RETRENCHMEXT. 



RETRENCHMENT. 



46 



To prepare this acid, nitrate of potash is carefully conveyed by the 

 neck into the body of the retort, and then sulphuric acid is added to 

 it by means of the retort funnel rf, which prevents any of this acid 

 from remaining in the neck of the retort, and being washed down by 

 and contaminating the nitric acid, as it condenses and passes into the 

 receiver. In this case, when heat is applied to the retort, nitric acid 

 and water rise together in vapour from the body of the retort, and are 

 condensed in the neck ; but when the product is more difficult of 

 condensation, the neck of the retort is lengthened by placing an 

 adapter e between it and the receiver, to both of which it is secured by 

 a lute ; it being understood that the wider end slips over the aperture 

 of the retort, and the narrower one is admitted into the mouth of the 

 receiver. In many cases condensation is accelerated by the use of a 

 Liebig's condenser interposed between the retort and receiver. 



[COXDEXSEB.] 



A stoppered retort/ (fg. 4) is sometimes used instead of a plain one ; 

 these retort* are more expensive, but much more convenient than 

 common ones; for both the dry and the liquid substances to be 

 employed in the operation are passed into the body of the retort 

 through the aperture, which is afterwards secured by a stopper, 

 without having recourse to the retort funnel. Frequently also a 

 quilted or tubulated receiver is used instead of the plain one above 

 described : this is represented by g ; the tube is inserted into a bottle 

 A, and this, when ammonia or other very volatile or difficultly conden- 

 sible products are distilled, dips into water, or the receiving-bottle 

 itself is immersed in water kept cold by ice or by a freezing mixture, 

 a* when hydrocyanic acid is distilled : i is the stand which supports 

 the retort, and i is the lamp by which heat is applied to it. 



Claw retorts and receivers are made of various size*, capable of 

 containing from a few ounces to several gallons, and both flint and 

 green glass are used in their manufacture. I'sually, instead of 

 applying heat by a lamp, retorts are heat*d in a sand-bath, and some- 

 times they are subjected to the direct action of the fire ; but before 

 this they are Terr commonly protected by a coating of lute. [Lcti.] 



In general, when the application of the higher temperatures is 

 required for distillation or decomposition, earthen retorts are employed. 

 In preparing hydrofluoric acid, lead is used ; and in concentrating 

 sulphuric acid, platinum retorts are now largely employed, and would 

 be universally so, were it not for their very high ] 



In the destructive distillation of coal [G.is LIGHTING] iron retorts 

 are used, and also, on the small scale, for obtaining oxygen from the 

 peroxide of manganese, and various other chemical operations. 



.:XT. in Fortification, is a work constructed within 

 another, in order to prolong the defence of the latter by impeding or 

 preventing the formation of lodgments when the enemy has gained 

 possession of it ; or to afford protection to the defenders till they can 

 retreat with safety or obtain a capitulation. In the latter instances the 

 nterior work U called by the French engineers a reduil. 



Every principal work in permanent fortification is provided with its 

 retrenchment or redout ; and some of these, ss the redout of the 

 ravelin, and of the re entering places of arms, are constructed at the 

 same time as the work itself, while others, as the retrenchments within 

 a bastion, are generally executed but a short time before they are 



In 1 .',:;_, when If etc was besieged by Charles V., the Duke of 

 Otrise, rho commanded in the town, by constructing new ramparts 

 within the old. as fast as the latter were destroyed by the besiegers, 

 succeeded at length in compelling the emperor to raise the aiege ; 

 and at the siege of Candia (1<}6>; 1 >;>;'., the Venetians raised a ram- 

 pert from one curtain to the next in rear of the gorge of the bastion 

 St. Andrea, so that, long after that bastion was breached and taken, 

 the town continued to hold out. Such prolonged defences are now 



rare, and th,e governor of a fortress is considered as having fulfilled 

 his duty if he do not surrender till a breach has been made in the 

 rampart of the enceinte; though if the bastion were retrenched, he 

 might sustain an assault without any risk of being refused a capitula- 

 tion, or of seeing the town given up to be plundered. In the event 

 of the assailants gaining the top of the breach, the defendants would 

 be able to retreat within the entrenchment, the fire from which might 

 then be concentrated upon the enemy while confined within the com- 

 paratively narrow space between the faces of the bastion. 



The kind of retrenchment proposed by Cormontaingne for the bastion 

 of a fortress is a rampart or parapet extending across the interior of 

 the work in a right line, or rather in the form of a teuaille. [x, 

 FORTIFICATION.] Ita extremities join the faces of the bastion at 20 

 or 30 yards in front of the shoulders, by which means the flank is 

 left quite free, so that all its artillery can be employed in defence of 

 the main ditch, and there is room between the retrenchment and the 

 shoulder of the bastion for two guns, by which the interior of the 

 ravelin and the ditch of itsreduit might be defended, if necessary, even 

 after the enemy had made a lodgment in the bastion. 



As the retrenchment in this situation is liable to be enfiladed by a 

 bittery of the besiegers on the glacis before the collateral bastion, it is 

 proposed that another should be formed in rear of the gorge of the 

 bastion attacked ; and as in this case there would be sufficient room, 

 the retrenchment may be in the form of a front of fortification with n 

 revetted scarp and counterscarp. 



The ditch in front of a retrenchment, as at x in FORTIFICATION, IK 

 cut quite through the parapet of the bastion, in order to prevent the 

 enemy, after the assault at the breach, from passing along the top of 

 that parapet, and getting to the rear of the retrenchment. This 

 opening of the parapet does not, however, go lower than the level of 

 the cordon of the scarp revetment, in order to avoid diminishing the 

 height of that scarp, and thus offering a facility to the enemy, should 

 he attempt to escalade the work at that place. 



Cormontaingne proposed to retrench small bastions by constructing 

 within them cavaliers of the same form as the bastion itself, and 

 having a command of 5 or 6 feet above it. The fire from this high 

 parapet might give the work some advantages during the progress of 

 the siege ; but from its figure a cavalier appears to be less proper than 

 a retrenchment in the form of a teuaille, for the defence of the terre- 

 plein at the top of the breach. 



It is evident that full bastions like A [FORTIFICATION] must be more 

 convenient for being retrenched than those which are of the kind 

 called hollow, as B ; since less earth is wanted to raise the retrench- 

 ment to the required level, and the scarps are covered by the opposite 

 side of the ditch from the view of the enemy at the top of the breach. 

 The most simple manner of retrenching a hollow bastion would be 

 that of retaining the rampart on the interior side, where it is usually 

 10 or 12 feet high, by a wall, and cutting a deep ditch at the foot; 

 then forming a traverse across the tcrreplein of the rampart on each 

 face (at 20 or 30 yards from the salient angle of the bastion) with a 

 ditch in front. The enemy, in gaining the top of the breach, \vould 

 then find himself arrested by these obstacles, and exposed to the fire of 

 the defenders, till ladders and the support of a large body of troops 

 could be obtained. The bastions nf Ciudad Rodrigo, Bodajos, and 

 St. Sebastian were retrenched in this manner when those fortresses 

 besieged by the British and their allies during the Peninsular 



Vauban, having observed that the ravelin was sometimes abandoned 

 by the defenders previously to an -expected assault, on account of the 

 difficulty of retreating across the main ditch under a fire from batteries 

 on the glacis before the bastions, constructed, in tlic interior of that 

 work, another, which might afford the defenders protection till the coming 

 night would permit them to retire in safety. This work was at first 

 only a wall, pierced with loop-holes for musketry and covering the 

 steps at the gorge ; but when Vauban increased the size of the ravelin, 

 he made this redout, or retrenchment, to consist of a rampart and 

 parapet similar to those of the ravelin itself, as at Neuf Brisac ; and 

 Cormontaingne subsequently enlarged the work, so as to render it a 

 second ravelin, as at v [FORTIFICATION]. This spacious retrenchment 

 contributes much to the prolongation of the defence of the ravelin, 

 since it is capable of containing a large body of troops ; and each of its 

 flanks carry three guns, whose fire might be directed against the 

 counter-battery at the salient of the bastion, or might serve for the 

 defence of the breach in the face of the latter, should the enemy 

 attempt to make an assault before he has obtained possession of the 

 reduit. But to take this last, it would be necessary to breach its faces 

 either by artillery or by mining ; and the passage of its ditches would 

 be difficult under a close fire from the ramparts near the shoulders of 

 the neighbouring bastions. 



In order that the defenders might be able to retain possession of the 

 extremities of the ravelin, near the main ditch, after the salient part 

 may have been taken, retrenchments or coupures, as they are called, 

 similar to the traverses, I, t, tc., are recommended to be formed 

 across the terreplcin of the ravelin. Behind these some of the 

 defenders may retire, and keep up a firffhgaiufit the enemy's lodgment 

 near z. 



When Vauban had .'enlarged the re-entering places of anus, i 

 [BASTIOS ; FORTIFICATION], ho retrenched the interior with stockades, 



