62t 



DRAGOON. 



DRAINAGE. 



C25 



oils, but soluble in acetic acid. Sulphuric acid chars it. Analysed by 

 Herberger, 100 parts yielded 



Fatty matter 2 ' 



Oxaiate of lime I' 60 



Phosphate of lime 3-70 



Benzoic acid 3'00 



Draconia 70-70 



According to Herberger, draconin is not an alkaloid, as Melandri 

 thought, but a sub-acid. (' Journ. de Pharm.,' xvii. p. 225.) 



Dragon's blood possesses no astringent properties, as was once sup- 

 posed to be the case, owing to kino being confounded with it. It is 

 now seldom used internally, but it is added to tooth-powders. It is 

 however employed as a colouring matter and an ingredient in 

 varnishes. 



A spurious dragon's blood is often made with colophony, olibanum, 

 turpentine, &c., coloured red with powdered Saunder's-wood. Gum 

 Senegal is also dyed red with tincture of Saunder's-wood and passed 

 for dragon's blood. The spurious is wrapped in the leaves of the Zea 

 Mais, or Indian com. 



Dragon's blood was known to the Greeks, and by them called 

 Kiwa&apis, cinnabar, a name which they also gave, as we now do, to a 

 mineral, the red bisulphuret of mercury or minium. 



DRAGOON. [CAVALRY.] 



DRAIN. An artificial channel formed in the ground for the purpose 

 of removing the surplus waters, whether they be supplied from the 

 atmosphere or from laud springs. These drains may be formed either 

 of loose stones, of pipes of ordinary brick earth or of stoneware, or of 

 masonry or brickwork, according to the nature and quantity of the 

 water to be removed, or to local conditions of economy. Drains are 

 classified under the names of sub-drains, main-drains, and outfall-drains, 

 according to the functions they may discharge in a system. 



DRAIN-TRAP. A pit formed at the entrance to a drain, for the 

 purpose of preventing the escape of the mephitic gases which are 

 frequently given off from the waters collected by a system of drainage ; 

 and also of preventing, aa much as possible, the introduction of sand, 

 drift, or other encumbering materials, into the subterranean channels. 

 The pit contains, usually, a species of hydraulic seal, which constitutes, 

 in fact, the trap, formed by means of a tongue descending below the 

 surface of the water, as in sketch a, when the trap is placed in the 



course of the drain ; or by a solid bell-covering, the lip of which dips 

 into the water in the oixlrnary bell traps, such as are used in London 

 houses for sinks, drains, rain-water-pipes, Ac. A siphon bend in the 

 course of a drain-pipe will constitute an efficient drain-trap, so far as 

 the prevention of smell only IB concerned ; but it is exposed to the 

 serious objection of being likely to become choked, if the waters should 

 transport much suspended matter. 



DRAINAGE. The removal from the ground of any waters whose 

 sojourn might be pernicious, from whatever source they may be sup- 

 plied, and the provision of an adequate discharge for those waters, 

 constitute the art of drainage, which has at all times engaged the most 

 serious attention of the hydraulic engineer. The Egyptians and the 

 Assyrians at a very early period executed some curious drainage works, 

 the remains of which still survive ; and the Etruscan predecessors of 

 the Roman civilisation practised the art with great success, as certainly 

 was proved by the extraordinary operations effected under the reign of 

 Tarquinius Prisons for the drainage of the low lands at the feet of the 

 seven hills. The Romans themselves devoted a great deal of attention 

 to this subject ; and there are in the treatises of Columella, Varro, 

 Cato, on agriculture, and in the books of Vitruvius and Pliny, many 

 remarkable passages illustrating the practice of the Romans in this 

 branch of applied sciences. In the middle ages the art of drainage 

 seems to have been lost sight of ; and it was not until about the end 

 of the 16th century that any great works of this description were 

 undertaken. At that period, the Dutch engineers commenced the 

 works for draining the lakes of the province of North Holland, which 

 now constitute the fertile polders of the Purmer, Beemster, Woermer, 

 Ac. ; and subsequently the great operation of draining the Bedford 

 Level was commenced under the guidance of Sir Cornelius Vermuyden. 

 All these works however were superficial, so to speak, and they were 

 only executed in low-lying, swampy districts ; but about the end of the 

 last century Elkington turned his attention to the removal of the 

 injurious waters of upland districts, and the art of drainage rapidly 

 assumed, in consequence of his success, the peculiar character which it 

 now bears. Messrs. Smith of Deanstone, Parkes, and Bailey Denton, 

 have ptrhapa been the persons who have contributed the most to its 

 advancement. 



From this brief sketch of the history of drainage, it will be seen that 

 t may be divided into two great branches, namely, the drainage by 



ABTS AND SCI. DIT. VOL. Ilr. 



means of open cuts, or the drainage by means of subterranean channels ; 

 and again, of late years, a distinction has been made between rural and 

 urban drainage, because the latter has been made to comprehend the 

 removal of household refuse in the form usually known as sewerage. 



Drainage by open cuts of course can only be applicable when the 

 waters to be removed do not attain a level superior to that of the 

 ground, and when there is an efficient outfall, either natural or arti- 

 ficial ; and its success depends upon the maintenance of a regular per- 

 manent discharge of the waters supplied by the collecting drains. The 

 surface of the water in these collecting drains must always be kept at 

 such a distance from the surface as to prevent any injurious action 

 upon the vegetation of the land, for it is to be observed that drainage 

 by open cuts is almost exclusively reserved for agricultural districts. 

 In the outfall drains, the water must not be allowed to stagnate, and 

 the cuts must be formed of such dimensions, and in such directions, as 

 to ensure the discharge in the smallest possible time. The rules for 

 calculating the areas and the inclinations of these drains will be found 

 under HYDRAULICS. 



In such cases as those of the polders of Holland, and of the fen 

 districts of the east of England, where the natural surface of the 

 land is beneath the mean water level of the surrounding country, it 

 was found necessary to isolate the land about to be drained, and to 

 create an artificial outfall into which the waters were raised, by arti- 

 ficial means, to a level which would allow of their subsequent dis- 

 charge. The Dutch engineers call these out-falls when they surround 

 a previously submerged district, " ring dykes;" and generally speaking, 

 they raise the drainage waters into them by means of Archimedian 

 screws, or of dash wheels, worked by windmills of a very rude and 

 primitive construction. In the drainage of the Haarlem lake, however, 

 steam power was resorted to, and the water from the submain drains is 

 led, through large cuts, to the pumps of some immense Cornish engines 

 of about 400-horse power each, to be raised by them into the ring 

 dyke, whose dimensions are not less than 125 feet in width by 10 feet 

 deep on the average. The outfall of the ring dyke of the Haarlem 

 lake is into the Spaarn, a river falling ultimately into the Zuyder Zee ; 

 and. as the Spaarn is itself frequently closed by high tides or by storms, 

 an elaborate system of stop gates, and some large steam-pumping 

 engines, working a set of dash-wheels, is provided to ensure the dis- 

 charge of the land waters during those periods. Very nearly the same 

 principles have been adopted in designing the works lately executed in 

 the fen districts .of Cambridgeshire and Lincolnshire ; but in these 

 countries it often happens that the formation of a large intercepting 

 drain (for the purpose of carrying off at once the upland waters, with- 

 out their being allowed to pass into the drainage cuts of the lower 

 level), will considerably diminish the duty required of the outfall 

 drain. Local conditions must always affect these matters of detail; 

 but the principle the removal of the largest possible quantity of 

 water by gravitation, instead of by artificial means is of universal 

 application. 



The drainage of bogs, or swamps, in mountainous districts, may 

 very often give rise to the application of other laws ; as for instance, 

 when the water, which maintains the permanent state of humidity it is 

 desired to remedy, is supplied by springs rising under considerable 

 pressure ; or when the swampiness of the locality arises from the mere 

 accumulation of water at the wet seasons of the year. The Bog of 

 Allen was an instance of the former condition, and in that case 

 the water was relieved by forming a series of artificial channels, or 

 vertical pipes, through which it rose, and poured into a new outfall 

 drain. The Chat Moss, however, was drained simply by means of open 

 cuts, so traced as to carry off the surface waters as rapidly as they fell, 

 and by a trifling improvement in the outfall. The latter operation is, 

 moreover, the principal one required to obviate the supposed incon- 

 venience from the occasional accumulation of rain waters ; and it may 

 be stated that there are many thousand acres of the best land in 

 Europe, now unproductive, which might be easily brought into culti- 

 vation by the execution of some unimportant works to lower the level 

 of the natural water courses of the districts in which these now value- 

 less tracts are situated. In the north of Spain, in Switzerland, and in 

 the island of Sardinia, there are numerous tracts which only require to 

 be thus treated. 



The works necessary for the drainage of a large morass, or fenny 

 district, are usually of such a nature as to require the intervention of 

 the legislature, or of the state ; because they involve in many instances 

 serious interference with private rights, and great changes in the hydro- 

 graphical arrangements of the whole water shed with which they are 

 connected. Perhaps Wells' history of the ' Bedford Level ' may furnish 

 some of the most valuable information upon this branch of the subject ; 

 or the series of Acts which govern the proceedings of the Commis- 

 sioners of the Fen districts of Cambridgeshire, namely, 29 Geo. II., c. 

 22; 39 & 40 Geo. III., c. 26; 50 Geo. III., c. 194; or those lately 

 passed for the regulation of the various Lands Drainage and Improve- 

 ment Companies, may be referred to as illustrating the principles of 

 legislation recently adopted in England in these matters. The reports 

 by de Prony on the amelioration of the ' Pontine Marshes;' by Tartiui, 

 on the ' Maremme Toscane ;' and by Fossombroni, on the ' Val di 

 Chiana," may be cited as illustrations of the scientific principles to be 

 applied in designing the necessary works. Dugdale's ' History of 

 Embankment and Draining/ may also be advantageously consulted, a 



