MECHANICAL AND USEFUL ARTS. 89 



across into France, with a power far surpassing that of any other fixed 

 light within sight, or anywhere existent. The experiment has been 

 a good one. There is still the matter of expense and some other 

 circumstances to be considered ; but it is the hope and desire of the 

 Trinity-house, and all interested in the subject, that it should ulti- 

 mately justify its full adoption. 



GAS LEAKAGE AND ITS EFFECTS.* 



An able Report, made by Mr. Spencer, the analytical chemist, and 

 the acknowledged discoverer of electro-type, has a peculiar bearing 

 upon the question of the purification of the Thames, its summer 

 stench, and its black mud. Now this mud, Mr. Spencer maintains, 

 after investigations for several years past, is not only the legitimate 

 offspring of the stinking black earth of the London street subsoil, 

 but also the special source of the summer stench of the river in the 

 metropolitan bounds. 



The origin of this stinking black mud, Mr. Spencer traces, not to 

 the sewage of London, but to the abundant percolations of the black 

 earth of the street subsoil into the sewers, and this black earth he 

 traces back without difficulty to its well-known source in gas leakage. 

 But he does not attribute this abomination merely to impurities in 

 the gas so leaking, but to the gas itself, however pure or impure ; 

 and of this gas the quantity which leaks from London gas-pipes is 

 something enormous, — no less than 9 per cent., or between six and 

 seven million cubic feet per annum. No such leakage occurs in other 

 populous towns, such as Liverpool or Manchester, where the joints of 

 the pipes are bored and turned, and so fitted to each other like glas3 

 bottles to their ground stoppers ; whereas, the London gas-pipes are 

 jointed with tow and lead, so that, after a little endurance of changes 

 of temperature in summer and winter, and consequent expansion 

 and contraction, the lead parts from the more expansive iron in 

 summer, and is compressed by the more contractile iron in winter, 

 in such a way as to destroy the joint entirely as a tight fit, especially 

 for gas. 



The gas so allowed to leak in enormous and perpetual quantities 

 has been found by Mr. Spencer to react upon the gypsum or sulphate 

 of lime in the London subsoil, and thus to liberate the sulphur from 

 its harmless combination with the lime, and promote its union with 

 the carbon of the gas ; forming a vile sulphuretted carbon, which 

 corrodes not only the gas-pipes but the water-mains also, and con- 

 verts them almost entirely into a sort of plumbago in ten years ; 

 although in pure London subsoil they will last for a century. The 

 corroded matter crumbles, and is converted into black, foid earth ; 

 and, according to Mr. Spencer's investigations, percolates, with 

 moisture, into the sewers, chiefly from above, and not only subsides 

 into the heavy black "slike" of the Thames banks, but is actually 

 choking up the sewers themselves. 



* " Report to the New River Company on the Corrosion of Iron Mains, and the 

 effects of Gas Leakage on the Metropolitan Street Earth." By Thomas Spencer, 

 F.C.S., &c. Printed by J. liedderwick and Son, printers to Her Majesty. I860. 



