CHEMISTRY. 171 



tents are continually stirred, and when filled a little lime-water 

 is added, and the mixture is allowed to settle during 48 hours. 



The precipitate formed is chiefly composed of sulphate of lead, 

 iodide of silver, and salts of copper, which latter are readily re- 

 moved by washing with water acidulated with chlorhydric acid. 

 The precipitate is then decomposed by metallic zinc, which re- 

 duces completely the iodide of silver, and to a certain extent the 

 sulphate of lead. There result (1) a solution of iodide of zinc, 

 which after being standardized is employed in subsequent opera- 

 tions to precipitate fresh quantities of silver; (2) a precipitate 

 containing about 4.5 per cent, of silver, 0.06 percent, of gold, 

 15.5 per cent, of zinc, and 56.5 per cent, of copper. 



The result of nearly 6 months' experience of this process, at the 

 Widnes Metal Works, shows that one-half ounce of silver and 1 

 grain gold may be extracted from each ton of ore worked at a 

 total cost of Sd. per ton. A profit of 2s. per ton is thus obtained, 

 an amount not to be disregarded in works which treat 30,000 

 tons of ore annually. Abstract of a paper read by J. Arthur 

 Phillips before the British Association, 1870. 



GAS MANUFACTURE. 



Neiv Process of Gas Manufacture. In this process, which is 

 patented, and which is at present in operation under the auspices 

 of the Citizens' Gas Light Company, Saratoga, N. Y., the gas is 

 made from crude naphtha in an essentially " new" method. 



The naphtha is put into a still and gradually converted into 

 vapor by a steam coil. The vapor is thence conducted into a 

 peculiarly constructed superheater, placed inside a clay or iron 

 retort, set and heated in the usual way. There is in use 

 here one bench of 3, each retort provided with a super- 

 heater. The vapor enters the rear of the retorts from the 

 superheater, where it is instantly converted into a fixed gas, 

 and passes into the stand-pipes, and so on to the gas-holder 

 in the usual way, except that no washing, scrubbing, or puri- 

 fication is needed, a simple tank and condensing' coil being all 

 that is required. 



One bench of 3 will produce 5,000 feet of gas per hour, pre- 

 pared for distribution, of not less than 20 candle-power, equal 

 to 120,000 cubic feet per day of 24 hours. One bench of 5 will 

 easily produce 200,000 cubic feet per day. The expense of labor 

 is reduced to a minimum ; only an engineer and one fireman 

 being necessary. The entire process is so nearly automatic that 

 but little manual labor is required. There is no charging and 

 discharging of retorts, no troublesome stoppage of stand-pipes, 

 or scaling and decarbonizing of retorts, no laborious and disagree- 

 able purifying process. There are no bad odors, smoke, or soot. 

 The first cost of works, it will be readily understood, is much less; 

 scrubbers, washers, and purifiers being dispensed with, and only 

 one-tenth the number of benches being required to produce a 

 given amount of gas, and, owing to the low heats employed, the 



