28 Mr. H. A. Smith on the Chemistry of 



are brought together in a large globe, and steam is then intro- 

 duced. Ruddy fumes are first formed ; then a crystalline deposit 

 takes place ; and soon the atmosphere in the globe becomes 

 white in colour. But on close examination another peculiarity is 

 seen in the vessel; and that is, that near to the deposit, and long 

 after the ruddiness has apparently disappeared, a very small 

 narrow band of red fumes is noticed wherever the crystallization 

 has taken place. This, then, led to the question being asked, 

 Does not a greater formation of acid take place when some acid 

 previously formed is present ? and this question was attempted 

 to be answered by the following experiments. 



Exp. X. A layer of sulphuric acid from which all moisture 

 had been expelled by long boiling, and which had been pre- 

 viously carefully weighed, was laid in the bottom of the vessel, 

 and the gases allowed to enter, steam being excluded. The gas 

 at the upper part of the vessel became almost immediately 

 nearly white ; but a strong and long-continued action seemed to 

 be taking place at the bottom, near the surface of the sulphuric 

 acid, no apparent action being noticed towards the top. On 

 examination no sulphurous acid was found, whilst the weight of 

 acid originally present had greatly increased. (In this experiment, 

 as in the former, the vessel was allowed to stand twenty-four 

 hours.) This seemed to answer the question, especially as on 

 many repetitions the same results were obtained. 



I felt these perfectly satisfactory as laboratory experiments. 

 Some had now to be attempted on a large scale ; and through 

 the kindness of an acid-manufacturer I was enabled to make 

 the desired trials ; but as in every case I sustained signal defeat, 

 being neither able to cool the chamber sufficiently nor raise it 

 to the required temperature, I found I must, after many dis- 

 appointments, rest satisfied (as many have found themselves 

 obliged to do) with a knowledge of the fact that what appears 

 perfect in the laboratory will not bear the crucial test of manu- 

 facture ! 



I still felt satisfied that I had proved the drawback to this to 

 be want of control over the unwieldiness of the chamber. But 

 one fact came out very strongly — that if I wished a good yield of 

 acid, the increase of steam must be in proportion to the increase of 

 temperature. 



The point which next claimed my attention on the manufac- 

 turing scale was the question, In what part of the chamber 

 does the greatest formation of acid take place ? 



This investigation resolves itself into two separate ones ; — 



1 . The distribution of gases in the lead chamber. 



2. The distribution of heat in the lead chamber. 



The answer to the first of these embodies almost necessarily 



