TECHNICAL CHEMISTRY. 317 



more similar questions I am afraid we must at present be 

 content with very general and unsatisfactory replies. One 

 authority, the late Mr. Henry A. Smith, tells us that 

 almost all the sulphuric acid is formed within three feet of 

 the bottom of the chamber, whereas the very elaborate ex- 

 periments of Mr. H. W. Deacon of Widnes seem to prove 

 the exact opposite, inasmuch as he shows that no less than 

 79 per cent, of the total make of the chamber is yielded 

 by the upper three or four feet out of a total height of 

 twenty feet, the chamber being eighty-seven feet long and 

 thirty feet wide. Then again the size of chamber best 

 adapted for the manufacture is as yet undecided, as also, 

 whether one, two, or three chambers should be worked in 

 series. Again, the question of temperature is one about 

 which the opinions of manufacturers differ, some believing 

 that the higher the temperature of the gases is kept, the 

 greater is the yield of acid, the only limiting condition being 

 the solvent action of the gases on the lead, whilst others 

 affirm that the yield of acid is always greater in winter 

 than in summer, and that therefore the cooler you keep your 

 chambers the more acid will you get. 



From what I have said you will see that it is not possible 

 to carry out the continuous process of acid making in the 

 chambers beyond the point at which the acid attains a 

 strength of specific gravity 1'55. "When this strength is 

 reached the acid is allowed to flow away from the chamber. 

 But this acid is not strong enough for most of the purposes 

 for which sulphuric acid is required. In order to obtain 

 a stronger acid, either the arrangement of the Glover's 

 towers, as I have described, must be used, or the chamber- 

 acid must be concentrated in leaden pans over or under 

 which a flame and heated air from a furnace play. The 

 acid being much less volatile than the water, this latter 

 passes away in the form of steam, and the strong acid 

 remains. By this means the acid can be concentrated 

 until it attains a specific gravity of 1 '72, or contains 78 

 per cent, of the real acid. Beyond this degree of con- 

 centration the hot acid begins rapidly to attack the lead of 

 the pans, and it therefore cannot be further evaporated. 

 Even then all concentrated sulphuric acid contains lead in 

 solution, as I can easily show you by pouring some of this 

 clear transparent strong aeid into a glass of water ; you see 



