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338. Describe the various kinds of naturally occurring water. Arrange them in order from the purest to the

least pure.

339. Why is river-water more impure than rain-water? What does the latter contain ?

340. Of what is pure water composed ? Who discovered the composition of water ? How and when was the discovery made?

341. Sketch the apparatus you would use to show the decomposition of water by the galvanic current.

342. Give all the ways you know for obtaining (a) hydrogen and (6) oxygen from water.

343. Cavendish exploded a mixture of 19,500 measures of oxygen with 37,000 of hydrogen. Which gas would remain after the explosion, and how much of it?

344. How could you show that water is produced by burning hydrogen in air or oxygen? Water is also produced when a candle or a gas-jet burns in air. How do you explain this ?

345. What weight of hydrogen and of oxygen is contained in 100 lbs. of water ?

346. A gas-holder contains 71 litres of hydrogen at N.T.P., what volume of oxygen is required for its combustion, and what weight of water would result ?

347. A strong glass flask containing 200 c.c. hydrogen and 100 c.c. oxygen weighs 417 grammes. An electric spark is passed through the mixed gases. What is the weight of the flask when cold ?

348. How is the composition of water ascertained by means of the eudiometer ? Give the details of the


349. After exploding a mixture of hydrogen and oxygen, o‘017 gramme water was obtained, and 11'5 cc. hydrogen remained. The temperature was 15o C. and the pressure 760 m.m. Find the volume of the mixed gases.

350. What volume of steam is obtained by exploding a mixture of two volumes of hydrogen with one of oxygen ?

351. Sketch Hofmann's apparatus for showing the volume of steam obtained by the explosion of a mixture of hydrogen (2 volumes) with oxygen (i volume), and explain how it is used.

352. What happens when hydrogen is passed over heated copper oxide ? Express the reaction by an equation.

353. Explain how the action of hydrogen on copper oxide may be used as a means of determining the composition of water.

354. Berzelius and Dulong heated 53-821 grammes copper oxide in contact with hydrogen. The residual copper weighed 42.989 grammes, and 12.197 grammes water were obtained. Calculate from these data the percentage composition of water.

355. Sketch Dumas' apparatus for the determination of the composition of water, and state the precautions he took to ensure the purity of the hydrogen employed.

356. As the result of numerous experiments Dumas found that 840°161 grammes of oxygen were required in the production of 945-439 grammes of water. Calculate from these data the percentage composition of water and the combining weight of oxygen.

357. One gramme of hydrogen is passed over 172 grammes of red-hot copper oxide. Find the weight of water produced, and the loss of weight of the copper oxide.

358. 53'5 c.c. of water were obtained by the action of hydrogen on heated copper oxide. Find the volume of hydrogen used, and of the oxygen with which it combined (both gases measured at N.T.P.).

359. What weight of iron sesquioxide, if heated in hydrogen, would be required to yield 12-7 grammes water, and what volume of hydrogen at N.T.P. would be used in the reaction ?

360. Twenty litres of hydrogen measured at 15o C. and 754 m.m. are burned in air, and all the water produced is collected. Find the weight of the water and the volume of air required.

361. Give six equations to show that water is a frequent product of chemical reactions.

362. Explain each of the following terms—(a) water of crystallization, (6) hydrates, (c) deliquescent, (d) hygroscopic, (e) efflorescence, and (f) cryohydrates. Illustrate the meaning in each case by examples.

363. At what temperature is the density of water greatest? How may this be shown experimentally ?

364. Starting with water at 15° C., explain the physical changes which occur (a) when it is heated to 100° C., (6) when it is cooled to o° C.

365. How does the pressure of the atmosphere affect the temperature at which water boils ?

366. What is the crystalline form of ice and snow? How may it be observed in each case ?

367. What use is made of water in graduating a thermometer? Why is it chosen for this purpose ?

368. At what temperatures does water boil and freeze respectively on the three thermometric scales in common use ?

369. How may degrees on one scale be calculated into degrees on the others? What temperatures on the centigrade and Reaumur scales correspond to 15° Fahrenheit?

370. Sulphur melts at 115o C. and boils at 440° C. and sulphur dioxide boils at 8° C. Calculate these temperatures on the two other scales.

371. What changes in bulk occur (a) when ice melts, (6) when water freezes, and (c) when water is heated ?

372. Two thin glass tubes are filled with water and sealed up ; one is placed in boiling water, the other in a freezing mixture. What occurs in each case ?

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