693. What is the action of arsenious acid on (a) chlorine, (b) iodine, (c) bleaching powder? Give equations for the reactions.

694. Ten grammes bleaching powder containing 347 per cent. of available chlorine are dissolved in 1 litre of water. How much arsenic trioxide dissolved in potash will be required to saturate 100 c.c. of the bleaching powder solution?

695. What is the best antidote to arsenic poisoning? Explain its action.

696. What is Scheele's green, and how is it prepared on the large scale? What percentage of arsenic does

it contain?

697. How is arsenic acid obtained? By what tests is it distinguished from arsenious acid?

698. Give the formulæ of the silver and potassium salts of arsenious and arsenic acids.

699. How is the presence of arsenic ascertained in cases of poisoning, and how is the amount of the poison estimated?

700. Give a short account of the compounds of arsenic with sulphur and phosphorus. What is the composition of realgar and of orpiment?

COMPOUNDS OF SULPHUR.

701. Describe different methods for directly combining hydrogen with sulphur, and give the formula of the sulphide produced.

702. What volume of hydrogen at N.T.P. is required to combine with I gramme of sulphur?

703. How does sulphuretted hydrogen occur in nature, and how may its presence be detected?

704. How do you account for the occasional presence of sulphuretted hydrogen in the air?

705. Thorpe found that the mineral water at Harrogate contained 10:16 grains per gallon of sulphuretted hydrogen. How much iodine solution (containing o'005 gramme iodine in each cubic centimetre) must be added to a litre of this water, so as to decompose all the sulphuretted hydrogen?

706. A piece of sulphur is heated in contact with 39 c.c. of hydrogen at N.T.P. till combination takes place. Find the volume and weight of the sulphuretted hydrogen produced.

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, (b) 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, (b) sulphurous acid, (c) iodine, (d) ferric chloride, (e) silver nitrate, (f) ammonia, (g) lime, (h) sulphuric acid, (2) 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?

regard to its composition?

What views are held with

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 15° 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, (b) 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, (b) 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