

 and the Marne. 



Suitable pottery clays are to be found in many places, at Creil, 

 Montereau, Sarguemines, where the pottery manufacture is carried on. 

 The neighbourhood of Limoges aftbrds kaolin or porcelain earth. 



The pyritous clays of the Soissonnais supply alum, copperas, and a 

 residuum for manure. 



Bitumen mines are now in considerable demand. 

 The Paris basin has many resources. It includes among them 

 building limeslone and hard gypsum, fine and hard stone for facades, 

 millstones, slabs, flagstones, quartzose sand for glasshouses, brickclay 

 (Auteuil, Vanvres, &c.), pottery clay (Montereau, Creil), &c. 



The value of building materials wrought in France annually is esti- 

 mated approximately at £2,400,000, of this amount £1,600,000 or 

 £2,000,0000 is the regular produce of quarries in constant work. 

 These quarries are 18,000 in number, employing 70,000 men. Of 

 course the quarries most worked are those around the chief towns and 

 most populous departments. Thus at the head of the list figure the 

 department of the Seine and those around it, the Seine and Oise, 

 Seine and Marne, &c.; then the department of the Gironde, supplying 

 Bordeaux ; that of Calvados, which includes the limestones of Caen 

 and the granites of Cherbourg; the North, which supplies common 

 marbles ; the Puy de Dome, volcanic lava, &c. 



The number of mineral substances exhibited at the exposition was 

 rare, and those principally worked up for ornament. 



Marbles. — France is very rich in marbles. The Romans availed 

 themselves of this stone in their monuments at Nimes, Aix, Aries, 

 Orange, Vienne, &c. During the middle ages the quarries were aban- 

 doned, and recourse was had to Spain, Italy, and the East. Charle- 

 magne, Francis I., Henry IV., and Lewis XIV., brought into work a 

 part of the strata exploited by the Romans. In the internal decora- 

 tions of the Louvre and the Tuileries Lewis XIV. greatly availed him- 

 self of French marbles. Again neglected, these quarries have in the 

 present century resumed their operations, and more than sixty depart- 

 ments are reckoned up in which are found marbles, varied in colour 

 and beauty, and suitable for all purposes except statuary. This is 

 the only kind wanting. The French sculptors have tried indigenous 

 marbles, but have been obliged to abandon them for those of Carrara 

 and Seravezza. Some ancient statues, however, were made of French 

 marble, as the Venus of Aries, recovered from the Rhone without in- 

 jury, after a submersion gf fifteen hundred j^ears. The marble of §t. 



