PURIFIERS. 117 



than sufficient to overcome the pressure of the gas in the purifier when 

 the valve on the inlet-pipe A is closed, which should be done before that 

 at K is opened. 



L is a cylindrical vessel, open at the top, for filling the purifier ; it also serves 



to show the quantity of water required ; when the machine is at work the 



column contained in the vessel will be as much higher than that in the 



tank, by the pressure of gas in the gasometers, usually about three inches. 



The explosion at Peter Street, mentioned at page 18, was occasioned by the 



gas escaping with the lime-water, no sealing-tube being attached. 



The lime-water may be mixed in a cistern (having its bottom above the level 

 of the water in the purifier when filled, and furnished with an agitator worked 

 by hand), and drawn off by a hose into any of the machines, care being taken 

 to keep the mixture well agitated while passing. The proportions are one 

 measure of paste-lime to three of water ; that is, to every five bushels of paste- 

 lime about 120 gallons of water must be added. The size of the lime-machines 

 ought to be so regulated that they will contain sufficient lime-water to purify 

 the quantity of gas made in twenty-four hours, without having occasion to fill 

 them higher than the water-line shown in the engraving. 



Four lime-machines are necessary, two being in action and two out, alter- 

 nately. When that machine is spent through which the gas first passes, shut 

 it off, and open a third, leaving the second to perform the duties of the first, 

 and so on. The following extract from Mr. Clegg's Journal will give his 

 opinion on the construction and use of lime-machines : 



" The grand principle of the construction of a lime-water purifier is to divide the gas 

 as minutely as possible, at the same time avoiding unnecessary pressure. If the machine 

 is well constructed, seven or eight inches pressure in each machine is quite sufficient. 

 Two sets are necessary, in order to have a pair clean and ready for immediate use. The 

 practice of working the contents of the vessel over again, by passing them from one to 

 another, is mistaken oeconomy." 



I have before stated that the quantity of lime required for the complete pu- 

 rification of coal-gas varies very much with the quality of the lime and the 

 gas ; that coal which produces the greatest volume of sulphuretted hydrogen 

 from the presence of iron pyrites will require the most lime. As the best 

 means for arriving at a proper practical conclusion, I annex the quantities 

 used at different gas-works in various parts of the kingdom. 



At the Imperial Gas-Works, London, one bushel of quicklime purifies on 

 an average 10,000 cubic feet of gas, the price of lime being 7d. per bushel. 



