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707. How is sulphuretted hydrogen usually prepared ? What is it chiefly used for in the laboratory ?

708. What impurities are present in sulphuretted hydrogen prepared in the ordinary way? How may it be obtained (a) in a purer form, (6) perfectly pure ?

709. Mention various methods for obtaining sulphur from sulphuretted hydrogen, and state how the gas may be decomposed into hydrogen and sulphur,

710. How may the composition of sulphuretted hydrogen be ascertained ?

711. Sulphuretted hydrogen is added to each of the following bodies, state fully what occurs in each case, and give equations for the reactions-(a) chlorine, (6) sulphurous acid, (c) iodine, (d) ferric chloride, (e) silver nitrate, (s) ammonia, (g) lime, (h) sulphuric acid, (i) nitric acid, (j) antimony trichloride, (k) zinc chloride.

712. A litre of sulphuretted hydrogen is burned in air. Find the volumes of the products at N.T.P., and of the air required for its combustion.

713. What occurs when a mixture of sulphur and paraffin is heated ?

714. How may the formation of sulphur dioxide by the combustion of sulphuretted hydrogen in air be demonstrated ?

715. How did Faraday obtain sulphuretted hydrogen in the liquid state ? Describe better methods for effecting this result.

716. How is hydrogen persulphide obtained, and what are its properties? What views are held with regard to its composition ?

717. Compare the sulphides of hydrogen with the oxides of hydrogen, and point out their analogies.

718. What substance is formed by allowing chlorine to pass over heated sulphur ? When the well-cooled product is further treated with chlorine what compound results ?

719. How is sulphur tetrachloride obtained ? What compounds of sulphur with bromine and iodine have been obtained ?

720. When oxygen is passed over heated sulphur, what gaseous compound is formed ? If the two gases were passed over finely divided platinum, what compound would result?

721. Sulphur is heated in contact with 173 c.c. of oxygen (at a temperature of 15o C. and under a pressure of 753 m.m.) till combination takes place. Find the volume of the compound produced, and the weight of sulphur contained in it.

722. How may sulphur dioxide be obtained (a) from sulphuric acid, (6) from sodium sulphite? How may the gas be liquefied ?

723. Give the volume at N.T.P. of each of the gases obtained by heating 489 grammes of charcoal with sulphuric acid.

724. What occurs when sulphuric acid is dropped on red-hot platinum? What quantity of sulphuric acid would yield in this way 1297 c.c. of oxygen gas ?

725. Express by equations the reactions which occur when strong sulphuric acid is heated with (a) mercury, (6) sulphur, (c) copper.

726. What is the action of each of the following bodies on sulphur dioxide ? (a) lead dioxide, (b) water, (c) hydrogen dioxide, (d) nitric acid.

727. Give different methods for preparing sulphur trioxide, also a short account of its properties, and state what occurs when it is passed through a redhot tube.

728. How is sulphur sesquioxide obtained, and what

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occurs when it is heated and when it is added to water ?

729. Give the names and formulæ of all oxyacids of sulphur.

730. What acid body is obtained by the action of zinc on sulphurous acid ? What name was given to it at first, and what is its more systematic name?

731. By what reactions would you distinguish sulphurous acid from Schützenberger's acid ?

732. How would you prepare a solution of sulphurous acid in water ? Why can the acid not be obtained except in solution ?

733. What occurs when an aqueous solution of sulphurous acid is (a) exposed to air, (6) added to infusion of rose leaves, (c) mixed with chlorine water?

734. How does sulphurous acid act as a bleaching agent ? Compare its bleaching action with that of chlorine. Give equations.

735. What is the action of solution of iodine sulphurous acid in dilute and in strong solutions ? Express the reactions by equations.

736. If 432 c.c. of iodine solution (containing o'c05 gramme iodine in each c.c.) were added to a solution

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of sulphurous acid (containing a little starch) before a blue colour appeared, how much sulphur dioxide was in solution ?

737. Express by equations the reactions which occur when hydrochloric acid is added to (a) sodium sulphite, (6) sodium thiosulphate.

738. What is the action of sulphur dioxide on iodic acid, and how may the reaction be used as a test for the gas?

739. What is meant by an "antichlor" ? Explain the use of sulphur dioxide as an antichlor.

740. What occurs when sodium sulphite is digested with sulphur? Give the formula of the body produced, and show how it is related to sulphite and sulphate of sodium.

741. What reaction occurs when sodium sulphite is treated with zinc and a dilute acid ?

742. How is sodium thiosulphate made on the large scale, and what is it used for in photography ?

743. Give all the reactions by which you could distinguish a sulphite from a thiosulphate.

744. What occurs when a solution of iodine is added to a solution of sodium thiosulphate? Name all the

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