Operations weighing

Detectable concentration ranges are mbe-dependent and can be anywhere from one-hundredth to several thousand ppm. The limits of detection depend on the particular detector mbe. Accuracy ranges vary with each detector mbe. The pump may be handheld during operation (weighing from 8 to 11 ounces), or it may be an automatic type (weighing about 4 pounds) which collects a sample using a preset number of pump strokes. 

Microchemistiy - a branch of analytical chemistry that involves procedures that require handling of very small quantities of materials. Specifically it refers to carrying out various chemical operations (weighing, purification, quantitative and qualitative analysis) on samples ranging from 0.1 to 10 milligrams. (The Condensed Chemical Dictionary 1971). 

A powder exhaust unit for most dust releasing operations weighing, capsule filling, mixing of solids, rotor-stator mixing... 

The operator weighs his beliefs according to the evidence available to him. If the computer system indicates a closed valve and if he sees that the lever is on the closed position, he has evidence to support the belief that no leak will occur during his watch. However, he lacks knowledge about the maintenance performed on the valve. In line with statement (b), this implies that the operator is in a state of evidential uncertainty because the maintenance clearly has a relation to the possibility of a leak. 

For onshore operations various types of landrigs are available, ranging from truck mounted light rigs to heavy landrigs weighing several hundred tons. 

This operation of weighing out the sample of substance to be analysed may conveniently be carried out while waiting for the absorption tubes to mature after polishing. 

Method 1. From ammonium chloroplatinate. Place 3 0 g. of ammonium chloroplatinate and 30 g. of A.R. sodium nitrate (1) in Pyrex beaker or porcelain casserole and heat gently at first until the rapid evolution of gas slackens, and then more strongly until a temperature of about 300° is reached. This operation occupies about 15 minutes, and there is no spattering. Maintain the fluid mass at 500-530° for 30 minutes, and allow the mixture to cool. Treat the sohd mass with 50 ml. of water. The brown precipitate of platinum oxide (PtOj.HjO) settles to the bottom. Wash it once or twice by decantation, filter througha hardened filter paper on a Gooch crucible, and wash on the filter until practically free from nitrates. Stop the washing process immediately the precipitate tends to become colloidal (2) traces of sodium nitrate do not affect the efficiency of the catalyst. Dry the oxide in a desiccator, and weigh out portions of the dried material as required. 

Scale of Operation The scale of operation for precipitation gravimetry is governed by the sensitivity of the balance and the availability of sample. To achieve an accuracy of 0.1% using an analytical balance with a sensitivity of 0.1 mg, the precipitate must weigh at least 100 mg. As a consequence, precipitation gravimetry is usually limited to major or minor analytes, and macro or meso samples (see Figure 3.6 in Chapter 3). The analysis of trace level analytes or micro samples usually requires a microanalytical balance. 

Weighing is the operation of determining the mass of any material as represented by one or more objects or by a quantity of bulk material. Proportioning is the control, by weighing, of relative quantities of two or more ingredients according to a specific recipe in order to make a mixed product, or to prepare the ingredients for use in a chemical process. 

The load-receiving element supports the load during the weighing operation. It may take the form of a scoop, platter, deck, rad, hopper, belt... 

Buoyant Effect of Air. Weighing operations performed m vacuo are not affected by buoyancy forces. An object in air, however, is subject to a buoyancy force that is equal and opposite to the gravitational force on the mass of air the object displaces (10). If the equal arm balance of Figure 1 is in balance with a test weight of mass, in one pan, and material of mass, m, in the other, m = m if they have the same density. If the densities are different, then the buoyancy forces acting on each pan affect the result. Taking moments about the center pivot point gives... 

Scales are available in a variety of designs and configurations to faciHtate different weighing operations (7). The two principal categories are industrial and retail scales, and precision scales and balances. 

Precision bench scales are designed for use in industrial settings they typically have capacities below 50 kg and 30,000 or more displayed divisions. Typical apphcations are counting very small parts or weighing hand-add materials for proportioning operations. 

---