Clifton College ScienUjic Socieiy 111 



acetylene (CoPL) is present in small quantities. If the ordinaiy gas 

 we are in the habit of burning is passed through cupreous oxide, the 

 characteristic red precipitate (CjH Cu2)20 is formed, and indeed in 

 this way it may be prejjared pure by the addition of H CI. 



Hydrogen is rather detrimental than otherwise to the luminosity, 

 but for heating purposes of great use. In 100 vohimes of coal gas 

 between 34 and 13 are H. CO is 2)resent, but it is not easily separated 

 from the other gases, and, as there is only about 7 per cent, of it, it is of 

 no great harm, though poisonous if present in miicli larger proportions. 



The gas is usually contaminated with N and O, the presence of 

 which may be accounted for by knowing that the pipe joints are not 

 perfectly tight, and therefore ch'ffusion takes place. 



The luminosity of the gas is in some degree, as well as its smell, 

 due to the vapours of volatile hydro-carbons. In a very hard frost 

 gas seems to loose some of its lighting jjowers ; the fact is that these 

 hydro-carbons are condensed in the pipes, but again volatilize on the 

 temperatui'e rising. There are generally traces of caibon di-suli)hide, 

 the most noxious of its constituents, but the quantity is very small 

 indeed. If, however, gas be drawn through a tul)e iu which a red hot 

 coil of copper is placed, after several hours it will be found to have 

 been coated with a black deposit, which is copper sulphide. The 

 cracking of the bindings of books, and tarnishing ot the gilding on 

 pictures is due to this, and the reason silver becomes discoloured so 

 quickly in the great towns is from the presence of CS2 and SOo. These 

 ore the most important constitnents of the gas we burn, and I will 

 now pass on to the bodies previously separated in the condensers and 

 purifiers. 



Tar and volatile oils form a large portion of the product of the 

 destructive distiHatiou of coal ; these bodies for the most part having 

 a high boiling point, condense in the hydraulic main, together with 

 water containing the NH- in solution, the moi'e volatile compounds 

 being condensed in the refrigerators. The liquid is treated with 

 weak hydro-chloric acid, by which the alkali is neutralised, and the 

 liquid is separated by mechanical means, as far as possible, from the 

 tar. 



The solution containing ammonium chloride, and impurities is 

 evaporated to dryness in iron cauldrons, and carefully heated to expel 

 or decompose the tarry matter, it is then purified by sublimation, in 

 large iron vessels lined mth clay, and surmounted by domes of lead. 

 The crystals thus obtained have a fibrous texture, and are tough and 

 consequently difficult to powder. This salt occurs native in many 

 volcanic districts, also in small quantities in sea water ; but our supply, 

 before it was obtained from ammouiacal liquor, was from Egypt, where 

 it is prepared by sublimation from the soot of camels' dung." 



This salt is of great use in the laboratory, for from it NH3 is easily 

 prepared, also for freezing mixtures. It is employed in dyeing, and in 

 metal works as a deoxidising agent, especially for copper. It enters 

 into the composition of a cement used for fixing iron into stone : this 

 is formed by moistening, with a solution of sal ammoniac, iron filings 



