Filter, folding

The filtration of any solution through the ordinary conical funnel may be hastened considerably by the use of a fluted filter-paper, instead of one folded into quarters in the usual way. The folding of a fluted paper may be learnt far more readily by a demonstration in the laboratory than by any written description. 

Proper procedure for filtering solids using filter paper. The filter paper circle in (a) is folded in half (b), and folded in half again (c). The filter paper is parted (d), and a small corner is torn off (e). The filter paper is opened up into a cone and placed in the funnel (f). Note that the torn corner is placed to the outside. 

Filtering is accomplished by folding the filter paper into a cone, which is then placed in a long-stem funnel (Figure 8.6). A seal between the filter cone and the... 

Like the photosynthetic reaction center and bacteriorhodopsin, the bacterial ion channel also has tilted transmembrane helices, two in each of the subunits of the homotetrameric molecule that has fourfold symmetry. These transmembrane helices line the central and inner parts of the channel but do not contribute to the remarkable 10,000-fold selectivity for K+ ions over Na+ ions. This crucial property of the channel is achieved through the narrow selectivity filter that is formed by loop regions from thefour subunits and lined by main-chain carbonyl oxygen atoms, to which dehydrated K ions bind. 

For purification, it is dissolved in 9-9.5 1. of boiling benzene (Note 4). The solution is filtered rapidly, using a 32-cm. folded filter in an 8-in. short-stem glass funnel. The recovery is 59-70 g. The fine, white crystals, which melt at 169-170° (Note 5), are stored in a brown glass bottle under nitrogen (Notes 6, 7, 8). 

The flask is again cooled in ice, the collected ether is returned to the reaction mixture, and the latter is decomposed by slowly adding first 85 ml. of ice water, then 400 ml. of ice-cold 10% hydrochloric acid. After stirring for some minutes, the contents of the flask are transferred to a separatory funnel. The layers are separated, and the ether layer is filtered through a folded filter and dried with calcium chloride (Note 8). 

Filter pack A filter medium uniformly folded and interleaved with spacers. 

A fluted filter is made by first folding a large circular filter paper in the 01 dinary way. It is then half opened out and the t vo quadrants folded towards the middle line (see a, Fig". 41), "This makes three creases with the hollows on the same side. TThe filter is now turned over and each section folded down the... 

The acid, without drying, is suspended in about 200 cc. of distilled water and with vigorous stirring, cautiously (Note 3) treated with 25 per cent sodium hydroxide solution until dissolved and the solution reacts neutral to litmus. The solution is then filtered through folded filter paper which should be free from soluble calcium salts, otherwise the filtrate will remain clouded by a suspension of the calcium salt. The clear, faintly yellow or colorless filtrate is then vigorously stirred and treated with 1.5 volumes of 95 per cent alcohol. Crystallization is induced by rubbing with a rod and then an additional volume of alcohol is added. The mixture should be allowed to cool to about 200 and stand for at least two hours to complete the precipitation of the salt, which is then filtered by suction and washed thoroughly with 85 per cent alcohol. The salt is then air-dried. The yield is 73-77 g. (38-40 per cent of the theoretical amount). 

Our journey begins with the photo-induced union of 3,4-dimethylfuran (19) and / -(benzyloxy)-propanal (18) (see Scheme 5). Irradiation of a solution of these two simple, achiral compounds in benzene with a 450 W Hanovia lamp equipped with a vycor filter results in the exclusive formation of head-to-head, exo photoadduct 17 in 63% yield. As a cw-fused dioxabicyclo[3.2.0]heptene system, intermediate 17 possesses a folded molecular framework to which access is obstructed on the concave face. In the presence of mCPBA, the less hindered convex face of the enol ether double bond is oxidized in a completely diastereoselective fashion, affording intermediate 16 in 80% yield after regioselective opening of... 

The size of the filter paper selected for a particular operation is determined by the bulk of the precipitate, and not by the volume of the liquid to be filtered. The entire precipitate should occupy about a third of the capacity of the filter at the end of the filtration. The funnel should match the filter paper in size the folded paper should extend to within 1-2 cm of the top of the funnel, but never closer than 1 cm. 

With the exception of iron(II) and uranium(IV), the reduced solutions are extremely unstable and readily re-oxidise upon exposure to air. They are best stabilised in a five-fold excess of a solution of 150g of ammonium iron(III) sulphate and 150 mL of concentrated sulphuric acid per litre [approximately 0.3M with respect to iron] contained in the filter flask. The iron(II) formed is then titrated with a standard solution of a suitable oxidising agent. Titanium and chromium are completely oxidised and produce an equivalent amount of iron(II) sulphate molybdenum is re-oxidised to the Mo(V) (red) stage, which is fairly stable in air, and complete oxidation is effected by the permanganate, but the net result is the same, viz. Mo(III)- Mo(VI) vanadium is re-oxidised to the V(IV), condition, which is stable in air, and the final oxidation is completed by slow titration with potassium permanganate solution or with cerium(IV) sulphate solution. 

Zirconium ( > 100 mg in ca /. M sulphuric acid solution). Add freshly prepared 10 per cent aqueous diammonium hydrogenphosphate solution in 50-100-fold excess. Dilute to 300 mL, boil for a few minutes, allow to digest on a water bath for 15-30 minutes and cool to about 60 °C. Filter through a quantitative filter paper, wash first with 150 mL of 1M sulphuric acid containing 2.5 g diammonium hydrogenphosphate and then with cold 5 per cent ammonium nitrate solution until the filtrate is sulphate-free. Dry the filter paper and precipitate at 110°C, place in a platinum crucible and carefully burn off the filter paper. Finally heat at 1000 °C for 1-3 hours and weigh as ZrP207 (Section 11.51). 

No. 41 or 541 filter paper. Wash the precipitate first with warm, dilute hydrochloric acid (approx. 0.5M), and then with hot water until free from chlorides. Pour the filtrate and washings into the original dish, evaporate to dryness on the steam bath, and heat in an air oven at 100-110 °C for 1 hour. Moisten the residue with 5 mL concentrated hydrochloric acid, add 75 mL water, warm to extract soluble salts, and filter through a fresh, but smaller, filter paper. Wash with warm dilute hydrochloric acid (approx. 0.1M), and finally with a little hot water. Fold up the moist filters, and place them in a weighed platinum crucible. Dry the paper with a small flame, char the paper, and burn off the carbon over a low flame take care that none of the fine powder is blown away. When all the carbon has been oxidised, cover the crucible, and heat for an hour at the full temperature of a Meker-type burner in order to complete the dehydration. Allow to cool in a desiccator, and weigh. Repeat the ignition, etc., until the weight is constant. 

Fick s law 592 Filter funnel 102 Filter papers 115 folding of, 116 incineration of, 120, 121 macerated, 450 quantitative, (T) 116 Filter pulp 450 Filtering crucibles 102 Filters, optical 661 Filtration 102, 106, 115 accelerated, 450 technique of, 116, 117 with filter papers, 116 with filtering crucibles, 117 Flame emission spectroscopy 779, 797 background correction, 795 elementary theory of, 780 D. of alkali metals by, 812... 

Dimethyl octanedioate (dimethyl suberate), 71.2 g (0.352 mol), 1,4-butanediol (5% excess 0.370 mol, 33.3 g), and 0.02 g of tetraisopropoxytitanium (0.025% of final polyester mass) are placed in a three-necked round-bottomed flask fitted with a mechanical stirrer. The medium is slowly heated to 150°C within 4 h under nitrogen atmosphere while methanol is distilled off. Vacuum is then slowly applied and the reaction continued at 0.01 mbar and 150°C for 48 h. The resulting polyester is cooled down, dissolved in chloroform (50 g polyester/200 mL chloroform), and slowly added to a 10-fold volume of methanol under high-speed agitation (1000 rpm). The precipitated polyester is filtered off and dried at 30°C under vacuum (0.1 mbar). 

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