LKSSONS IN 



-71 



1. 2d. 5. la. 5d. 9. 2B. 7}d. 



2. 3jd. 6. IB. I'd. 10. SB. 



3. 7. 1.-. 11. 7B. 3d. 



4. UJU. 8. 2B. 6d. 12. SB. 7Jd. 



Beduoo to tho decimal of a pound oorrootly to 3 decimal 

 place*, by tho method of Art. 10 : 



14. 

 15. 



5Jd. 

 6d. 



16. 

 17. 

 18. 



-s. :;,,!. 

 17s. U{d. 

 18B. id. 



19. 



3 15s. 8Jd. 

 15 19s. ll'd. 



KEY TO EXERCISE 49, LESSON XXX. 



1. '2375. 



2. : 



3. K 



4. -5110 shilling. 



5. jr.iij:. mile. 



6. -127083 day. 



7. -046875 owt. 



8. -2583 hour. 



9. '46875 Ib. 



10. 7, -1 190476, 

 0925. 



11. -5625 acre. 



12. -898809523 guinea 



13. -002739726 of a 



year, '2. 

 i 14. -0089285714, -2. 



15. -03266258384 . . . 



16. -216. 



17. 14a. 6d. 



18. 2s. 7}d. 



. 19. 9d., 3-6 farthings. 

 20. Gor.ir.jVdrachms. 



(Vol. II., page 234). 



21. 88 rods. 



22. 10 h. 13m. 9 A MO. 



23. 50 miu. 42 BOC. 



24. 23 125. 



25. Cs. 8d. 



26. -4114285714. 



27. 178. 9jd., '0006. 



28. -0042 .... 



29. 5s. 4jd. ,V tux. 



30. 196 cubic feet, 



19GJJ cub. in. 



LESSONS IN CHEMISTRY. IX. 



NITROGEN, AIB, ETC. 

 NrrBOGEN : SYMBOL, N ATOMIC WEIGHT, 14 DENSITT, 14. 



NITROGEN is the chief constituent of the atmosphere, of which 

 it forms four-fifths. From being an element of nitric acid, 

 Chatal gave the gas the name here adopted, following tho 

 example of Lavoisier. Tho French chemists call it azote, from 

 its inability to support life. It exists in almost all animal 

 and in many vegetable products. 



To prepare Nitrogen. The simplest method is to deprive air 

 of its oxygen. This may bo done in several ways 



1. Pass air through a porcelain tube containing copper- 

 turning?, which is surrounded by red-hot charcoal. The heated 

 copper combines with the oxygen, and the nitrogen is received 

 in a gas-holder. 



2. In a capsule of Berlin ware (Fig. 31) float a piece of phos- 

 phorus on water ; and, after having ignited it, place over it a 

 bell-jar. The phosphorus takes all the oxygen to form phos- 

 phoric acid (P S O 5 ), a solid, which is readily absorbed by the 

 water, the gas remaining in the jar being nitrogen. 



3. The oxygen may be absorbed from the air slowly, either 

 by suspending in tho jar a stick of phosphorus in this case 

 phosphorous acid (P S O 3 ) is gradually formed or by placing in 

 a capsule a mixture of iron-filings and sulphur moistened with 

 water. The experiment is arranged as the last, but must be 

 untouched for at least twenty-four hours ; by that time all the 

 oxygen in the jar will have been absorbed by the mixture, and 

 the water, rising to fill the place of the absorbed gas, will bo 

 found to occupy one-fifth of the jar. 



There aro other ways of obtaining nitrogen from its com- 

 pounds, thus : if chlorine gas be passed into water impregnated 

 with ammonia, tho reaction will be 



4NH, (ammonia; + Cl, = 3NH.C1 (sal-ammoniac) + N. 



Care must, however, be taken that the ammonia be in excess, 

 lest one of tho most explosive of bodies the chloride of nitrogen 

 be formed. 



Properties. The gas is colourless, inodorous, and tasteless. 

 It is a littlo lighter than air, its specific gravity being 0'9713 ; 

 its affinities are very low ; it refuses to combine with other ele- 

 ments, except under peculiar circumstances. Hence it will not 

 support combustion, and is fatal if breathed in a pure state ; 

 not that it has any poisonous qualities, but is incapable of sup- 

 porting life. 



THE ATMOSPHERE. 



Around our globe rolls a gaseous ocean, which is a mixture of 

 certain gases. Oxygen and nitrogen greatly preponderate over 

 the others, and are found in the proportion of 4 volumes of 

 nitrogen to 1 of oxygen. The chief use of the nitrogen seems 

 to be to dilute the oxygen. That the atmosphere is not a 

 chemical compound, but a mixture, may be thus proved : 



1. If 4 volumes of nitrogen and 1 of oxygen be mixed, no 



alteration, either in volume or temperature, will be observed, 

 and air will bo formed. In every case, when chemical combina- 

 tion takes place, there is invariably either an alteration in 

 volume or temperature, or both. 



2. If air from water, or from melted snow, be analysed, it 

 will bo found that oxygen is present in almost doable the pro- 

 portion in which it is found in the atmosphere. This fact 

 has been already alluded to, as caused by water being capable 

 of absorbing more oxygen than nitrogen. If, however, the 

 gases were chemically combined, tho water must absorb them as 

 one body air, and they would appear in the water in the 

 proportion as in the atmosphere. 



Tho volumes of tho gases in the air may be roughly 

 taincd by abstracting the oxygen from the air in a graduated 

 bell-jar, by burning phosphorus as above described, being care- 

 ful that tho diminution of the volume be measured when the 

 temperature has fallen to what it was at the commencement of 

 the experiment. But the most accurate method is by the 

 eudiometer (Fig. 32). The instrument is used thus : 



The tube is filled with water, then a portion is poured oat. 

 Place the thumb on tho open end, and by properly inclining the 

 tube, tho air may bo made to pass to the scaled end. The water 

 is now made level, so that the air may bo under no undue pressure, 

 and the number of measures of it read off on the graduated 

 scale. The open end is completely filled with water, and the 

 instrument is inserted in a pneumatic trough, where hydrogen is 

 passed into it, the quantity being at least more than half the air 

 in the eudiometer. The instrument is again closed with the 

 thumb, and the mixture of air and hydrogen transferred into the 

 sealed end. The water in the two tubes is again levelled, and 

 the volume of the mixture read off. The instrument is held 

 firmly, as in the diagram, and the platinum wires, a and b, con- 

 nected with the outside and inside coatings of a charged Leyden 

 jar. The spark which passes in the tube fires the mixture, and the 

 oxygen in the air and the hydrogen combine to form water. The 

 temperature is allowed to equalise itself, and the water is again 

 levelled and another reading made. It will bo evident that the 

 difference between tho two hist readings will give the quantity of 

 gas which has gone to form the water in the explosion. Now 

 we know that this consisted of all the oxygen in the air, and 

 some of the hydrogen we introduced ; but we also know that one- 

 third of tho quantity must bo oxygen, this being the proportion by 

 volume of tho gas in water. Hence we arrive at tho quantity of 

 the oxygen in the air with the greatest accuracy. 



To determine the composition of the air by weight, it ir 

 necessary to weigh the copper, in the first process given for the 

 preparation of nitrogen, before and after the experiment, being 

 careful to ascertain the quantity of air passed through the 

 heated porcelain tube. 



Thus the composition of air is 



By volume. 



Oxygen .... 20'93 

 Nitrogen .... 79-07 



By wrght. 

 . 23141 



100-000 



Next to these two gases, the most important ingredients in the 

 atmosphere are vapour of water and carbonic acid gas. To deter- 

 mine their respective quantities, a system of U tubes (Fig. 33) is 

 connected with an " aspirator," which is simply a vessel which 

 has an opening at tho top, and another at the bottom ; it is 

 filled with water, and when the lower tap is turned, it is evident 

 that as tho water flows out air is drawn in through the opening 

 at the top, and by connecting it with the tube?, a current of air 

 is made to pass through them. 



The first two, a and b, are packed with pieces of pumice 

 stone, soaked with sulphuric acid. This retains all the moisture 

 the air which passes through contains. 



It next traverses a system of bulbs, suggested by Liebig, 

 which are partially filled with a strong solution of caustic 

 potash. Here all the carbonic acid gas is absorbed, forming, with 

 the potash, potassium carbonate. The air, however, in passing 

 through the liquid, will take up some moisture, and thus destroy 

 the accuracy of tho experiment; therefore, this moisture is 

 again absorbed by the sulphuric acid in the tube d. A fourth 

 tube, e, similar to d. intercepts any moisture which may attempt 

 to penetrate the tubes from the aspirator S. The tubes a, b, d, 

 and the bulbs c are accurately weighed. The lower tap ia 

 slightly opened, and the air slowly drawn through the tube. 



