120 PEOCEEDINGS OP THE AMERICAN ACADEMY 



now poured 40 litres of hot water, heated to between 70° and 80° C, 

 and then 5 litres of common oil of vitriol are poured very cautiously 

 into the same bung through a lead funnel with narrow spout provided 

 for the purpose. The acid water will thus be heated nearly to the 

 boiling point, and its capacity of dissolving ferrous sulphate raised to 

 the maximum. Next 6 kilogrammes of sulphide of iron — previously 

 sufficiently pulverized to pass through a wire sieve with eight meshes 

 to the inch, and mixed with two kilogrammes of marble powder — is 

 run through a wide-mouth funnel into the bung B. The bungs having 

 been now all closed, the joints of the apparatus tested, the exit valve 

 D of the generator and all the valves of the fountains opened, a small 

 amount of the powder is sifted down into the acid water by turning 

 the handle not more than a single revolution, always taking care to 

 leave it so that the slits of the diaphragm shall be left covered. The 

 gas is then allowed to stream through the apparatus, and tested as it 

 escapes into the flue, until it burns without explosion, using a small 

 pneumatic trough for that purpose. The air is now nearly expelled, 

 and the escape of gas should be reduced by the last vent valve until 

 the current only su^jplies a small jet, which may now be attached and 

 lighted with safety, and by the size of this flame the vent may after- 

 wards be regulated. The handles are now slowly turned, and the 

 pressure in the apparatus carried up to about 120 pounds. The valves 

 of the fountains and the valve D of the generator are now all closed, 

 and the two last fountains detached, leaving the first (which is mounted 

 on a frame as represented in Fig. 1) united to the generator as before. 

 This is now rocked for several minutes to and fro, in order to 

 thoroughly agitate the water with the gas. The stop valve G should 

 then be opened, and then the valve D (very gradually), so that the gas 

 may be admitted slowly to the fountain. The valves are then again 

 closed, and the agitation renewed, and the same operation is repeated 

 several times until no more gas is absorbed by the water in the foun- 

 tain, the pressure in the generator meanwhile being maintained at 120 

 lbs., by turning the handle. The first fountain is then removed, and 

 the same process repeated with each of the others. At the close of 

 the operation, after all chemical action has ceased, there remains in the 

 generator — both free and dissolved in the liquid residue — a large 

 volume of hydric sulphide gas. This we economize by venting the 

 generator slowly through Woolfs bottles containing aqua ammonia, 

 and thus preparing at tlie same time ammonic sulphide. It is not 

 unimportant to aild that the generator should be emptied before it 

 cools, and the ferrous sulphate has time to crystallize. The discharge 

 valve R should then be removed, and the whole apparatus thoroughly 



