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The present and increasing trend of present-day laboratories toward the use of instrumentation for chemical analysis, makes the regular monitoring of instrument performance an absolute necessity. Not least among the parameters, which must be monitored, is the possible presence in the output data of long- and short-term switching transients. Past efforts to eliminate the transients from analytical instrumentation by means of low-pass filtering techniques have heretofore met with almost complete failure. Adding excessive capacity to smooth out readouts has only slightly improved the adverse condition and at the same time has produced residual offset voltages, difficult to contain. it is virtually impossible to filter an interference condition where the true source identity is not established. This paper reports on the identification of the source conditions of two representative transients commonly present in and mixed with the output data from measurement instrumentation. The first transient analyzed is a pulse type associated with interference from triac switching. Its component angular velocity is such that voltages are transferred, almost unattenuated, through differential systems. In this condition, it acts as a low-impedance high energy source. The second transient analyzed is a sinusoidal wave type, often found as AC pick-up in high-impedance circuits. Once captured in a ground loop, it is extremely difficult to remove. The paper concludes with a complete characterization of these conditions, describing direct methods for shielding, filtering and offsetting their effects.

In order to calibrate the electronic portion of pollution monitoring equipment, it is desirable to have electronic standards that operate over the range covered by the primary detectors. This paper describes active standards of current, voltage and resistance, directly related to this type of equipment. In addition to this, methods are discussed by means of which these standards may be used effectively. The paper concludes with the concept of the specific source characterization of electricity in support of active standards.

This paper, in taking a photometric mercury monitor as a model, shows four routes, by way of which interference may enter into the measurement stream of monitoring equipment. It relates the effect of this interference to the problem of zero-stability, calibration and sensitivity. It clearly shows that the practices of shielding, wire dressing, and circuit function isolation, often ignored, must be strictly adhered to if maximum performance from any instrument is to be realized.

Although many authorities accept fluoridation of water as a safe and effective means of preventing caries, there is no consensus in the scientific literature as to the maximum safe daily intake of fluoride from all sources. Further, only a small amount of up-to-date information exists for the fluoride content of foods and beverages other than water. This paper is concerned with infant nutritional regimens and shows that fluoride added during processing may contribute toward substantial unexpected ingestion of fluoride. For some typical regimens fluoride ingestion from only one or two items in the diet may be larger than the maximum safe daily intake recommended by some authorities.

This paper is concerned with the effects of reservoir construction on downstream water temperatures. Following an outline of the general mechanisms involved in such thermal modifications, a case study of the Yorkshire Lune employing field observations collected over a two-year period is then described. Emphasis is placed on the extent to which the natural range of stream water temperature variation is suppressed by the two direct-supply reservoirs on this river.

Knowledge of the world-wide atmosphere is quite incomplete, despite the considerable investigative efforts expended upon it. Nevertheless, recent studies have resulted in some knowledge of its constitution and chemistry from all of the fifty states in the U.S.A., Western Europe, Panama, Amazonia, both polar regions, and selected portions of the Atlantic and Pacific Oceans. The remainder has been but little observed. Despite the geographic differences in topography, climatology and civilization, the world-wide atmosphere has been found to be similar at moderate distances (a few kilometers in the vertical or a few tens of kilometers in the horizontal direction) from particular sources. The atmosphere may be divided in several ways. Excluding the stratosphere, we may take the mixing layer and the remainder of the troposphere, or we may take urban, rural and remote divisions, or we may take polluted and unpolluted divisions, among various choices. The last divisional scheme is considered in this paper.