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residue? What weight of residue should be obtained by heating 193 grammes of the salt?

672. By what reactions could you distinguish normal from common sodium phosphate, and both these salts from sodium meta- and pyrophosphates?

673. Solution of magnesium sulphate is added to sodium phosphate in presence of ammonia and ammoniuin chloride, what substance is precipitated ? What salt is obtained by igniting the precipitate ?

674. To what substance is the name glacial phosphoric acid” given, and how is it related to the orthophosphoric acid ?

675. Give a short account of the phosphates obtained by Fleitmann and Henneberg, and show how they are related to the other phosphates.

676. Give a short account of the different sulphides of phosphorus.

COMPOUNDS OF ARSENIC.

677. Who discovered hydride of arsenic (arsine), and how did he obtain it ? Give other methods.

678. What occurs when an electric current is passed through a solution of arsenious acid ? To what purpose has this reaction been applied by Bloxam ?

679. What occurs when arsine is (a) passed through a red-hot tube, (6) passed through solution of silver nitrate, (c) passed over sulphur exposed to sunlight, (a) passed over heated copper oxide ?

680. Give equations to express the reactions which occur when phosphine and arsine are separately led into solution of silver nitrate.

681. Describe the tests for arsenic known as Marsh's test” and “ Reinsch's test."

682. What occurs when arsine burns (a) in air, (6) in oxygen? How much oxygen is required for the complete combustion of 173 c.c. at N.T.P. ?

683. Express by equations the reactions which occur

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when arsine (a) is passed through solution of potassium permanganate, (6) is mixed with chlorine.

684. What is the formula of the only known chloride of arsenic, and how is the substance obtained ?

685. What is the action of arsenic chloride (a) on water, (b) on ammonia ?

686. In what different modifications does arsenic tri. oxide occur, and how may each be obtained ?'

687. What weight of the oxide is formed by burning 3.567 grammes arsenic in a current of oxygen?

688. How may arsenic trioxide be obtained in octahedral and in rhombic crystals ?

689. What molecular formula would you assign to arsenic trioxide knowing that its density is 13.85 (air I)?

690. How is arsenic pentoxide obtained, and what occurs when it is heated to a high temperature ?

691. What occurs when arsenic trioxide is heated in contact (a) with charcoal, (6) with acetates ?

692. Write the formula of the hydrides, chlorides, oxides, and acids of phosphorus and arsenic. In what respect do the pyro- and meta-acids of the two elements diller?

693. What is the action of arsenious acid on (a) chlorine, (6) iodine, (c) bleaching powder? Give equations for the reactions.

694. Ten grammes bleaching powder containing 34"7 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 ?

roo. 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.

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