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about 1000 feet, and such a very small condenser would flatten the wave front to 1000 feet length. With such a flattened wave of 1000 feet front, before full voltage appears at the transformer terminals, the beginning of the impulse is passed over ten or more turns, and the impulse voltage thus distributes over the insulation of a number of turns, and no difficulty exists to give the end turns an extra insulation sufficient to stand the voltage.
The foremost cases of high-frequency oscillations are spark discharges from the line, arcing grounds, etc. Their danger also is the piling up of voltage in reactive devices, such as current transformers, end turns of power transformers, etc. While a current transformer may take only a few volts at the normal frequency of sixty cycles, at 10,000 times this frequency it would take 10,000 times the voltage, and then break down between turns and between terminals. Inductance to reflect the high-frequency oscillation back into the line—which can stand it—with shunted capacity, and a non-inductive or, preferably, a capacity bipath to the inductive device such as the aluminum cell, offers protection against the danger from high-frequency oscillations. The best guard against interference by high-frequency oscillations is, however, to avoid all causes which may produce them, and the foremost cause is the arc. Thus arcs, arcing grounds, spark discharges, open-air switches, etc., should be carefully avoided in transmission systems, as introducing the dangers of high-frequency disturbances. This is to a large extent a designing problem.
In apparatus capable of electric oscillation,—that is, apparatus of high inductance, considerable capacity, but very low energy losses, such as high-potential transformer windings,—under certain conditions stationary waves may occur; that is, high-frequency impulses or oscillations, coming from the outside, built up by resonance to higher and higher voltages. Such stationary high-frequency waves are extremely destructive, as their energy is practically unlimited; is given by the low-frequency power of the system. Their frequencies usually are fairly low, between 10,000 and 100,000 cycles, and therefore it is more difficult to deal with them than with the oscillations of many hundred thousands or millions of cycles.
The best protection against them is not to allow them to build up. This is done by designing the apparatus so as to give the least ability to stationary oscillations, and by dissipating their energy, and thereby limiting their voltage, by shunted resistance. To avoid the excessive waste of power in such shunted dissipating resistances, a condenser of moderate capacity is connected in series with them. Such condenser practically cuts off the flow of power at the low machine frequency, but permits the flow of large currents through them into the dissipating resistance at the much higher frequencies of the standing waves.
In considering the protection of modern electrical systems it must be realized that the various sources and kinds of interference or danger require correspondingly different protective devices: it would be just as unreasonable to expect a standard type of " lightning arrester” to protect an electric system against all possible troubles as it would be to call for a single-standard “safety device” which would protect a railway train against all possible dangers, from a broken rail or a washout of the roadbed to a collision or a boiler explosion.
The Use of Copper Sulphate in the Purification of Swimming Pools. STANLEY JUDSON THOMAS. (Journal of Industrial Chenistry, vol. 7, No. 6.)-Within the past two or three years numerous articles have been written relating to the sanitary conditions of indoor swimming pools. One fact is emphasized by all authorities : that the danger of transmission of zymotic disease through the swimming pool is real. There is no doubt that hypochlorite of lime, which has been recommended as a precautionary treatment of public water supplies, is without a peer. It has been shown that 2.5 parts per million of hypochlorite of lime purifies the water shortly after its introduction into the pool, but it soon loses its germicidal properties. To add 2.5 parts per million of " hypochlorite ” every day would probably solve the problem from a bacteriological standpoint, but the odor would be too offensive for this form of treatment to be considered. The idea was conceived and acted upon of using a small amount of copper sulphate. The result of using 0.4 part per million of copper sulphate proved very satisfactory. From a comparative study and tests of the two methods of sterilization, the advantages of copper sulphate over hypochlorite of lime may be summarized as follows: (1) It is more effective, because it does not undergo chemical change readily. (2) It is not irritating to the eyes and mucous membrane, as is “hypochlorite,” if the latter is used in germicidal quantities. (3) It is cheaper. (4) It has no odor. If all other conditions were equal, this last fact alone would prove its great advantage over “hypochlorite."
BIOCHEMICAL AND ENGINEERING ASPECTS OF
SANITARY WATER SUPPLY.*
GEORGE W. FULLER, C.E.,
Member of the Institute.
This topic is a very broad one. In fact, some difficulty has been experienced in reaching a conclusion as to which particular aspects of this topic these remarks should be directed.
“ Biochemical” is not a very precise term. It is used differently by different persons. It is proposed to-night to speak more particularly of the biological rather than the chemical phases of this broad field which deals with the sanitary features of public water supplies. Reference will be made especially to means of measuring the sanitary quality of water supply through biological methods, and then of the accomplishments upon the public health of modern engineering works to conserve or improve the quality of water. The engineering works themselves will be scarcely touched upon.
While the main theme of this talk will be means of measuring the sanitary quality of public water supplies, both through laboratory procedures and the study of vital statistics, attention will be directed to some striking instances where it is proved that public water supplies are not wholly to blame for the prevalence of diseases generally associated with the public water supply. Other sanitary conditions are involved, and, as our knowledge of vital statistics and of modes of transmission of disease becomes more complete, it is shown that the city sanitarians have duties to attend to which in earlier years were assumed to belong to those who had charge of public water supplies.
This is a particularly apt time at which to speak on this subject. During the past week the United States Treasury De
* Based on a paper presented at the meeting of the Mechanical and Engineering Section held November 12, 1914. Manuscript received March 24, 1915.
partment has published a report of a Commission of Expert Sanitarians to specify bacteriological standards for drinking waters to be supplied to the public by common carriers in interstate commerce. That this task has not been an easy one is shown by the fact that it has required nearly two years of deliberations to formulate a six- or seven-page report.
Another feature of importance in the current developments of sanitary science on this side of the Atlantic is the work now being done by the International Joint Commission having control of the pollution of the boundary waters between this country and Canada. This has brought squarely to an issue the proposition of what is a reasonable load as regards pollution that modern water filters may be expected properly to carry. In populated regions surface waters of virgin purity are impossible. This does not mean, however, that pollution can not and should not be controlled within limits that will not prove overburdensome to those whose task it is to build and operate filters and other devices for the purification of public water supplies.
The Rivers Pollution Act of Great Britain, adopted in 1876, was so stringent that it had but comparatively little influence upon the public health, owing to the difficulty and great expense involved in adjusting to it. The Royal Commission on Sewage Disposal of Great Britain decided two years ago, after deliberating for more than a dozen years, that less stringent standards should be set up and that, furthermore, plans for completed works necessary for certain conditions might derive the benefit of “relaxation.” By this is meant that local authorities in Great Britain are to-day not obliged, in many cases, to build complete sewage purification works, although plans are to be prepared with that ultimate end in view, and that the construction work to that end must proceed in pursuance of local conditions both as to availability of funds for such work and as to local sanitary needs.
Laboratory methods for measuring the sanitary quality of water date back more than thirty years. They are contemporaneous in point of dates with the formulation and general recognition of the germ theory of disease and the transmission by water carriage of a number of the well-known diseases, particularly those of the intestinal group. Laboratory data do not afford a particularly satisfactory means of measuring the quality of water. They are simply a rough indicator, and the interpretation of the data seems to be positive and satisfactory only when they apply to a very good water or a very bad water. In the middle courses of the range of quality of water, laboratory data are to-day in need of further careful study, both as to methods in use and the interpretation of the results.
Following the Spanish-American war the sanitary world was shocked at the discovery of the extent to which disease was transmitted through the agency of flies and other insects. Those experiences were attained largely in the big army camps where the hygienic environment related more particularly to the conditions prevailing in rural rather than in urban communities. Gradually there has been determined the important fact that public water supplies are not in all cases responsible for the transmission of intestinal diseases to the extent which was hitherto thought to be the case. The recent evidence has been obtained for the most part in southern cities where the fly period is of longer duration than in the northern cities. In the latter, however, the fly period for quite a number of months each year has been a factor involving the public health to a degree much greater than has been recognized by the majority of sanitarians.
Some of the more important recent data will be shown with the aid of lantern slides to illustrate specifically these general remarks as to the need of more precise methods in the laboratory for the measurement of the sanitary quality of public water supplies; and, again, as to means of measurement of the effect of the public water supply upon the general health of the community through recognition of the influence of other aspects of municipal sanitation in bringing about high death-rates from so-called water-borne diseases, and in cases where the public water supplies are in no way at fault.
DETERMINATION OF SPECIFIC PATHOGENIC BACTERIA. Infectious diseases, such as may be water-borne, require the presence in the water of an appreciable number of the particular pathogenic bacteria producing the disease. It follows very simply, as an academic proposition, that if a correct examination of the water can show that no such disease germs are present, the water is safe for domestic consumption, and is what is generally termed "a wholesome water.” Unfortunately, such