Weighing and measuring

Liquids are measured out for a reaction by means of capillaries fitted with a rubber cap, a suction ball, a dropping tube, or a pipette. 

and other reagents should be kept as solutions of various known concentrations in this way they can be used in units of volume, making work more precise and faster. 

Micropreparative techniques require that liquids shall be measured from pipettes or, more rarely, from burettes. 1-ml and 2-ml pipettes with divisions in hundredths, and also 0.1-ml and 0.2-ml micropipettes with divisions in hundredths (error 3-5%), are used. Pipettes as used in blood-cell counts are useful for very small volumes, but each must be previously tared. Microburettes can be used for series experiments. A large number of precision microburettes with limits oferrorof only 0.01-0.1 % have been described in the literature. 

For very precise measurement of volume Pregl pipettes60 of 0.1-5.0 ml, tared for output, are used, but it should be noted that they are only wholly exact for liquids of rf420 1.0. 

Small amounts of solution of definite concentration can be prepared in small measuring flasks. An improved form of these measuring flasks, with 0.1-1.0 ml capacity and an error of only 0.5-1.0% has been described by Kirk.61 According to Gorbach,62 calibrated Pregl pipettes can also be used for this purpose. 

---

Weighing and measurements. The rough balances used for macro-scale preparative work are not adequate for senu-micro preparations. For the latter purpose, ordinary analytical balances should... 

Handbook 44, Specifications, Tolerances, and Other Technical Requirements Tor Weighing and Measuring Devices, National Institute of Standards and Technology, Gaithersburg, Md., 1996. 

Weighing and Measurement, Key Markets Publishing Co., Rockford, HI., pubHshed bimonthly. 

National Bureau of Standards Handbook 44 1979, Specifications, Tolerances and other Technical Requirements for Weighing and Measuring as adopted by the National Conference on Weights and Measures. NBS, Washington, DC, 1979... 

If experiments are to provide a valid source of information care must be taken about weighing and measuring. All ingredients must be from the same batch unless the test is to compare different batches of flour. In any tests there must be a control experiment lest a variation in, e.g. in the freshness of the yeast, masks a smaller change owing to some other factor. Another important point is that all experiments should be recorded. 

Weighing and measuring are two of the most important aspects of dispensing, compounding, and administration of medications. The present chapter deals with the fundamental operation of a prescription balance, an understanding of sensitivity requirement, an introduction to various devices used for measuring volumes of liquids, and their pertinent calculations. A knowledge of the systems of measurement, which is covered in Chapter 2, is essential to understand the material presented in this chapter. 

Mendeleviums chemical and physical properties are not well known because such small amounts with short half-lives have been produced. Many of its isotopes are produced just one atom at a time, making it difficult to weigh and measure samples. Its melting point is thought to be about 1,827°C, but its boiling point and density are unknown. 

Weighing and measuring equipment are of appropriate accuracy and are calibrated. 

For thin sheet material, it will be more expedient, and perhaps more useful, to measure mass per unit area rather than density. This is achieved by weighing a uniformly shaped piece of the material with known dimensions. Obviously, the density of any uniform piece of rubber can be obtained, at least approximately, but weighing and measuring all the dimensions in a non-contact manner. 

An autopsy can also obtain tissue slices for examination with a light microscope or an electron microscope. Furthermore, on gross examination of the brain, instead of estimating tissue loss from MRI pictures, an autopsy can actually weigh and measure the brain and examine cell density under the microscope. As a result, many diseases of the brain, such as Alzheimer s, require an autopsy rather than an MRI or CT scan to make the definitive diagnosis (Caine et al., 1995). 

Galileo showed men of science that weighing and measuring are worthwhile. Newton convinced a large proportion of them that weighing and measuring are the only investigations that are worthwhile. 

This brief review has shown that there are some differences in the way dietary risk assessment is practiced between the US and the EU. Many of the differences have to do in the types of input data that are available, or in some of the methods used to collect the data. Regarding the food consun tion data, the US surveys use a dietary recall method, whereas the UK approach is a diary method that weighs and measures the amount of food consumed. In the US, data are collected for two non-consecutive days, whereas in the UK surveys, data are collected for either 4 or 7 consecutive days. The US survey is conducted as an integrated whole and includes all segments of the population. In contrast, the UK surveys are conducted for specific population groups. Finally, the US survey collects data at the household level, whereas the UK survey targets demographic characteristics, based upon census information. 

All the scales for weighing and measuring must be properly calibrated and checked periodically. 

Ibid., pp. li-lA. As with the other challenges to customary measures, this one provoked municipal authorities and the populace to insist on weighing and measuring, in this case bakers loaves, to prevent such practices. 

True density is determined on a finely ground sample pycnometrically bulk density of regular shapes is determined by weighing and measuring the dimensions or by means of volumeters using non-wetting liquids that do not penetrate into open pores (e.g, mercury). 

---