Sieve shaking

A cloud of zinc dust generated by sieving the hot dried material exploded violently, apparently after initiation by a spark from the percussive sieve-shaking mechanism... 

Wet Method. Transfer a dried and weighed portion of approx lOg of the sample to a 149-micron (No 100) US Std sieve which has been placed in a porcelain evaporating dish containing sufficient water to cover the wire portion of the sieve. Shake the sieve for 10 mins in such a manner that the Hg fulminate is below the surface of the water and any material passing thtu the sieve is caught on the evaporating dish. Transfer the portion of the fulminate retained on the sieve to a tared filter paper and wash twice with alcohol and once with ether. 

A cloud of zinc dust generated by sieving the hot dried material exploded violently, apparently after initiation by a spark from the percussive sieve-shaking mechanism [1]. Precautions recommended include use of cold zinc and total enclosure of such processes [2]. The possibility of explosions of zinc dust suspended in air is presented as a serious hazard [3]. A serious dust explosion in the air filter unit of a zinc grinding mill was initiated by a spark from an explosion relief panel [4]. 

Transfer the nest of sieves to the drum of the sieve. Shake and clamp them in position. Then fill the drum with salt free water upto a level, slightly below the top screen, when the sieves are in highest position. 

The main factors that affect the particle passage through sieve aperture are the method of sieve shaking, the ratio of open area of sieve to total area, particle size distribution, the number of particles on the sieve (sieve loading), and the dimension and shape of the particle. Friability and cohesiveness of solid particles can also affect the sieving operation. Difficulty can also arise with high aspect ratio particles (i.e., needle-shaped or flaky particles). 

Rotap. Testing sieve shaking equipment (C-E Tyler Co, Mentor, Ohio). 

Ketones are more stable to oxidation than aldehydes and can be purified from oxidisable impurities by refluxing with potassium permanganate until the colour persists, followed by shaking with sodium carbonate (to remove acidic impurities) and distilling. Traces of water can be removed with type 4A Linde molecular sieves. Ketones which are solids can be purified by crystallisation from alcohol, toluene, or petroleum ether, and are usually sufficiently volatile for sublimation in vacuum. Ketones can be further purified via their bisulfite, semicarbazone or oxime derivatives (vide supra). The bisulfite addition compounds are formed only by aldehydes and methyl ketones but they are readily hydrolysed in dilute acid or alkali. 

The sieving operation starts by mounting the sieves in a nest, the coarsest at the top. The sample is placed on the top screen, and the screens are shaken for several minutes. It is generally impossible to screen a sample completely the longer one shakes the screens, the more material comes thru, although to a continu-... 

It was concluded that approximately three minutes sieving time was adequate with the air-jet sieve even with waxlike materials such as cadmium stearate whereas, 20 minutes or longer was required for vibrating or shaking screens. The data presented (Refs 19 35) for AP by the Alpine, Tyler Ro-Tap, and Micromerograph agree remarkably well... 

Sieving Time Because sieving time depends upon the type of sieving motion and the provision for continuous movement of the sample over all parts of the sieving surface, the only requirement for sieving time appears to be that shaking be continued until equilibrium conditions are reached... 

Diehloromethane is purified by shaking with concentrated sulfuric acid, washing with aqueous sodium bicarbonate and water, drying over anhydrous calcium chloride, and distilling. The purified solvent is stored in the dark over 4A molecular sieves. 

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