Mr. R. E. Hughes on Water as a Catalyst. 533 



In this instance a decided change undoubtedly takes place, 

 which appears to be totally independent of the absence or 

 presence of water. In one experiment the change observed 

 was 20 per cent, of the theoretical amount, this particular ex- 

 periment being conducted at the temperature of the laboratory. 

 In an experiment conducted at 100° the change was 13 per 

 cent., whereas in another experiment conducted at the ordi- 

 nary temperature, as much as 42*7 per cent, of the theoretical 

 amount of change took place. In all these experiments the 

 gas was allowed to pass for about three hours. 

 . Experiments of a different character were then undertaken. 



An " inactive " solvent, such as anhydrous ether in one 

 case and benzene in another, was taken, and silver nitrate 

 dissolved in it by warming. Through the solution a current 

 of dried HC1 gas was passed. 



For some time no change could be observed, and even 

 after one hour only a very slight turbidity was produced. 



Using absolute alcohol as the solvent, a more decided pre- 

 cipitate was obtained at the end of one hour ; but the change 

 was still only very partial, as was shown by the remarkahle. 

 increase in the precipitate on the addition of a minute 

 quantity of water. 



Mercuric chloride was dissolved in absolute alcohol, and 

 through this solution a current of dried hydrogen sulphide 

 gas (dried according to the method described in Phil. Mag. 

 xxxiii. p. 471) was passed. For about a quarter of an hour 

 or even longer no change was noticed, then a slight turbidity 

 which became more perceptible, very slowly assuming a pale 

 yellow colour, then a darker yellow, and finally a greenish 

 yellow precipitate was obtained. No further change was 

 observed even after one hour and a half — the change is in 

 fact a limited one, and the green insoluble compound pro- 

 duced is doubtless a double chloride and sulphide of mercury. 



The addition of a little water instantly changed this green 

 precipitate to a black one. It is intended to repeat these 

 experiments quantitatively. 



An experiment was conducted to determine whether dried 

 HC1 gas and dried ammonia gas combine when mixed. 



The method was as follows : — Two equally-sized U-shaped 

 glass tubes, with their limbs sealed, and having narrow side 

 delivery-tubes capable of being drawn out and sealed, were 

 taken. One of these tubes, in the bend of which was placed 

 some freshly heated lime, was filled with dried ammonia gas 

 and sealed. The other tube, containing phosphorous pent- 

 oxide in the bend, was rilled with dried hvdroehloric-acid gas, 



