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511. Express by equations the action of (a) water on boron fluoride, (6) heat on potassium borofluoride.

512. What is the formula of boric anhydride? What acid is formed by its union with water ?

513. What loss of weight would 2*189 grammes of boric acid suffer if heated till free from water ?

514. How does boric acid occur in nature, and how is the pure

acid obtained from the natural source ? 515. What is borax, and how is boric acid obtained from it? How is the presence of boric acid in a mixture ascertained ?

516. Draw graphic formula for boric and metaboric acids, also for boron trioxide, and state how the first must be treated so as to yield the others.

517. How may boron be combined with nitrogen ano with sulphur? Describe the two products and give their formulæ.

COMPOUNDS OF CARBON.

518. What bodies are called hydrocarbons? Give the names and formulæ of a few.

519. Name the chief hydrocarbons contained in coalgas. To what does it owe its illuminating power ?

520. How is coal-gas made and purified ? Give a short account of its discovery and introduction as a source of light.

521. Name the chief products obtained by the destructive distillation of cannel coal, and state how the coal-gas is separated from the others.

522. Name all the elements usually present in coalgas, and state how they are supposed to be combined.

523. A sample of Wigan cannel coal contains 5'71 per cent. hydrogen. If coal-gas made from this contained all the hydrogen as marsh-gas, find the volume of the latter which should be obtained from a kilogramme of the coal,

524. A sample of coal-gas contains in 100 volumes 45°58 hydrogen, 34'90 marsh-gas, 664 carbonic oxide. Find the volume and weight of carbon dioxide and water produced when a litre of it is burned.

525. What compounds are given off when a paraffin candle and coal-gas are separately burned in air ?

526. Explain the construction of a Bunsen lamp. Why does the flame not blacken a cold porcelain plate held

over it ?

527. A soap bubble inflated with coal-gas is allowed to ascend through the air into a bell-jar filled with hydrogen. What occurs when it reaches the hydrogen ?

528. Explain the principle and construction of the Davy lamp.

529. Describe experiments which show that the inner portion of a candle or gas-flame contains unburnt gases.

530. How may carbon be directly combined (a) with hydrogen, (6) with oxygen ?

531. Give various methods for the preparation of carbon monoxide. Represent the reactions by equa-' tions.

532. What weight of crystallized oxalic acid is needed

to furnish 17 grammes of carbon monoxide, and what volume of carbon dioxide at N.T.P. would be likewise obtained ?

533. How may carbon monoxide be obtained from carbon dioxide, and vice versâ ?

534. Explain the production of carbon monoxide when coals burn in an ordinary fireplace.

535. How may carbon dioxide be separated from carbon monoxide and vice versa?

536. One gramme of carbon is heated in contact with 119 litres of carbon dioxide at N.T.P. What reaction occurs, and what is the volume after the experiment ?

537. You are required to prepare (a) pure carbon dioxide, (6) pure carbon monoxide, using only carbon and oxygen. How will you proceed in each case ?

538. What volume of oxygen when exploded with 120 C.c. carbon monoxide is just sufficient to combine with it, and what volume of carbon dioxide is produced ?

539. What weight of carbon is contained (a) in a litre of carbon monoxide, (6) in a litre of carbon dioxide, and how could you obtain it from each gas?

540. Give two distinct ways for obtaining carbon dioxide from marble (carbonate of lime), and describe the properties of the gas.

541. What occurs when carbon dioxide is (a) heated with potassium, (6) shaken up with litmus solution, (c) allowed to pass through solution of caustic potash ?

542. What is lime-water, and how is it made? What happens when carbon dioxide is led into it (a) in small quantity, (b) in excess ? Express all the reactions by equations.

543. How is carbon dioxide obtained as a liquid and as a solid ?

544. Explain the term temporary hardness” applied to water. What occurs when such water is boiled ?

545. A diamond weighing oʻ1247 gramme and containing o'o3 per cent. of ash is burned in oxygen. Find the volume and weight of carbon dioxide produced.

546. A closed room has a capacity of 27 cubic metres. Find the weight of oxygen, nitrogen, and carbon dioxide it contains, before and after a kilogranıme of pure carbon is burned in it.

547. Dumas and Stas found that 300'02 parts of diamond combine with 800 parts of oxygen to form

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