LESSONS IN CHEMISTRY. 





which condense in the pipe* and *eriou*ly affect the passage of 

 the gas. If, on the oth< r l.,u..l, t>.,- .:.,;, ...;..:,. be raised too 

 i.i^h. thru M.IIM- i.i tin; prrnmiifiitly gaseous hydrocarbon* which 

 u ro necessary to the illuminating power of the ga* become 

 decomposed, and their carbon i* do^oxiu-il . :i the inrfaoe of 

 the retort. l-'rm thin the charcoal- point* for the electric light, 

 tho plates for galvanic batterion, etc., are i The de- 



livery tubcH from tho retorts IK-IK! into th. le tnotn, 



utiidi i- :i |.i|,t- of largo diameter half filled with wu 1 

 tubes dip lirnrath tho Miirfuce of the water, which retaini tho 

 n.luMt! i r ..lucts of the diatillation, and those easily condensed, 

 \vhil<> the gas bubbles through the watvr and collects in the 

 upper p;irt of the mtiin. 



lio tar accumulates it flows over into the tar-welli, to 

 v.-hirh it in conducted by the same pipe which loads the gas to 



ndensers, which are a number of upright tubes, bent 

 sharply ut their extremities. They are kept cool by water, 

 which is allowed to trickle over their surface from a cistern 



them. In circulating through these serpentino pipea the 

 gas is ooolod, and the remaining tor and aqueous vapour is con- 

 densed, and the gas alone passes on to the purifiers. The 

 latest and inoat improved method of purifying the gaa is causing 

 it to pass over shelves, on which is a mixture of moistened 

 sawdust and ferric oxide ; .slaked lime was, and is still, fre- 

 quently used. This process deprives the gas of its carbonic 



iilphuretted hydrogen, sulpho-cyanogen, and ammonia. 

 The dirtulphido of carbon which is still nnremovcd may be 

 separated by passing the gas over sawdust sprinkled with a 

 solution of oxide of load in caustic soda ; but this is not usually 

 done, although it is owing to this impurity that plants cannot 

 live in gas-lit rooms. The gas is now ready for consumption, 

 and is stored in gasometers. A ton of good Newcastle coal 

 yields an average of 9,250 cubic feet of gas. 



The products derived from Coal-Tar are numerous. When 

 it is distilled, the first product is ammonia; water then passes 

 over, charged more or less with ammoniacal salts, and on the 

 surface of the distillate an oil begins to accumulate ; in due 

 time the aqueous vapours cease, and nothing but this oil distils. 

 If allowed to be in contact with the air, certain constituents of 

 the oil absorb oxygen, and turn brown. On the addition of a 

 little sulphuric acid, the liquid separates ; the clear supernatant 

 liquid is coal naphtha. A further distillation gives dead oil, 

 which is used to preserve railway-sleepers from rotting, for 

 burning to produce lamp-black, and for fuel in common lamps. 

 The residue in the retort is pitch. 



Benzole, Benzine, or Phene (C a H 8 ). Faraday first procured 

 this substance from oil, made by the compression of oil gas ; 

 but now it is obtained in large quantities from coal naphtha. It 

 is very inflammable, burning with a bright flame. It is a sol- 

 vent for caoutchouc, gutta-percha, and fats ; hence it is used for 

 removing grease-stains from soiled fabrics. When hot it dis- 

 solves sulphur, phosphorus, and iodine. When added to warm, 

 fuming nitric acid, very slowly, one of its atoms of H is replaced 

 by a molecule of NO 2 , thus forming C 8 H 5 ,NO a (Nitro-benzole), 

 a yellow oil, which rises to the surface of the acid mixture when 

 cooled. It possesses the odour of bitter almonds, and is there- 

 fore used in perfumery as essence of mirbane ; but its most 

 important use is tho production of aniline. The mode of pro- 

 cedure is add to the nitro-bonzole a mixture of equal parts of 

 alcohol and hydrochloric acid, then add fragments of zinc ; 

 by this means, the monad XO 2 is replaced by a molecule of 

 amidogen (NH 2 ), thus : 



C.H,, (NO,) + 3H, = C H, (NH,) + 2H,O. 



Hence aniline may be properly called amido-benzole. It is a 

 colourless liquid, but if to its solution in water a solution of an 

 alkaline hypochlorite be added, a splendid red is produced. To 

 produce the mauve dye, cold dilute solutions of aniline sulphate 

 and potossio dichromate are mixed in equal proportions, and 

 allowed to stand twelve hours. The block precipitate is then 

 washed upon a filter, cleaned by digesting with naphtha, and 

 finally taken up by alcohol, upon the evaporation of which tho 

 dye in a pure state is procured. It is freely dissolved in hot 

 water. Certain mordants are required by certain materials. 



Rosanilinc or Magenta. This body is formed by the effect 

 of feeble oxidising agents on aniline. The plan usually adopted 

 is to mix 20 parts of syrupy arsenic acid with 12 of commercial 

 aniline. The mixture is heated in a retort to about 170 Cent. 



Water and some aniline di*til over ; the residue, which i* of a 

 bronse colour, is poured oat on an iron plate, broken into frag- 

 ment* when cool, and digested in twio* its weight of hydro- 

 chloric add in tank* heated by steam. The r*d liquid thus 

 obtained is .trained off. and whw treated with sodio carbonate, 

 flakes of rosaniline are precipitated. 



VEOETABLB COLOUBIHO MATTERS. 

 The colouring matter in plants doss not reside in any par. 

 ticular part of their structure the roots, the wood, or the flower 

 may contain it. The simple colouring natter so extracted i* not 

 very stable, being acted upon by the oxygen of the air and the 

 sunlight. But innoluble compound* are formed with earth and 

 some metallic oxides, snob as thoee of lead or tin. These com- 

 pounds are termed lakes, and it i* the art of the dyer and 

 calico-printer to saturate the fabric with the mordant, and than, 

 when immersed in tho dye, a lake is formed in the fibre of the 

 cloth, which is thus dyed /cut. We shall enumerate some ot 

 the most prominent dyes. 



YELLOW DTES. 



Saffron is yielded by the flowers of the Crocus tativta. 

 Turmeric, or curcumin, i* used for colouring the curry-powder 

 of India, as well a* for dyeing. With alkalies it turn* brown ; 

 hence it i* used in the laboratory a* a test for those bodies. 

 Common rhufxirb yield* a colouring matter termed rheint or 

 chrysophanic acid. 



The Clusiaceae, or the gamboge family, yield a yellow pig- 

 ment much valued. The shrubs are natives of Siarn. 



BCD DYES. 



Madder Is extensively used for dyeing reds and purples. It 

 is procured from the root of the Rulia tinctontm, which growc 

 in the Levant and in the south of France. 



Logwood, so much used a* a red, and with alum a* a black dye, 

 i* the wood of the tree Haematoxylon (&<M, blood ; (i/Aor, wood), 

 a native of the West Indies. Under the influence of sftaKss 

 and oxygen a bright red is procured. The colouring principle 

 which the wood contains i* called haematoxyline. 



Brazil-wood is not unlike logwood. It yield* bretiline, which, 

 with alumina is the basis of red ink. The pink saucers of the- 

 artists are from tho " safHower," and the same colour imparts a 

 brilliant rose-red to silks, but it i* much injured by sunlight. 



Carmine is contained in cochineal. The insect was originally 

 a native of Mexico, and feeds upon the cactus. The instxwi- 

 are collected from the plants with a blunt knife ; they are then 

 steeped in hot water, and dried in the sun and exported. The 

 colournmn boils them in water in large vats, the cochineal being 

 suspended in bags. The colour pf the powder is affected by the 

 temperature of the water. With oxide of tin it is used for 

 dyeing cloth crimson. Lao dye and extract of aloes are two 

 substances of the same class. 



BLUB DYES. 



Indigo contains a colouring principle termed \ndiyotint, from 

 which several derivations have been prepared. It is extracted 

 from the leaves of the indiyofera, a plant growing in India and 

 America. In the early summer, the plants, just before flowering, 

 are cut, and placed in troughs. Slightly pressed, they are 

 covered with water, and a species of fermentation goes on, and 

 carbonic acid and ammonia are disengaged. If the fei mentation 

 bo allowed to proceed too far, the indigo decomposes. Booh is 

 also the case if boiling water be used in its separation. When 

 the liquid appears like sherry wine, it i* drawn off, agitated^ 

 with oars, upon which the dark-blue powder fall*. Thin preci- 

 pitate is then washed, pressed, and dried. With Nordhausen 

 sulphuric acid indigo forms a compound which U exteasmsr ' 

 used in dyeing cloth, under the name of Saxony blue. 



The Lichens afford several well-known dyes, snob as cuatssr, 

 archil, litmus. The last, so well known in the laboratory, if 

 derived from a lichen, which growc on rocks on the coasts of 

 the Canary Islands, the Cape of Good Hope, the west coast of 

 South America, and other localities. 



The colouring matter which is so widely diffnsnd in Nature 

 giving the landscape a uniform tint of green, is of a reaiaou* 

 nature, which can be dissolved by alcohol and ether It ha* 

 been named chlorophyl. The change of the colour of the fnKags 

 during the progress of the seasons is doe to the alteration* of 

 the colour of the chlorophyl. 



