1850.1 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL 



263 



heated and burned by the strong rays of the sun; and when there 

 is much organic matter in the water it becomes a living mass of 

 animalculae, and even at some times will be found frogs, and great 

 numbers of tadpoles. This living mass, of course, causes the sand 

 to silt up much sooner, but generally does not affect the purity of 

 the water when filtered, being entirely excluded by the material 

 in filter bed; but the strong rays of a summer sun beating on the 

 surface, by burning it, as it is termed, tends to give the water a 

 slight taste and light brownish colour, which, although not to be 

 detected in small, is quite perceptible in large quantities. Among 

 bleachers this effect of the sun is a well-known fact, their pure 

 water, by this cause, being not unfrequently rendered unfit for the 

 required purpose. In order to avoid this, and still dam back 

 the water, a sluice should be fixed on the outlet, by means of which 

 the superintendent, during summer, can gradually raise or lower 

 the level of overflow at said outlet, as he "observes the water rising 

 or falling in filter bed; by this means he can prevent the water 

 from spreading on the surface in a thin sheet, and from being 

 exposed and burned; and put a stop, to a great extent, to the rapid 

 increase of animalculae; and as fur tadpoles, they could not exist. 

 In cold weathei the same precaution becomes unnecessary; in fact, 

 at such seasons, the water is improved by being exposed in thin 

 sheets to the influence of the sun and air. 



For the cleansing of filters the system now sometimes adopted 

 is, that of reversing the direction of the water, and conveying it 

 away by drain, after coming to the surface, mixed with the silt. 

 Sometimes the surface of bed is scraped — the former is, however, 

 the better system; but on account of its not being suflSciently 

 effectually applied, caused by the openings into drain not being 

 properly placed, and the water sent up from below not sufficient 

 either in quantity or pressure, in all cases where it has yet been 

 applied its effect has been very partial, and recourse is not unfre- 

 quently had to the scraping besides; but even in such cases, 

 although its effect in removing the silt is so deficient, still it has 

 the tendency to improve the workiug of the filter bed, owing to 

 the material being rendered more loose and open; and when often 

 repeated, the filter bed will continue to act for a considerable time, 

 even after it has become very much loaded with impurities. 

 Filters for this system of cleansing are generally constructed with 

 a false bottom, formed by brick on edge, supporting perforated 

 tiles, the water being let into this space by means of openings or 

 pipes when the bed is required to be cleaned. 



Filters, in order to be properly cleansed by this system, should be 

 so constructed as to admit of a large body of water being forced 

 from below with sufficient pressure, so as to boil up and agitate the 

 material of the filter bed, in order to free the sand of the silt; and 

 still farther, to i-emove the impurities from the jiarticles of the 

 sand during the time that the upward current is going on, it 

 should be well raked with a large rake; or a harrow, loaded to 

 keep it from floating, having ropes attached, and drawn backward 

 and forward by two men, would answer better. The effect of this 

 raking, besides loosening the impurities, tends to spread the boil- 

 ing-up of the water equally over the whole surface, and not in 

 detached patches, as is otherwise found to be the case. By this 

 means, the water from below, as it rises and spreads itself over the 

 bed of filter, will gradually get loaded with inipui-ities; and while 

 thus loaded, were it conveyed to a drain, with a current sufficiently 

 strong, so as to prevent these impurities from again settling on the 

 sand, the object aimed at would be attained. In order to get a 

 sufficient current to effect this purpose, the openings into drain 

 should be on the same level as bed of filter, and so arranged that 

 the run into each will be short — say about 20 feet. On di-ain, a 

 sluice should be placed, so that when down the water would be 

 prevented from getting away: it would thus keep gradually rising 

 in the filter-bed, and if, after having acquired a depth of from 8 to 

 1'2 inches, this sluice was opened, owing to the short runs and the 

 depth of water, there is little doubt but a strong current would be 

 obtained, and the higher the water was allowed to rise before 

 opening the sluice, the greater of course would be the current. 

 In some existing filters, to cause a current, the water is let on to 

 the surface at the same time that it is kept rushing up from below; 

 by this system, however, it is clear there is a great loss of water, 

 while it acts only a secondary part in the operation. But by taking 

 all the water from below and creating a current by the system I 

 have here mentioned, there is no waste of water, that which is 

 used being all fully got advantage of, both foi the purpose of 

 freeing the material in filter-bed of the silt, and for creating a 

 current to carry it, when loaded with the impurities, quickly into 

 drain. 



In order that the false bottom be enabled to stand the pressure 



of the water, it should be made much stronger than is generally 

 done; the holes in tiles larger, so as to admit of the water getting 

 freely up amongst the material; and to prevent the sand escaping 

 from' these openings, the tiles should first be covered with a layer 

 of broken stones and gravel. 



In the filtering of water, it is sometimes passed through various 

 beds of different degrees of fineness, and sometimes only one. In 

 cases where the water, by subsidence, can be rendered tolerably 

 pure before being filtered, one large bed will be sufficient; but 

 where its purity may vary much, more beds become necessary. In 

 most cases two beds wiU be found quite sufficient, the one filled 

 with a good thick bed of coarse gravel, and the other with good 

 coarse silicious sand. If a sufficient quantity of coarse gravel 

 cannot be easily obtained, broken granite, trap rock, or hard gritty 

 freestone, will, as I have already observed, suit exceedingly well, 

 continue in good working order for years, remove a large propor- 

 tion of the grosser impurities, and thus render the water, before 

 being let on to the sand bed, more equal in purity during all 

 seasons. 



In concluding these remarks on the purifying and filtering of 

 water, I may here simply observe, that in the construction of all 

 filters connected with waterworks for supplying large and populous 

 towns, in order that they may be cleansed without causing the 

 necessity of supplying unfiltei-ed water, the filter bed should be 

 divided into water-tight comparments, so as to admit of one part 

 being cleansed while the others are in full operation. 



BRIDGE BUILDING IN AMERICA. 



At the Franklin Institute (U. S.), Mr. Solomon W. Roberts 

 made some remarks upon bridges. He referred to the importance 

 of economy in their construction, as large sums were often expended 

 in such structures, when a less amount would answer the purpose. 

 Suspension bridges, supported by iron chains or wire cables, sub- 

 jected to a tensile strain, are comparatively cheap. When the 

 material used is wrought-iron it is easy to make strong splices, 

 but this is not the case with wood. Suspension bridges on a large 

 scale cannot readily be built of wood, on account of the difficulty 

 of tieing the timbers securely together and holding them fast. 

 The bridges built by a person named Remington, about which a 

 good deal was said in the newspapers not long ago, were wooden 

 suspension bridges, on a small scale. It is believed that the first 

 rude suspension bridges ever made were constructed of grape vines 

 or some similar materials of vegetable growth. They were, of 

 course, but of small dimensions. 



The railroads of our country abound in examples of economical 

 bridge-building; and when we are informed that more than three 

 millions of dollars have recently been expended in England, in 

 building a railroad bridge about fifteen hundred feet long and one 

 hundred feet high, it seems almost incredible. No doubt the 

 difficulties were great, and no doubt the bridge in question is a 

 magnificent structure: but a person accustomedi to the exigencies 

 of engineering in America shrinks from the idea of such an outlay 

 of capital. 



The wagon bridge across the Niagara river, below the Falls, is 

 a cheap structure, the span being about seven hundred and fifty 

 feet, and the lieight more than two hundred feet. It is understood 

 that, at the same point, two able, experienced, and responsible 

 engineers have offered to contract to build a substantial bridge 

 for railroad trains across the most terrific torrent on the globe; 

 and that the price asked by one was two hundred thousand dollars, 

 and the other one hundred and ninety thousand dollars. At such 

 prices the bridge would cost but little, if any, more than the 

 interest for one year, at six per cent, of the cost of the tubular 

 bridge across the Menai Strait. The cases were not alike, but 

 they might serve to draw attention to the different circumstances 

 under which engineering works, ai-e executed in England and 

 America. — Journal of the Franklin Institute. 



The New American Gas Light. — By our advices from the United 

 States, we learn that the excitement is still very great about Paine's system 

 of gas-lighting hy decomposing water. It is looked upon as one of the great 

 discoveries of the age, and very strong certificates are given by those who 

 have seen the apparatus at work, the only part kept secret being the inte- 

 rior disposition of the electrodes. A very strong controversy rages abo\it 

 Mr. Paine's abilities as an engineer, but it is certain he has long held a good 

 standing among the practical men of his locality. Enormous sums are 

 offered for the patent, in case he succeeds in lighting Astor House. 



