True moisture content

From the excellent agreement in measurements by the various methods Sair and Fetzer concluded that they have determined the true moisture content with an accuracy of approximately 0.1%. Though this claim is subject to further verification, it does indeed seem to be plausible. 

A d.c. insulation resistance test or polarization index reveals only the surface condition of the insulation and does not allow a realistic assessment of internal condition. Loss tangent values are true reflections of the insulation condition to detect moisture content, voids, cracks or general deterioration. The tan 5 versus test voltage curve may be drawn and compared with the original curve provided by the manufacturer, and inferences drawn regarding the condition of the insulation. The different starting tan lvalues will reveal the condition of the insulation in terms of amount of contamination, as noted in Table 10.4 (See lEE, Vol. 127, May 1980). 

There are, of course, occasions when vapor pressure data are not sufficient, and the moisture content must be known, as will be true, for example, in certain engineering cal-... 

A similar picture is shown by the subbituminous coals in the northern foreland of the Alps where the lines of equal moisture content also cut the bedding planes (Figure 15). It is true that in the Hausham Syncline the moisture content of the vitrites decreases with increasing age of the seams, but on the other hand there also is a distinct relation between the moisture content and the present depth of the seams. It is striking that the lines of equal moisture content stand oblique. This may result from the uplifting of the Alps which is still proceeding. 

Food yeast, molasses-grown, is dried to about 5% moisture and has the same chemical composition as bakers yeast. In terms of micrograms per gram of yeast, the vitamin content is 165 thiamine 100 riboflavin 590 niacin 20 pyridoxine 13 folacin 100 pantothenic acid 0.6 biotin 160 para-ainiiiobeuzoie acid 2710 choline and 3000 inositol. YeasL crude protein contains 80% amino acids 12% nucleic acids and 8% ammonia. The latter components lower the true protein content to 40% of the dry cell weight. 

Similar comments apply to the apparent °Brix and true percent-weight concentrations determined by density/specific gravity measurement. Assuming the percent-weightconcen-tration is accurate, for a concentration of x (wt%), moisture content is (100 -x)%. 

Clearly, the calculation of moisture content by difference, whether using hydrometry or refractometry to obtain estimates of solute concentration, is an approximate method. Its utility depends upon there being a repeatable correlation between either density or refractive index and the true percent weight concentration of the solution. This repeatability is dependent upon the exact composition of the solute system. 

The infrared moisture analyser may also be used for quick determination of water content although it gives a value that is different than the other two methods (subject of a future unit on NIR). This may be useful if a rapid IR method is used in a production line so one can correlate line moisture with true moisture. 

The composition of the soil solution changes constantly as elements dissolve, desorb or decomplex from the solid phases, as plant roots and lower plants withdraw nutrients or release organic substances, as rainwater brings in solutes from outside and as the soil water passes down the profile into the drainage water. Figure 1-4 summarises these processes. It should be noted that equilibria are assumed between the solution and the matrix components but there is no certainty that rapidly fluctuating moisture contents will allow true equilibrium to be attained. 

Related Calculations. Use the method given here when making combustion calculations for any type of coal—bituminous, semibituminous, lignite, anthracite, cannel, or coking—from any coal field in the world used in any type of furnace—boiler, heater, process, or waste-heat. When the abused for combustion contains moisture, as is usually true, this moisture is added to the combustion-formed moisture appearing in the products of combustion. Thus, for 80°F (300 K) air of 60 percent relative humidity, the moisture content is 0.013 lb per pound of dry air. This amount appears in the products of combustion for each pound of air used and is a commonly assumed standard in combustion calculations. 

Intermolecular association in DNF with moisture content and dioxane, making the true aspect ratio of the statistical object in solution these solvents uncertain. If the effective macromolecular length increases due to association, the volume fraction for incipient liquid crystal formation would be expected to be lower. 

Available techniques make it possible to measure the true density of wood (at a given moisture content). These include special procedures to obtain dry-wood volumes (25), as well as special methods using p-ray or X-ray technology (26). However, these procedures are not easily applied in a routine fashion, on a large scale, or on large wood specimens. 

At the cellular level, the true density of dry cell wall substance (i.e., within the cell wall) has been determined to be about 1.5 g/ cm, varying to some extent with the method of measurement and species (2). There are voids within the dry wood cell wall, but the void volume here (i.e., micropores) is reported to be only about 2-4%. However, this figure would be expected to increase as wood moisture content is increased to the fiber saturation point (28). 

A resistance meter reads moisture contents higher than the true values when used on hot wood, and vice versa for cold wood. Therefore, the readings must be adjusted for this temperature factor. A family of curves used to adjust measurements made on wood at temperatures from -40 F (-40 C) to 160 F (71 °C) is reproduced in Figure 3 (J4). It is probable that individual species, in addition to showing variations from the standard curve of resistance against moisture content, also show variation with respect to the temperature adjustment factors (JO). Some modern meters are provided with adjustable meter calibration for direct temperature compensation (JJ). 

Hygroelastic Effects. When hygroscopic materials such as wood are restrained from swelling freely they not only exert a swelling pressure but also come to a lower moisture content than if unrestrained. The reverse effect also holds true wood restrained from shrinking exhibits a higher equilibrium moisture content than if unrestrained. This is the hygroelastic effect, sometimes called the Barkas effect because Barkas was the first to treat it quantitatively (26). 

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