451. What occurs when perchloric acid is added to (a) water, (b) charcoal ?

452. Calculate the composition of potassium perchlorate from the following experimental data obtained by Roscoe. o'9915 gramme of the pure salt lost on heating 0'4570 gramme, the residue required o'7683 gramme of silver for complete precipitation. Also, o'3165 gramme of the salt when treated with sulphuric acid yielded 0'201 gramme potassium sulphate.

453. How could you distinguish (a) a solution of chlorine from one of hypochlorous acid, (b) a solution of potassium chlorate from one of potassium perchlorate?

454 What quantities respectively of potassium chlorate and potassium perchlorate would be needed to furnish when heated a litre of oxygen at N.T.P.?

455. Starting with potassium chlorate, how could you obtain the chloiates of sodium and barium?

COMPOUNDS OF BROMINE.

456. Describe different methods for combining bromine directly with hydrogen.

457. What weight of bromine and of hydrogen does a litre of hydrobromic acid gas at N.T.P. contain?

458. What happens when potassium bromide is dropped into (a) sulphuric acid, (b) phosphoric acid?

459. Express by equations the action of hydrobromic acid on sulphuric acid, and of bromine water on sulphuretted hydrogen.

460. If a hydrogen flame be surrounded with bromine vapour what occurs? If coal-gas be substituted for hydrogen what occurs?

461. What is the action of phosphorus on chlorine, on bromine, and on iodine, and what is the action of water on each of the products?

462. Describe fully how you would fill a cylinder with ́

dry hydrobromic acid, and how you would show that it is soluble in water and acid.

463. A cylinder standing over mercury is half filled with sulphuretted hydrogen; a thin glass bulb containing bromine is passed up and then broken in the gas, What reaction occurs, and how does it affect the volume of gas in the cylinder?

464. How may the composition of hydrobromic acid be ascertained?

465. Express by equations the reactions which occur when hydrobromic acid is added to (a) zinc, (b) silver nitrate, (c) chlorine, (d) manganese dioxide.

466. Aqueous solution of hydrobromic acid having a specific gravity of 1515 has been found to contain 49°8 per cent. of the gas. How much silver nitrate is needed to precipitate 100 c.c. of the solution?

467. Do chlorine and bromine unite together? How could you distinguish between a solution of chlorine in bromine and a compound of the two elements?

468. No compound of bromine with oxygen is at present known. Suggest methods for attempting to prepare such a compound.

469. Give different methods for the preparation of

hypobromous acid. How would you distinguish it from hypochlorous acid?

470. What occurs when bromine is left in contact with slaked lime, and what is the action of (a) hydrochloric acid, (b) nitric acid, on the product?

471. Express by equations the actions of (a) chlorine on bromine water, (b) bromine on caustic potash, (c) bromine water on silver bron.ate.

472. What occurs when heat is applied to (a) bromic acid, (b) potassium bromate ?

473. How is perbromic acid obtained? Compare its properties with those of perchloric acid.

COMPOUNDS OF IODINE.

474. Do iodine and hydrogen combine together directly, and if so, how?

475. State fully what occurs when strong sulphuric acid is dropped on potassium iodide.

476. How is hydriodic acid usually prepared? How would you obtain (a) the dry gas, (b) a saturated aqueous solution of it?

477. What occurs when a current of sulphuretted hydrogen is passed through a solution of iodine?

478. What are the properties of hydriodic acid, and what occurs when it is strongly heated?

479. How many cubic centimetres of hydriodic acid at N.T.P. are required to weigh the same as 1,000 of hydrogen?

480. What is the action on hydriodic acid of (a) chlorine, (b) bromine, (c) iodine, (d) sulphur dioxide?