Weighing of specimens

The ASTM procedure covers the determination of the water absorption of cellular plastics (lighter than water) by measuring the change in buoyant force resulting from immersion. It can be applicable to WPC, having density less than 1.0, in its methodological part of underwater weighing of specimens. 

For accuracy of weighing, it is usually necessary to restrict the dimensions of specimens to what can be accommodated on the common analytical balances. It must be borne in mind that where attack occurs in the form of a very few pits or in crevices under supports, the extent of this localised... 

The most precise measurements of corrosion resistance require the use of specimens that can be weighed accurately after careful removal of corrosion products by the techniques described earlier. 

The specimen shall consist of approx 100g of the proplnt preferably as received. Weigh the specimen to within lOmg... 

The samples we used were vulcanizates of natural rubber (NR) and styrene-butadiene copolymer rubbers (SBR), carbon-filled and unfilled. Table 1 summarizes their preparative data. Incompressibility of these vulcanizates and some other vulcanizates were checked by dipping, stretching uniaxially, and weighing a specimen in water. 

It should be emphasised that in following the rate of dissolution of solid A in liquid B by the mass loss of a solid specimen of substance A, measured by weighing the specimen before and after the experiment, errors may well arise, due to the formation of a chemical compound layer at the solid-liquid interface. On the one hand, dissolution of the solid phase A in the liquid phase B reduces the mass of the solid specimen. On the other, however, formation of the ApBq compound layer adhering to the surface of the solid specimen increases its mass (at k0 > b). Hence, the experimentally determined change in the mass of the solid specimen is a consequence of the two simultaneously occurring processes, namely, growth and dissolution of the ApBq layer. 

If the thickness of the dissolved part of the solid specimen far exceeds the thickness of the ApBq layer formed at the solid-liquid interface in the course of dissolution, the error of determination of the mass loss by weighing the specimen before and after the experiment will be negligibly small. However, at low t and k0 > b the increase in the specimen mass due to the formation of the ApBq layer may prove greater than its decrease caused by dissolution. In such a case, instead of decreasing, the mass of the specimen will increase, as was observed, for example, by V.I. Zhalybin et al. during dissolution of titanium in the stainless-steel melt. 

For each experiment the weighed metal specimen is placed on the balance beam and checked for position and alignment. The balance tube is now sealed off and the apparatus evacuated to a pressure of 10-B mm. of Hg or better. Liquid nitrogen is placed in the traps during the process. 

When only a very small amount of specimen is available. (Specimens weighing as little as one milligram, or even less, can be successfully examined in a powder camera the diffractometer ordinarily requires a specimen of the order of half a gram or more.)... 

Naturally, leather absorbs some liquid water but mainly is water resistant. The leather industries do not claim that it is waterproof. So-called waterproof leathers are finished with water repellent agents such as organo-silicon, fluorocarbon and so on. Water absorption of leather can be tested by a static absorption method (ASTM D1815, 2000a). Cut the conditioned specimen with a circular cutter. Measure the diameter and thickness of the specimen. Calculate its volume in cubic centimetres. Weigh the specimen to the nearest 0.01 g. Immerse the specimen in distilled water at 23 1 °C in ahorizontal position with the grain side up. Leave the specimen immersed for a period of 30 min. At the end of immersion, take out the specimen and blot the surface of the specimen with filter paper to remove excess water. Weigh the specimen immediately to the nearest 0.01 g. Calculate the amount of water absorbed by the specimen ... 

The deposition kinetics were determined, either discontinu-ously by weighing the specimens after intermittent exposure, or continuously by measuring the extension of a silica spring balance. 

Pipette or weigh the specimen (1-5 g) into a Kjeldahl flask containing some glass beads. Add 3 ml suprapure nitric acid (65% v/v) and let stand for 1-2 h. Boil for 30 min till fumes of nitrogen oxide subside. Add 1 mL of perchloric (70% v/v) acid and continue heating till the solution is colourless. Add dropwise 2 mL of hydrogen peroxide (30% v/v) and continue boiling for 30 min. Cool and make up to volume (10-25 mL) with deionised or ultrapure water. 

The quantity of specimen that was placed in the measurement channel had no influence on the precision of the measurements. For this reason there was no need to weigh out the quantities of specimen used. 

It is possible to determine the four contributions to the total material loss rate by the following experimental principles the total material loss rate Wt is determined by weighing the specimen before and after exposure under combined erosive and corrosive conditions. The sum of Wc and Wce (the corrosion components) can be measured by electrochemical methods during the same exposure (the methods described in Section 9.2 can also be used under erosive conditions). We is determined by weighing the specimen before and after exposure in special tests where corrosion is eliminated by cathodic protection (or possibly by oflier means) but otherwise under the same conditions as in the former experiments. Wc can be measured electrochemically in tests like the original ones but with all solid particles excluded. Finally, the synergy components, Wce and Wec, can be derived from Equation (7.9) and the mentioned experiments. 

A circular sample of 74 mm in diameter is sealed over the open mouth of a cup containing water and placed in standard atmospheric conditions. The evaporation of water through the fabric specimen is observed by successive weighing of the cup after the specimen has reached equilibrium. The cup is filled with 100 ml distilled water and an air gap of 19mm is left between the water surface and the fabric. The air velocity over the specimen is maintained at 2.8 m/s, as shown in Fig. 2.14. After a suitable time, for example overnight, the dishes are reweighed and the time noted. The water vapour transmission is given by ... 

The compaction of specimens is carried out in five layers of approximately 127 mm thickness. Each layer is compacted by 56 well-distributed blows. In the case where the small mould is used, the layers shall be five, but each layer is compacted by 25 blows. Once the compaction has been completed, the surface is flattened with a straight edge and the material with the mould is weighed. Then, a representative sample is collected for moisture content determination. The moisture content of the sample w), as well as the dry specific gravity (apparent) (p ) of the compacted soil, is calculated using the following equations ... 

Once the immersion period of 48 h has expired, the surface of specimens is wiped with a towel and the specimens are weighed in air (M2). 

Confidence limits can also be used in cases where measurements are made on each of a number of specimens. Suppose, for example, that the mean weight of a tablet in a very large batch is required it would be too time-consuming to weigh each tablet. Similarly, if the mean iron content is measured using a destructive method of analysis such as atomic-absorption spectrometry, it is clearly impossible to examine every tablet. In each case, a sample could be taken from the batch (which in such instances forms the population), and from the mean and standard deviation of the sample a confidence interval could be found for the mean value of the quantity measured. 

---