128 On the Chemistry of Sulphuric Acid-manufacture. 



In Diagram III. we find a higher average of temperature, vary- 

 ing for the most part between 150° and 166° F. ; whilst at en- 

 trance and exit the temperature is comparatively low, rising 

 towards the centre of the chamber. Here, now, we approach 

 very nearly the required temperature, 200° P. being the observed 

 degree at which nitric acid acted on sulphurous acid; and by 

 reference to my former paper we find that this portion of the 

 chamber is really the "working" portion. It is necessary also 

 to observe along with this diagram the next, Diagram IV. In 

 my former paper I showed experimentally, by analyses of the 

 gases at 3 feet from bottom of chamber, that the greatest amount 

 of action went on at that portion; and I have shown also (Sec- 

 tion III.) that the temperature at which nitric acid began to 

 act on sulphurous acid was 200° F.; so that now by observing 

 these two diagrams we see how closely the laboratory and the 

 manufacturing results agree. I have already spoken of this in 

 Diagram III. ; but it is much more distinctly observed in Dia- 

 gram IV. Beginning at 112° F., the temperature rises suddenly 

 till at 20 feet from entrance it attains 195° F., whilst the tempe- 

 rature is for the most part from 195° to 199° F. After 90 feet 

 from entrance of chamber it falls at an almost regular amount 

 of 20 degrees for each 10 feet of chamber length, until at 140 

 feet from entrance of chamber the temperature is 120° F. 



Here, then, we have an example of almost perfectly suitable 

 temperature. At this time also the yield of vitriol obtained 

 from this chamber was as nearly the theoretical amount as could 

 practically be obtained; and it was found that whenever the 

 temperature of the chamber was allowed to increase or diminish 

 the result was bad. At this time the amount of nitric acid esca- 

 ping was almost nil, whilst the colour of the liquid coming from 

 the Gay-Lussac tower" showed that the gas escaping was really 

 NO 2 with a scarcely appreciable amount of nitric acid. (I may 

 say here that whenever the colour of this liquor is of a dark red 

 colour, it is a sign of the escape either of nitric acid or some of 

 the higher oxides of nitrogen.) 



The conclusions I draw from these and the preceding investi- 

 gations may be summed up thus : — 



1. The best form of chamber to be employed is one which is 

 long and not high, the analyses pointing to one of somewhat 

 the following dimensions — 150 feet long, 25 or 30 feet wide, 

 and about 10 or 12 feet high. We have thus a large condensing 

 surface, the mixed gases coming readily into contact with all 

 parts of the chamber, whilst they are also in contact with 

 the previously condensed acid which rests on the sides of the 

 chamber. 



2. The temperature of the chamber should be kept as nearly 



