Crucible cover

Place about 01 g. of the compound in a porcelain crucible or crucible cover. Heat it gently at first and finally to dull redness. Observe ... 

A mixture of 1 c.c. of beoxaldebyde and 5 grams of lime are placed iu the bottom of a platinum cruoibls about 0 ius. in depth, a layer of lime placed OQ the cop and the crucible covered and gently heated a oou-eiderabls escape of betizaldehyde takes place, so that it is obvious that the results can have no quantitative valne. 

Schmelztiegel, m. crucible, melting pot. -deckel, m. crucible cover (Metal.) tile, -halter, m. crucible holder, crucible support, -zange, /. crucible tongs. 

A process for the gravimetric determination of mixtures of selenium and tellurium is also described. Selenium and tellurium occur in practice either as the impure elements or as selenides or tellurides. They may be brought into solution by mixing intimately with 2 parts of sodium carbonate and 1 part of potassium nitrate in a nickel crucible, covering with a layer of the mixture, and then heating gradually to fusion. The cold melt is extracted with water, and filtered. The elements are then determined in the filtrate. 

The normality of the stronger solution is checked once a month in the following way 0.1 ml ethyl hydroperoxide solution +2 ml potassium iodide (20 g/100 ml) + 2 chops of glacial acetic add are placed in a porcelain crucible, covered with a lid, and allowed to stand at room temperature for 4 hours. The amount of iodine released is then titrated with 0.05 N sodium thiosulfate. 

B. Moisture driven from the hydrate condensed on the inside of the crucible cover before the student weighed the anhydride. 

For complete drying of the charcoal, put it into an iron crucible, cover it with a lid, and roast it during 20-30 min at 500 °C. Cool it in a desiccator. What is the essence of the carbon activation process ... 

Preparation of Anhydrous Chromium(III) Chloride. Perform the experiment in a fume cupboard Grind 5 g of charcoal into a fine powder in a mortar, mix it with 12.5 g of chromium(III) oxide, add a thick starch size or a dextrin solution in cold water, and make beads about 5 mm in diameter from the mixture. Put the beads onto a clay dish and dry them in a drying cabinet at 110-120 °C. Next put them into an iron crucible, cover them with the charcoal powder and a lid, and roast them. 

Preparation of Lead. a. Thoroughly mix 5 g of lead(II) oxide and 0.5 g of finely ground charcoal. The lead(II) oxide must be preliminarily dried in a drying cabinet at 100 °C, and the charcoal roasted in an iron crucible covered with a lid. Put the mixture into a porcelain crucible, spill charcoal over it, and roast it in a muffle furnace at 800 °C. After 10 or 15 minutes, mix the contents of the crucible with a carbon rod and again roast them during 30 minutes. Pour out the molten lead onto a chamotte dish. Cool the metal bead and keep it for following experiments. Calculate the yield in per cent. Write the equations of the reactions. 

Ignition test. Place 0.1-0.2 g of the mixture on a porcelain crucible cover heat gently at first over a small flame and finally ignite strongly. Observe ... 

Ignition test Place 0.1 g-0.2g of the mixture upon a porcelain crucible cover or upon a piece of platinum foil heat gently at first and finally ignite strongly. Note ... 

Place the crucible in a clay triangle, which is mounted on an iron ring and attached to a ring stand. Be sure the crucible is firmly in place in the triangle. Place the crucible cover on the crucible slightly ajar (Fig. 7.1a). 

Allow the crucible assembly to cool to room temperature. Weigh the cool crucible, cover, and magnesium oxide to 0.001 g (5). 

The excess phosphorus condenses in the yellow form on the cover and in the upper part of the crucible. When the crucible cover is removed, the excess phosphorus burns. As soon as the burning of the phosphorus has subsided somewhat, the crucible is placed in a desiccator. The phosphide appears as a dark-colored, rather fluffy mass. Usually, there is little difficulty in preventing contamination from the excess phosphorus and its oxide, since they tend to stick to the crucible and its cover. The ash of the magnesium is easily picked out. The product is then loosened with a spatula and removed from the crucible. 

Sodium Oxide and Water. Support a porcelain crucible cover on a triangle and heat it to redness while it is thus hot, place upon it, by means of iron pincers, a piece of sodium the size of a small pea. Remove the burner and let the sodium bum. When cold dissolve the white oxide in a few cubic centimeters of water and test the solution with litmus. Notice some effervescence when the oxide is dissolving. Note that the solution turns litmus blue and feels very slippery when rubbed between the fingers. 

Place a few small lumps of marble (calcium carbonate) in a small porcelain crucible. Cover the crucible in order to keep in the heat, and heat it strongly for 20 minutes with a Bunsen flame. When the product has cooled, wet each lump with a single drop or two of water and wait a few minutes, if necessary, to observe the effect. The lumps should grow very hot, and steam be driven off. Then wet the product with somewhat more water, and test the reaction of the moist mass towards litmus. The litmus is colored strongly blue by the suspension. 

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