carbon dioxide.

Calculate from these data the com

bining weight of carbon.

548. What are petrefactions, and how have they been formed?

549. What is the formula for carbonic acid? What occurs when its aqueous solution is (a) boiled, (b) added to litmus solution, (c) added to lime water?

550. How did Faraday first obtain carbon dioxide in the liquid state? What is meant by the "critical point " of a gas? How did Andrews ascertain the critical point of carbon dioxide?

551. How does liquid carbon dioxide occur in nature, and how has this been ascertained?

552. A piece of Iceland spar lost when heated 1.236 gramme. Find its weight, and the volume of carbon dioxide evolved, measured at 13° C. and 755 m.m. pressure.

553. How may carbon be combined with sulphur, and what are the properties of the product?

554. How much carbon and sulphur are contained in a litre of carbon disulphide (S. G. = I 1292), and how could they be obtained from it?

COMPOUNDS OF SILICON.

555. How did Buff and Wöhler first obtain silicon hydride? How may the substance be obtained in the pure state?.

556. What are the properties of silicon hydride, and how is it most readily prepared?

557. How is silicon tetrachloride prepared, and what is its action on water?

558. Represent by an equation the reaction which occurs when a mixture of silica and fluor spar is heated with sulphuric acid. What happens when the product is passed into water?

559. Name six forms of silica found in nature, and state the composition of the following bodies-felspar, opal, clay, serpentine, garnet, talc, orthoclase, and agate.

560. In what organic bodies does silica occur, and how may its presence in water be ascertained?

561. Suggest a process for obtaining oxygen from silica.

562. What are zeolites, and what is the action of hydrochloric acid on them?

563. What is the action (if any) on silica of (a) sulphuric acid, (b) potash, (c) hydrofluoric acid, (d) sodium carbonate (heated till fused), (e) chlorine ?

564. How is the quantity of silica in a sample of water usually determined?

565. How would you make a complete, quantitative analysis of potash felspar?

566. Describe Graham's researches which resulted in the discovery of ortho-silicic acid.

567. What is the substance termed soluble glass, and what is the action of hydrochloric acid on a strong and on a weak solution of it?

568. Explain the term " dialysis," "colloids," "crystalloids." Classify the following substances into colloids and crystalloids-common salt, sugar, starch, arsenious acid, glue, nitre, and gum.

COMPOUNDS OF NITROGEN.

569. Give a short account of the history and natural occurrence of ammonia.

570. How may ammonia be prepared (a) by synthesis, (b) from nitric acid, (c) from ammonium salts?

571. What is the chief commercial source of ammonia compounds? Describe fully the preparation of salammoniac on the large scale.

572. Represent by equations the action of potash and of quick-lime on ammonium chloride. How much quick-lime is necessary to decompose 147 grammes of ammonium chloride?

573. A litre of ammonia gas at N.T.P. weighs 07619 gramme. Find how much heavier it is than hydrogen, and how much lighter than air.

574. How was ammonia gas first liquefied by Faraday? Describe Carré's apparatus for obtaining ice artificially by means of liquid ammonia.

575. Is ammonia a combustible gas? Describe experiments in support of your answer.

576. What occurs when ammonia gas is passed (a) over heated potassium, (b) into hydrochloric acid, (c) over red-hot fragments of porcelain?

577. One gramme of water at 14° C. and under a pressure of 760 m.m. absorbs 0612 gramme ammonia. What weight of ammonium chloride and of lime must be heated to saturate with ammonia a kilogramme of water at the same temperature and pressure?

578. Electric sparks are passed through 79 c.c. of ammonia gas. What change in volume occurs, and what is the composition by volume of the residue?

579. What volume of ammonia gas at N.T.P. should be obtained by heating 139 grammes ammonium chloride with quick-lime?

580. What is the weight of 35 litres ammonia gas at N.T.P.? When 35 litres of hydrochloric acid gas are mixed with it, what occurs, and what is the weight of the product?

581. Under what circumstances does ammonia burn, and what are the products of combustion? Find the