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494. What is the action of sulphuric acid on calcium Nuoride, and of heat on hydrogen potassium fluoride ? Give equations.

495. What is the difference between the action of anhydrous and dilute hydrofluoric acid on (a) glass, (69 gutta-percha ?

496. What is the action of hydrofluoric acid on silica and of the product on water? State also the action of the acid on glass. Give equations.

497. A weighed piece of glass is acted on by hydrofluoric acid. After the action it is found to have lost 1'347 gramme, how much hydrofluoric acid is needed to produce this result?

498. Gore heated 16-4 grains silver fluoride in contact with 6 cubic inches pure hydrogen and obtained 14.5 cubic inches hydrofluoric acid measured at 200° F. Find the volume of hydrogen which had combined


with fluorine, and state what conclusions you draw as to the composition and density of hydrofluoric acid.

499. 4'387 grammes meerschaum (SizO10H Mg2) are heated with hydrofluoric acid till no further reaction

How much silicon tetrafluoride should be formed ?

500. How is hydrofluoric acid used in the preparation of eudiometers ?

501. How would you obtain the fluorides of silver, barium, and potassium ? Which of these salts dissolves in water?

502. Give the formulæ of potassium borofluoride and of potassium silicofluoride, and state how each of these substances is obtained.

503. How is hydrofluosilicic acid prepared ? Sketch the apparatus required for its preparation, and give its action on solutions of potassium and barium salts.


504. How is boron hydride prepared ? What are its properties, and what occurs when it burns in air ?

505. Compare the properties of boron hydride with those of the hydrides of silicon, phosphorus, and arsenic.

506. How may the composition of boron hydride be ascertained ?

507. How is the chloride of boron prepared, and what is its formula ? What is its action when heated with (a) sodium, (6) magnesium, (c) zinc ?

508. What occurs when boron trichloride is placed in water ? Give an equation and name another chloride which reacts similarly on water.

509. A compound of boron trichloride with ammonia contains 14068 per cent. of nitrogen, find its formula and state how it is obtained.

510. Give the formulæ and modes of preparation of the compounds of boron with bromine and fluorine.

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 gramines 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 formulæ 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.



518. What bodies are called hydrocarbons? Give the names and formulæ of a few. 519. Name the chief hydrocarbons contained in coal

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,

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