Precision weighing

Another anomalous property of some nickel—iron aHoys, which are caHed constant-modulus aHoys, is a positive thermoelastic coefficient which occurs in aHoys having 27—43 wt % nickel. The elastic moduH in these aHoys increase with temperature. UsuaHy, and with additions of chromium, molybdenum, titanium, or aluminum, the constant-modulus aHoys are used in precision weighing machines, measuring devices, and osciHating mechanisms (see Weighing AND proportioning). 

VOLUME.dat Section 1.1.2 A set of five precision weighings of a water-filled 100 ml flask the weights in grams were converted to milliliters using the standard density-vs.-temperature tables. Use with MSD to test the effect of truncation errors on the calculation of the standard deviation. (See Table 1.1.)... 

Fractionation. The process by which components are extracted firm bacterial eells or from the medium in whieh the baeteria are grown and obtained in a purified form. The polysaccharide antigens of Neisseria meningitidis are separated from the bacterial cells by treatment with hexadecyltrimethylammonium bromide and those of Streptococcus pneumoniae with ethanol. The purity of an extracted material may be improved by resolubilization in a suitable solvent and precipitation. After purification, a component may be dried to a powder, stored indefinitely and, as required, incorporated into a vaccine in precisely weighed amounts at the blending stage. 

Now let us start this discussion by assuming we have a known analytical value by artificially creating a standard sample using impossibly precise weighing and mixing methods so that the true analytical value is 5.2% analyte. So we make one measurement and obtain a value of 5.7%. So then we refer to errors using statistical terms as follows ... 

Of particular interest are quantitative syntheses of extremely deliquescent and reactive alkyliminium salts by milling of solid imines with oxonium salts (178), triphenylmethylium tetrafluoroborate (180), or triphenylmethyl chloride (183) (dry atmosphere in these cases). The sensitive salts 179, 181, and 184 are formed in pure form without any waste by an easy experimental technique [10]. Precisely weighed samples of 178 (ca. 2 mmol), 180 (ca. 1 mmol), or 183 (1.00 mmol) were placed in a ball-mill under argon together with the precise equivalent of 54a,f,g, or 54f, or 182, respectively. The Teflon gasket was closed... 

The arylmethylene imine hydrochloride 2 was sampled under dry argon, precisely weighed (ca. 2 mmol) and ball-milled with the equivalent of 2-naphthol 1 for 1 h. The solid-solid character was finally lost during the reaction as the material became sticky. The free base 3 was obtained after neutralization of 3 HC1 in CH2C12 by washing with NaHC03 solution and crystallization from ethanol. 

Diermayr, E., and A. Holasek A High-Precision Weighing Pipet for Milliliter Volumes. Microchem, J, 10, 231 (1966). 

The method proposed by Horii et al.13 was used for the measurement of free amino acid. The SC was stripped with adhesive cellophane tape (Cello-tape, Nichiban Co. Ltd., Tokyo, Japan). The tape was immersed in toluene to remove the SC, which was then washed with toluene several times and dried in a vacuum desiccator. One milligram of dried sample of SC was precisely weighed and homogenized with 0.1 % of sulfosalicylic acid. After centrifugation the supernatant was analyzed with a high-speed amino acid analyzer (Model 835, Hitachi, Tokyo, Japan) to determine the level of total... 

Many operations within the laboratory start with weighing. It is difficult to undertake precise weighing in conventional laboratory fume hoods, as the airflow and vibration inside an operating fume hood often disturb the balance. In order to accommodate the need for an engineered control at this scale of operation, dust control systems have evolved known as ventilated weighing safety enclosures or powder weighing hoods. Key characteristics of a ventilated weighing safety enclosure include ... 

One of the most important of these new experimental tools has been the development and application of the vacuum microbalance technique in which the sensitive microbalance operates directly in the vacuum or reaction system. The success of the method depends upon the coordination of a number of different experimental as well as theoretical disciplines. Thus, from an experimental point of view precise weighing techniques on properly prepared specimens must be coordinated with high vacuum techniques and the use of ceramic materials at high temperatures. From a theoretical viewpoint thermodynamic calculations must be made for all of the reactions involved and the results interpreted in terms of diffusion process for gas-solid reactions in which a film is formed or the gas diffuses into the solid, or in terms of the absolute reaction rate theory or its equivalent for gas reactions on solids including catalytic reactions and the combustion of fuels. 

Enzyme solution. Powdered invertase obtained from yeast is available from mai r biochemical supply houses, such as Sigma Chemical Co., P.O. Box 14508, St. Louis, MO 63178. A sterile solution of invertase must be prepared with great care. All apparatus used to make up this solution must be sterilized prior to use. More than 1 L of distilled water is boiled for 10 min, covered with aluminum foil, and chilled in an ice bath. Then add a precisely weighed amount of invertase (approx. 5-10 mg) to water in a 1-L volumetric flask and make up to the mark. The enzyme solution should be kept tightly stoppered and chilled at all times. The correct invertase concentration is very sensitive to the specific activity of the enzyme as purchased it is necessary to carry out the standard assay and adjust the solution to an appropriate final concentration. 

In top-loading versions of the electronic balance, the weighing pan is supported on an upward extension of the moving bar of the parallelogram. This type of balance is very convenient for moderate precision weighing operations, and such balances have capacities of 0.1 to 10 kg with a precision of 1 mg to 1 g. Hybrid versions (electronic-mechanical balances) have also been produced, particularly for low-capacity (<10-g) micro and ultramicro balances these have a precision of 0.1 to 1 jU-g. 

Oxidation weight gain was calculated by precisely weighing both treated and untreated PCS samples after leaving them in a silica gel desiccator for more than 1 h and using equation 1... 

Aqueous solutions of the amino acid L-lsoleucine (lie) are prepared by putting 100.0 grams of pure water into each of six flasks and adding different precisely weighed quantities of He to each flask. The densities of the solutions at 50.0 0.05 Care then measured with a precision densitometer, with the following results ... 

The AC o polymers are resistant to oxidation in air and remain intact in solvents like toluene [11], This is in contrast to all other known alkali fullerides, including the fee high temperature AC o phases, which rapidly degrade in air. The air stability facilitates experimentation and the stability and the insolubility in solvents provides a mean for separating the polymer phase from other phases. Doping pure with precisely weighed amounts of alkalis at high temperatures is the usual synthesis of AQg compounds with A = K, Rb, Cs. The exact stoichiometry is hard to achieve and most early data are on mixtures of different phases. 

To find the concentration of the solution being titrated, you must, of course, already know the concentration of the titrant. A solution whose concentration is already known is called a standard solution. The concentration of a standard solution has usually been determined by reacting the solution with a precisely weighed mass of a solid acid or base. 

Precisely weigh (to the nearest 0.1 mg) 0.15-0.25 g samples of your cobalt compound into a 100 ml beaker. 

If there is no available salt of constant composition, such as copper(II) sulphate or iron(III), aluminium or chromium alums, it is advisable to prepare first a stock solution of an approximate concentration, slightly higher than required and to determine the concentration by a gravimetric or volumetric method. After suitable calculations the solution is diluted with pure solvent to obtain a solution containing exactly, e.g., 1 mg/ml of the given element. In some cases, standard solutions are obtained by dissolving a precisely weighed amount of the element in its pure form. 

Precisely weighed samples of 2 (ca. 2 mmol), or 4 (ca. 1 mmol), or 7 (1.00 mmol) were placed in a ball mill under argon together with the precise equivalent of la-c, or lb, or 6, respectively. The Teflon gasket was closed with... 

Phenylhydrazine (about 5 mmol precisely weighed) and the stoichiometric amount of the aldehyde la-f were rapidly mixed in a beaker at room temperature. The pure phenylhydrazone 2a-f quantitatively crystallized from the liquid with considerable heat production. The water of reaction was removed by evaporation in a vacuum for 1 h. 

Water standards generally consist of a precision-weighed mass of a solid hydrate of known composition oxalic acid at 2H2O (28.57 per cent in water), or tartrate of sodium at 2H2O (15.66 per cent in water). 

Your instructor will give you an unknown acid and tell you the mass of sample of unknown acid to weigh and the number of reactive protons per molecule. Record the proposed mass and the number of reactive protons per molecule in TABLE 25.IB. Carefully clean three 250- mL Erlenmeyer flasks. Weigh on an analytical balance, using weighing paper, three separate samples of your unknown, and record your masses in TABLE 25.IB. Quantitatively transfer each precisely weighed sample to the appropriately labeled Erlenmeyer flask. Add about 50. mL of distilled water and two drops of phenol-phthalein to each flask, and then titrate each solution with your standardized NaOH solution. (Use the identical procedure described for the standardization of NaOH solution in part A.) The unknown sample may not all go into solution when you add distilled water, but dissolution should be completed as you add NaOH solution. Record your titration data in TABLE 25.IB. 

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