Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/380

364 found to occur in its passage through the mine. The original water lost much of its free carbonic acid gas ; its carbonates were converted into sulphates ; and it con tained now the metals iron, manganese, cobalt, and alum inium, all as sulphates, hardly a trace of any of these metals being present in the uninjured water. And matters in suspension were found to be both more abundant and more injurious than matters in solution. They consisted chiefly of copper pyrites and iron pyrites, in a very fine state of division. According to their degree of fineness the pyritic particles which escape from the settling pits at the mines travel varying distances down the stream, and may .even be detected several miles below, both in the mud of the bed of the stream and on the leaves of grass and other occasionally immersed plants. Oxidation of the pyrites into the sulphates of copper and iron w T as proved to occur all through the course of the stream, these salts, with their concomitant free sulphuric acid, producing a most injurious effect on vegetable growth. The presence of this acid in the free state has been detected in the waste water from a Welsh lead mine, in sufficient abundance to kill instantly, on several occasions, many salmon in the river into which it was discharged. The evil done by some of the most deleterious materials in mine-waters can be arrested by the interposition of conduits filled with chalk or limestone, which act as chemical filters. The carbonate of lime neutralizes the free sulphuric acid and stops the heavy metals by converting them from soluble sulphates .into insoluble carbonates. Among the most injurious sorts of refuse which can find their way into streams used for irrigating meadows are the chemical wastes from mills and factories in which the processes of dyeing, paper making, metal working, <fec , are carried on. In the majority of such cases the fatal effects on vegetation are obvious, and the rivers polluted in this way, even if their volume of pure water be very large, cannot be used at all for irrigation. The Seeds for Water-Meadows. Of the few leguminous plants which are in any degree suitable for water-meadows, Lotus corniculatus major, Trifolium hybridum, and T. pratense are those which generally flourish best : T. repens ,is less successful. Amongst grasses the highest place must "be assigned to ryegrass, especially to the Italian variety, commonly called Lolium italicum. The mixture of seeds for sowing a water-meadow demands much consideration, and must be modified according to local circumstances of soil, aspect, climate, and drainage. From the peculiar use which is made of the produce of an irrigated meadow, and from the conditions to which it is subjected, it is" necessary to include in our mixture of seeds some that produce an early crop, some that give an abundant growth, .and some that impart sweetness and good flavour, while all the kinds sown must be capable of flourishing on .irrigated soil. The following mixtures of seeds (stated in pounds per acre) have been recommended for sowing on water-meadows, Messrs Sutton of Reading, after considerable experience, (regarding No. I. as the more suitable : i. ii. Lolium perenne 8 12 Lolium italicum 8 Poa trivial is 6 3 f lyccria flu-Han v 6 2 Glycerin aquatica 4 1 Agrostisalba 1 Ai/rostis stolon if era 6 2 Alopccurus pratcnsis 2 Fcstuca datior ... ..3 2 I IT. Fcstuca 2iratcnsis 2 Fcstuca loliacca 3 2 Anthoxanthumodoratum 1 Pkleum pratense 4 2 Pludaris arundinacca... 3 2 Lotus corniculrtfns major 3 2 Trif olium hybridum. ... 1 Trifolium pratense 1 Changes in Irrigated Herbage. In irrigated meadows, though in a less degree than on sewaged land, the reduc tion of the amount or even the actual suppression of certain species of plants is occasionally well-marked. Sometimes this action is exerted upon the finer grasses, but happily also upon some of the less profitable constituents of the miscellaneous herbage. Thus Ranunculus lulbosus has been observed to become quite rare after a few years watering of a meadow in which it had been most abundant, R. acris rather increasing by the same treatment ; Plantago media was extinguished and P. lanceolata reduced 70 per cent. Amongst the grasses which may be spared, Aim cxspitosa, Briza media, and Cynosurus cristatus are gene rally much reduced by irrigation. Useful grasses which are increased are Lolium perenne and Alopecurus pratensu, and among those of less value A vena favescens, Dactylix glomerata, and Poa protends. Methods of Irrigation. There are four ways of irrigating land with water practised in England :- (1) bedwork irri gation, which is the most efficient although it is also the most costly method by which currents of water can be applied to level land ; (2) catchwork irrigation, in which the same water is caught and used repeatedly; (3) subter raneous or rather upward irrigation, in which the water in the drains is sent upwards through the soil towards the surface ; and (4) warping, in which the water is allowed to stand over a level field until it has deposited the mud suspended in it. There are two things to be attended to most carefully in the construction of a water-meadow on the first or second of these plans. First, no portion of them what ever should be on a dead level, but every part should belong to one or other of a series of true inclined planes. The second point of primary importance is the size and slope of the main conductor, which brings the water from the river to the meadow 7 . The size of this depends upon the quantity of water required, but whatever its size its bottom at its origin should be as low as the bed of the river, in order that it may carry down as much as possible of the river mud. Its course should be as straight and as near a true inclined plane as possible. The stuff taken out of the conductor should be employed in making up its banks or correcting inequalities in the meadow. Bedwork Irrigation. In this species of irrigation, which is eminently applicable to level ground, the ground is thrown into beds or ridges. Here the conductor should be led along the highest end or side of the meadow in an inclined plane ; should it terminate in the meadow, its end should be made to taper when there are no feeders, or to terminate in a feeder. The tapered end will retard the motion of the water ; and, as this contains, of course, less water, the water will overflow the banks of the conductor. The main drain to carry off the water from the meadow should next be formed. It should be cut in the lowest part of the ground at the lower end or side of the meadow. Its dimensions should be capable of carry ing off the whole water used so quickly as to prevent the least stag nation, and discharge it into the river. The stuff taken out of it should be used to fill up irregularities in the meadow. In case the river takes a turn along the lower end or side of the meadow, the turn should be utilized to carry oil the water. It might be imagined that, as a portion of the water will be absorbed by the soil, the main drain need not be made so large as the conductor, merely to carry off the water that has been used ; but in practice it will be found that, when the water is muddy, very little of it comparatively will enter the ground, the sediment acting as an impervious cover ing. The next process is the forming of the ground intended for a water-meadow into beds or ridges. That portion of the ground which is to be watered by one conductor should be made into beds to suit the circumstances of that conductor ; that is, instead of the beds over the meadow being all reduced to one common level, they should be formed to suit the different swells in the ground, and, should any of these swells be considerable, it will be necessary to give each side of them its respective conductor. The beds should run at or nearly at right angles to the line of the conductor. The breadt 1 of the beds is regulated by the nature of the soil and the supply of water. Tenacious soils and subsoils, with a small supply of water, require beds as narrow as 30 feet. Porous soils and a large supply of water may have beds of 40 feet. The length of tin- beds is regulated by the supply of water and the fall from the con ductor to the main drain. If the beds fall only in one direction longitudinally, their crowns should be made in the middle ; but, should they fall hiti-rnlly as well as longitudinally, as is usually