ON THE ATOMIC WEIGHT OF CHLORINE. 179 



that the absorption of chlorine had not been complete, but, at the end of our 

 experiments, its lustre was unimpaired. 



Preparation of Silver Chloride. Commercial silver nitrate was purified by re-crys- 

 tallisation twice from water. A strong solution of hydrochloric acid was prepared by 

 cautiously distilling the pure concentrated acid, washing the evolved gas with a little 

 water and then dissolving it in re-distilled water, kept cool by means of an ice and 

 salt freezing mixture. 



A strong solution of re-crystallised sodium chloride was prepared, and into it was 

 passed the acid gas evolved by heating the solution of hydrochloric acid previously 

 made. The precipitated sodium chloride was washed with a little ice-cold water, 

 dissolved in fresh re-distilled water and again re-precipitated by means of hydrochloric 

 acid gas. This re-precipitation was carried out three times. Silver chloride was 

 then prepared by adding a dilute solution of the re-crystallised silver nitrate to excess 

 of a dilute solution of the purified sodium chloride. 



The precipitation of the silver" chloride and all subsequent operations were carried 

 out in the absence (as far as possible) of actinic light. The supernatant liquors were 

 decanted as soon as possible and the silver chloride washed repeatedly with boiling 

 distilled water, until a test portion of the washings gave no cloudiness with silver 

 nitrate. The silver chloride was then frequently agitated with more hot distilled 

 water and allowed to stand in contact with it for some time. Then the final washings 

 were decanted and the silver chloride was dried as completely as possible in large 

 porcelain dishes on a water-bath. It was then cautiously fused in deep porcelain 

 crucibles and kept in the molten state for twenty-four hours, care being taken to 

 prevent contact, during the prolonged heating, between the acid gases of the flame 

 and the molten chloride. The chloride was then poured into a clean silver trough so 

 as to form thin sheets. These, on cooling, were easily detachable, and were cut into 

 small fragments. The silver chloride prepared in this way was a colourless, horn-like, 

 translucent substance, which could be easily broken or cut into small pieces. 



The operation of fusing the requisite amount of silver chloride in the U-tube A 

 was carried out as follows: The U-tube (filled through the side tube F with the 

 solid pieces of silver chloride up to the level of the carbon electrodes) was gradually 

 raised in temperature by heating the cast-iron box in which it was closely packed 

 round with asbestos. A high-range thermometer, with its bulb resting on the bend 

 of the U-tube, indicated the temperature of the chloride. When the contained silver 

 chloride had fused, more was slowly added until the calculated amount, 800 grammes, 

 had been completely reduced to the molten state. The side tube F was then sealed 

 and the whole apparatus was exhausted by the pump. When the tubes were 

 thoroughly evacuated the tap P was closed, and the current from one storage cell 

 was passed through the silver chloride for a short time. The current was then 

 increased by the addition of another cell, and chlorine was steadily evolved until the 

 whole of the apparatus on the left-hand side of the tap was filled with chlorine at a 



2 A 2 



