SINCE the author made the first tests as to the tarring of macadamized and… ather roads about ten years ago, the question has been taken up in France by the Dust Prevention League, and the results were discussed at the International Cangress of Roads held at Paris in 1908 and at the Brussels Congress of 1910. Since that time, it may be said that surface tarring has entered into standard practice. As regards the question of hygiene, it appears that the desired end has already been reached, inasmuch as the amount af dust is much lessened. The other paint to be considered is that of cost. All road engineers are agreed that tarring has the effect of lessening the wear of roads and increasing the life of the pavement, to say nothing af the reduction in street-cleaning expenses, including watering, mud removal, and sweeping. But it was somewhat difficult up to the present to give any good figures for the economy realized on any given road. In fact, it requires a certain time to estimate the economic results as to upkeep of a road where the nature and amaunt af traffic vary considerably from one year to another. At present we are able to give some figures relating to the Avenue du Bois de Boulogne, a wide avenue leading out to the large park of the same name. The figures are given by M. Bret, ane af the city engineers. This avenue is one af the finest in Europe, measuring 0.93 mile in length and 53 feet in width, and being bordered by a riding track and a footway. The total surface is 25,466 square yards. It was newly macadamized in September, :906, and was first tarred in May, 1907. Since then it has not been macadamized; before the tarring was adopted it had to be re-laid every three years. The figures for expenses were drawn up for three and one-half years preceding the tarring, then for four years afterwards. Comparison of the figures shows that the annual saving up to the present is 11 cents per square yard, or about 25 per cent on the re-laying and upkeep expenses alone, not counting the economy on cleaning expenses. It is noticed that the road was tarred only once in 1907, and after 1908 it was tarred twice a year, in spring and autumn. The author, who is a leading official of the league, arranged with the city engineers so as to have tarring done in autumn in order to have a fresh surface for the winter traffic. The result was striking, and in the spring following it was found that the surface was still in a very good state and the tar had remained on the greater part of the road surface, except in the middle where it had commenced to wear off. The Economic question involved appears to be settled, and the life of the road may be considered as doubled, so that the tarring! expenses are more than made up by the increased wear, as above shown. On the other hand, the frequent relaying of ordinary roads, which requires two months, causes great disturbance in the traffic, while the tarring process needs but a few days in order to allow the tar to dry. As regards the efficiency of the process in laying dust, the results are remarkable. Before this, the avenue in question had to be frequently sprinkled in the hot season every two or three hours, but one washing per day is all that is now required, and no one complains of the dust. Many thousands of automobiles per day pass over the avenue, so that at certain times, it used to be almost impossible to carry out the sprinkling; hence arose great clouds of dust and much discomfort and spoiling of clothes_ At present this has disappeared, and all agree as to the benefits of the tarring process. It would be too much to say that tarring could be carried out with equal advantage on all kinds of macadamized roads, for in the present case the traffic, No-Tank you! 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So we are making a great, special money saving offer on Columbia Kerosene Engines. This offer is liable to be withdrawn at any time. 80 write today for full particulars, for it is a money saver you would hate to miss. Free Book No. 8 full of engine facts yon need to know, sent free. Shes 2 to 16 H . P. Columbia Engine Co., 96 Fullo' St., Detroit, Mich., U. S. A. DOUBLE THE FERTILITY OF YOUR FARM By Breaking up the Rich Subsoil WITH RED CROSS DYNAMITE Ordinary plowing turns over the same shallow top-soil year after year, forming a hard and nearly impervious plow sole that limits the waterholding capacity of the land and shuts out tons per acre of natural plant food. Dynamiting the subsoil makes this plant food available, aerates the soil, protects vegetation against both drouth and excesS rainfall, and soon repays its cost in saving of fertilizer expense and largely increased yields. Write for Free Booklet To learn how progressive farmers are using dynamite for removing stumps and boulders, planting and cultivating fruit trees, regenerating barren soil, ditching, draining, excavating, and road-making. Write now for Free Booklet-"Farming with Dynamite, No. 29. E. I. DU PONT DE NEMOURS POWDER CO. PIONEER POWDER MAKERS OF AMERICA ESTABLISHED 1802 WILMINGTON, DEL., U. S. A. though dense, consists exclusively of light private vehicles, as the road is closed to heavy conveyances. In considering the question we must see what roads , are best adapted to the tarring process. The failure properly to take into account this factor may explain the want of harmony between the city engineers having charge of streets and the engineers occupied with country roads. which was noticed at the Brussels Congress. The city engineers favored the suppression of macadamized roads in cities and considered that such .should be paved with stone, wood, or asphalt as traffic increases. Opposed to this opinion were the other road engineers of nearly all the nations represented, and they showed the- good results which road tarring had given, claiming that in towns having a lighter traffic this could be used to advantage. To conclude, a judicious choice should be made, and the tarring should not be done on macadamized roads where the heavy traffic required a re-laying every two years or even once a year. Such roads should certainly be paved, reserving the tarring for other kinds of ways. The question, however, has been raised as to whether tarred roads have not a bad effect on the eyes of drivers and also upon trees and plants which border the routes. As to the harm done to the eyes, proof appears to be wanting, as the road from Paris to Versailles is entirely tarred, as well as the above-mentioned avenue, and we hear of no serious complaints for eight or nine years past, nor upon the roads in the south of France around Nice, where the dust is much greater, Laboratory experiments as to the effect of such dust on animals' eyes are of no avail, as any kind of dust is of course bad for the eyes. Opinions are divided as to trees and! flowers. Plant· growers claim that dust and tar·vapors cause harm, while engineers think this is exaggerated. At Paris, the opinion is in favor of the tarring, in spite of any sIight harm that; may be done, owing to its other advantages. Dr. Griffon, in a paper read be·, fore the Academy, speaks first of tar vaporS and then of dust. Vapor is bad for plant cells in laboratory tests, but this is not conclusive, as in reality such vapor must be very weak. He noticed that after the spreading and during the hardening of the yet unused roads, no effect was seen on the plants. As to dust, this has some effect on weak plants such as the begonia and others, which is not given from ordinary roads, but trees and shrubbery, also most plants and flowers, appear to show no harm. Leaves of trees may become brown or withered, but this often occurs in city streets, and is due to other causes. On the whole, his extensive inqUIrIes in France and England lead him to favor the tarring. No complaint apears to be heard in other countries. Since 1910, over 10,000 miles of road has been tarred in England, and the review The Surveyor does not note any serious injury to the eyes nor to plants. In Germany the same opinion appears to prevail, as also in Belgium. Owners of villas and gardens in the Riviera are among the most prominent members of the league, showing that they still favor the tarring. One reason for this latter opinion is that the plants in the south are of stronger growth, which leads to the opinion that the plants on Paris avenues should be changed. To bring out the question, the Prefect of the Seine department lately appointed a commission of leading experts. Shrubbery and various plants will be set out along tarred and un· tarred routes to compare results, and laboratory tests will be made upon any spots occurring in leaves. Attempts are made to purify tar and some samples are now produced which are much less harmful to plants and come near to Norway tar, which is quite inoffensive. It remains to be seen whether this will be economical or not, In any case, it seems evident that it is better to change the plants than to abandon the tarring, owing to its disadvantages. Dust also needs to be suppressed as much as possible. Even while no dust comes from the wear of the road itself, such is urought from the outside by wind or vehicles. The road should therefore be properly watered, and the author proposes to use one of the recent oil products which mix with the water, such as Instructive Books Gas, Gasoline and Oil Engines; Including Producer-Gas Plants By GARDNER D. HISCOX. M. E. 6)^ x 97 inches,. 476 pages, 412 illustratIOns. Cloth. Price, $2.50. t This new revised and, enlarged edition is a.. comprehensive and thoroughly up-to-date work, and treats fully on the construction,. installation, operation and maintenance of gas” gasoline, kerosene and., crude petroleum engines. It treats on the gas, gasoline and oil engine: as designed and manufactured in the United States, the stationary, marine and vehicle engines, their theory, care· and running. Electric ignition by induction coils and jump sparks are full y-explained and illustrated. Practical Steam and Hot Water Heating and Ventilation By ALFRED G. KING. 6% x 97 inches. 402 pages, 304 illustrations. Cloth. 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Price $2.00. Catalog free. OlNIGRAPlI MFG. CO. Dept. 16. 39 Cortlandt Street, New York. SCIENTIFIC AMERICAN 54.7 "Westrumite,” and this will aid in keeping down the dust. The Crusade Against the House Fly Of July 24th, there was instituted in Washington, a most interesting crusade against the common house fly. For several seasons one of the leading daily newspapers of the capital has been printing in display type the legend SWAT THE FLY, but this summer this same paper began its campaign in earnest. Realizing that it is human nature to desire a pecuniary incentive for any public service, several hundred dollars in prizes were offered, one hundred dollars being the grand prize for the greatest number of flies killed, and many other prizes of lesser amounts representing first, second, third and fourth prizes, etc. Only children under the age of sixteen were permitted to enter, the fly-swatting contest. Each contestant is furnished with a fly swatter, and paper boxes for the dead fies were distributed. Each day the boxes contairing the offerings of the workers are collected and the flies so exterminated are first counted at the Health Office, and then cremated. The first five days of the campaign saw the leader in the contest with the proud record of 40,000 flies killed. with a long list of those who had more than 20,000 to their credit. It is interesting to note that the children have organized themselves into squads and range over several blocks of territory, killing the flies in kitchens, grocery stores, stables and refuse heaps. Even out of doors the fly has no peace, but is kept busy dodging this veritable army of determined swatters. Up to date, by actual count, more than 2,000,000 of these pests have been exterminated, and the service performed in the interest of public health is enormous, when compared to the comparatively small outlay of money. The only pity of it is that the campaign had to be financed entirely by private means, and that the municipality of the District of Columbia could not “raise the ante” and make the prizes attractive to grown persons as well. It is not expected that in four weeks of the Evening Star's contest, Washington will be reduced to a state of absolute flyless-ness, but that there will be a slump in next season's crop there is not the slightest shadow of doubt. ConSidering the propagating possibilities of the fly, it would seem worth while for other cities to follow Washington's example in this regard and get the children started. Think of the enormous slaughter of flies there would be on the East Side, for instance, if the myriads of kids, excited by the prospect of winning a handful of dollars, could be induced to “swat the fly." Restoring Hardened Rubber. -Everyone is familiar with the very undesirable change to wnlCh rubber is subject on prolonged standing, such articles as rubber tires becoming hardened and brittle. According to a note published in the Motor World, there is a simple remedy for this trouble, provided it has not gone too far. This consists in immersing the article for a short time in an alkaline solution composed of one part of ammonia to two of water. As an example of the efficiency of this process, an old bicycle tube which seemed beyond restoration was found quite fit for use after half an hour's immersion in such a solution. In explanation of the effect it is supposed that there is a tendency for acids to be formed in the rubber, and that these acids are neutralized by the alkaline solution. On the strength of this, it is suggested that when tubes or other rubber articles are stored, a small quantity of quick lime or ammonium carbonate be included in the wrapping, though it could be kept from actual contact with the rubber. Periodic washing with ammonia and water is also suggested as a preventive. Boston Street Lighting. -The total number of lamps on Boston's streets on January 10th of this year comprised 3,973 arc lamps, 1,206 tungsten incandescent, and 11.742 gas. During the year 1910 the cost of electric lighting was $408,900; that of gas lighting, $277,256. Naphtha lights were used in small numbers during the year at a cost of $1,833, but all of these have now been replaced with gas lights . Municipal Journal. Do you send Valuable Packages by Mail? Government rates 150% higher than Hartford Mail Package Insurance AS a business man whose business requires _C\^ the use of the U. S. 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