LKSSONS IN CHKMISTKY. 



The following shows the clear gain made by the purchase and 

 salo of C'otton from January tx> Jane, an per Cotton-Book : 





LESSONS IN CHEMISTRY. XI. 



CARBON AND ITS OXIDES. 

 CABBON. SYMBOL, C; ATOMIC WEIGHT, 1:2. 



No solid plays a more prominent part in the economy of nature 

 tliiui ciirlion, as it forms well nigh the whole of the wood of vege- 

 ta t ion . It is a very romarkable substance, for it appears in three 

 perfectly distinct states the diamond, graphite, and charcoal. 



1. The diamond in found in alluvial debris that is, in 

 water-worn deposits of gravel. It is presumed that the gem 

 was formed by crystallisation when the rock was in a fluid 

 state, and when in after ages it became broken in pieces by the I 

 action of water and other geological forces, the hard diamond , 

 was delivered from its matrix, and mixed with the debris. The 

 chief diamond mines are those of Qolconda and Bundelcund, 

 in India, Borneo, and Brazil. 



When found, the stone has the appearance of a piece of 

 white glass ; occasionally there is an approach to the crystal 

 form of the octahedron. 



It is the hardest of all known bodies, and is capable of , 

 dispersing light that is, of breaking up white light into its } 

 coloured component rays in a greater degree than any other 

 body except chromate of lead. To exhibit this property to its 

 full advantage, the gem must be out. This was once an opera- 

 tion of the greatest difficulty, and could only be executed by 

 tho Dutch diamond-cutters, who fastened two stones in cement, 

 and then rubbed them against each other until a facet was pro- 

 duced. Now, diamond-cutting is much less laborious. The 

 stone is fixed, as before, in a metallic cement, and pressed upon 

 a disc of steel about eight inches in diameter, which revolves 

 horizontally with a great velocity. As with all crystals, there 

 are certain directions in which tho diamond is more readily cut. 

 It is the skill of the cutter to place the stone upon the disc in 

 the right position. The steel, were this not done, would itself 

 be cut, instead of making any impression on the diamond. 

 The secret of the disc being enabled to wear down the hard 

 mineral is, that the minute interstices of the metal become filled 

 with dust from the diamond. This is in many instances applied 

 to the plate mixed with olive oil ; but when a disc has been 

 some time in work, it is sufficiently impregnated with the dust 

 not to need this addition. 



In the Brazil mines is found a dark brown carbonaceous 

 matter, in small pieces, which is as hard, if not harder, than 

 the diamond itself; and it commands as high a price on account 

 of its use in forwarding the cutting of the stones. 



The most important use of the diamond is the cutting of glass. 

 This is effected by a natural face of the crystal. If the edge be 

 formed by the intersection of two artificial faces, the cut produced 

 on the glass is not a true cut, but only a scratch with rugged 

 edges. The natural faces of the diamond are frequently curved. 

 Tho diamond may be heated intensely in an atmosphere of any 

 gas except oxygen, but if it be suspended in a cage of platinum 

 wire, and heated to a bright redness, and then plunged in a jar 

 of that gas, it burns with a steady red light, producing carbonic 

 *cid gas (C0 2 ). 



It was reserved for Sir H. Davy to show that this gas was 

 tho sole product of the combustion of the diamond, though tho 

 fact that it was combustible was known in 1694 to the philo- 

 sophers at Florence. The combustion, however, is not complete, 

 as there always remains an ash, which is generally in the form 

 of a cellular network the skeleton, as it were, of the gem, and 

 which consists of silica and the oxide of iron. With this excep- 

 tion the diamond is pure carbon. When submitted to the most 

 intense of heats, that of the voltaic arch, the diamond loses its 

 transparency, begins to swell, and is converted into a black 

 mass resembling coke, the amorphous form of carbon In this 

 state it is a good conductor of electricity, a property it does not 

 possess in its transparent condition. 



2. Graphite or Plumbayo, erroneously oalled btaeUtai, is all 

 but pure carbon, slight traces of iron generally bain* present. 

 It is a crystallised body, belonging to the thud or Bhomhohe. 

 dral system. The distinction between this and the first or 

 regular system, in which the diamond mjstsllisss, wfll be 

 explained in a future lesson OB erysteJHeatioB, It ocean in 

 veins, always in rooks of the earliest formations. The most 

 celebrated mine is that of Borrowdale, in Cumberland. Here 

 it is found in "nests " in trap traversing clay slates. It is a 

 good conductor of electricity, and is as difficult to born as the 

 diamond. It is chiefly used for ****pnf* r 't T w^*'g lead 



Being very friable, it leaves its particles on paper when pssssd 

 across it The particles themselves, however, are extremely 

 hard, and soon wear out the saws with which the graphite 

 is out. 



Formerly good pencils could only be made from lamps suffi- 

 ciently large to permit of long pieces being cat. The small 

 mssBOS and dust were cemented together with sulphur, but by 

 this the " marking " quality of tho graphite was so injured that 

 only the coarsest pencils could be made of it. But it has been 

 discovered that by submitting this dust to enormous pi emote 

 it will cohere, forming plates fit for the manufacture of the 

 best pencils. 



Graphite is used for lubricating machinery, and also for 

 making crucibles. For this purpose it is mixed with fire-clay 

 These crucibles are not so liable to crack as those made of clay 

 only. 



3. The third form of carbon has no appearance of niyntsflisa 

 tion. It is therefore said to be "amorphous," or without form. 

 This state is shown in coal, charcoal, soot, etc. Of the composition 

 of coal we shall treat in the next lesson. Charcoal is got 

 from the " destructive distillation " of wood that is, the wood 

 is heated in vessels of iron, closed so that no air can cause the 

 carbon in the wood to burn. Of course there is a pipe to carry 

 off the gases liberated by tho heat. If blood or bones be sub- 

 mitted to this process, the result is animal charcoal. 



Wood charcoal is also made by cutting the wood into logs, 

 and arranging them on end, then covering the whole with sods, 

 and setting fire to the heap at some central point. A portion 

 of the wood is consumed, but the heat thus produced convert* 

 the remainder into charcoal. Charcoal is a bad conductor of 

 heat and electricity. It is very porous, in virtue of which. 

 like spongy platinum, it absorbs gases, the quantity varying 

 with the nature of the gas. Thus, boxwood charcoal absorbs of 



Volume*. 

 85-00 



Hydrochloric acid gas 

 Sulphuretted hydrogen 



Carbonic add gas 

 Oxygen 



35-00 

 925. 



When heated or placed in vacuo, these gases are again given 

 off. Whilst in this state of condensation their powers of 

 affinity are greatly increased. Thus sulphuretted hydrogen at 

 common temperature is not altered by contact with oxygen ; 

 but if a piece of charcoal which has absorbed the former gas be 

 plunged into a jar of the Utter, a detonation ensues from 

 the violence of the combustion, water and sulphuric acid being 

 formed : 



SH, + 30 = H,O + SO,. 



This power is also shown in what are termed the 

 properties of charcoal that is, the power it has of removing 

 offensive smells. If putrefying meat or fish be packed in char- 

 coal, all smell is removed; for the gases which cause the 

 unpleasant effluvia are absorbed by the charcoal ; and whik 

 in this state the oxygen, previously in its pores, attacks and 

 changes the various gases, or oxidises the volatile organic 

 matter. The process of putrefaction, however, is not arrested, 

 but rather increased. This is often resorted to by unprincipled 

 butchers and fishmongers who present tainted meat or fish for 

 sale, which escapes detection for the moment by its inodoroos- 

 neas. Yet it possesses all the deleterious properties of unwhole- 

 some food. Charcoal, especially animal charcoal, clears coloured 

 liquids which are passed through it This may be well illus- 

 trated by shaking a little of it with a few ounces of port wine 

 in a bottle, and then filtering the mixture ; the liquid which 

 passes the filter will be colourless. 



Sugar is clarified by means of charred bullock's blood. After 

 being in use for some time the charcoal is found to lose its 



