Crucibles, evaporator

Ash Content shall be not greater than 0.005% Transfer a lOg portion of sample into an accurately tared porcelain crucible, evaporate to dryness on a hot plate, and ignite the residue... 

Step 2a. In at least triplicate, pipette exactly 5.0 mL of the carrier solution to a clean weighed porcelain crucible. Evaporate the solution carefully to dryness and ignite the residue in a muffle furnace at 1000 °C for 1 hour. 

Crucible, evaporation A container for holding molten material. See also Skull. 

Noack volatility (lubricants) T 60-161 Weight of a crucible before and after evaporation... 

Transfer the filtrate to a ceramic evaporating dish and heat on a water bath until a crystalline scum forms on the top. Cool the dish quickly then filter the mess on the vacuum Buchner to yield 96g of Methylamine Hydrochloride. Concentrate the filtrate once again to obtain a second crop of crystals, -IQg. Concentrate the filtrate a third time as far as possible using the water bath, then store the dish in a vacuum dessicator loaded with Sodium Hydroxide in the bottom for 24 hours. Add Chloroform to the residue left in the crucible to dissolve out Dimethylamine Hydrochloride (distill off the Chloroform to recover - good stuff) then filter on the venerable old vacuum Buchner funnel to yield an additional 20g of Methylamine Hydrochloride, washing the crystals in the funnel with a small poiiion of Chloroform ( 10mL). 

Porcelain crucibles are very frequently utilised for igniting precipitates and heating small quantities of solids because of their cheapness and their ability to withstand high temperatures without appreciable change. Some reactions, such as fusion with sodium carbonate or other alkaline substances, and also evaporations with hydrofluoric acid, cannot be carried out in porcelain crucibles owing to the resultant chemical attack. A slight attack of the porcelain also takes place with pyrosulphate fusions. 

Silver apparatus. The chief uses of silver crucibles and dishes in the laboratory are in the evaporation of alkaline solutions and for fusions with caustic alkalis in the latter case, the silver is slightly attacked. Gold vessels (m.p. 1050 °C) are more resistant than silver to fused alkalis. Silver melts at 960 °C, and care should therefore be taken when it is heated over a bare flame. 

Infrared lamps and heaters. Infrared lamps with internal reflectors are available commercially and are valuable for evaporating solutions. The lamp may be mounted immediately above the liquid to be heated the evaporation takes place rapidly, without spattering and also without creeping. Units are obtainable which permit the application of heat to both the top and bottom of a number of crucibles, dishes, etc., at the same time this assembly can char filter papers in the crucibles quite rapidly, and the filter paper does not catch fire. 

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. 

To determine the exact Si02 content of the residue, moisten it with 1 mL water, add two or three drops of concentrated sulphuric acid and about 5 mL of the purest available hydrofluoric acid. (CARE ) Place the crucible in an air bath (Section 3.21) and evaporate the hydrofluoric acid in a fume cupboard (hood) with a small flame until the acid is completely expelled the liquid should not be boiled. (The crucible may also be directly heated with a small non-luminous flame.) Then increase the heat to volatilise the sulphuric acid, and finally heat with a Meker-type burner for 15 minutes. Allow to cool in a desiccator and weigh. Re-heat to constant weight. The loss in weight represents the weight of the silica (Note 2). 

Crucibles for aluminum evaporation and for molecular beam epitaxy. 

Borides are generally resistant to molten metals, at least to those that do not readily form borides, such as copper, zinc, magnesium, aluminum, tin, lead, and bismuth. TiB2 is especially resistant to molten aluminum and, as such, is used in crucibles for evaporation of the metal. 

In a typical reaction 100 - 200 mg of metal [Cr or Ni] was evaporated from a preformed alumina crucible over a period of 60 - 90 min and deposited into a mixture of 2 in poly(dimethylsiloxane) [Petrarch Systems 0.1 P.] within a rotary solution metal vapor reactor operating at 10 4 torr. The reaction flask was cooled to approximately 270 K by an iced-water bath. For a description of the apparatus see Chapter 3 of reference 4. The product in each case was a dark orange viscous liquid and was characterized as obtained from the reaction vessel. 

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