8 BULLETIN 620, U. S. DEPARTMENT OP AGRICULTURE. 



The first method tried was the ordinary one of burning sulphur 

 and passing the gas through a milk of lime solution. A small sul- 

 phur stove, with a flat bottom and a burning area of about 3 square 

 feet, was designed. The gas, after leaving the stove, passed through 

 a cooling system and through three absorption tanks of about 150 

 gallons capacity, so arranged that it entered the bottom of the first 

 tank, the unabsorbed portion then passed to the bottom of the next 

 tank, and so on to the third one, the gas being moved by suction. 

 The two tanks nearest the stove contained water alone and the last 

 one milk of lime. After the system had been going for about three 

 hours, samples were taken from each tank and analyzed. The 

 liquor in each of the first two tanks contained about 1.20 per cent of 

 S0 2 and in the last tank 3.10 per cent, all of it calcium bisulphite; 

 nor could the solutions be made any stronger by continuing the 

 operation, the gas simply passing through without being absorbed. 

 The reason that the solutions would not become stronger is that the 

 solubility of S0 2 gas depends on its dilution. Pure S0 2 gas is very 

 soluble in water, it being possible to make solutions containing as 

 high as 10 per cent; but just as soon as it is diluted with some other 

 gas that is not soluble in water, such as nitrogen, the strength of 

 the solutions becomes much less. Thus, the gas produced here con- 

 tamed about 17 per cent S0 2 and would produce only a certain 

 strength of solution no matter how long the gas was passed through ; 

 the solutions became even weaker if the fire in the burner got low. 

 As solutions had to be made to meet a wide range of concentrations, 

 this method was abandoned. 



It was then decided to absorb the gas in two towers, 15 feet in 

 height and 15 mches in diameter, made of sewer crock, and filled 

 with broken tile, to see how strong a solution could be obtained by 

 absorbing the gas in pure water alone. The gas from the burner 

 entered the first tower at the bottom and met water trickling down 

 through the broken tile, left it at the top, and passed into the bottom 

 of the next tower. The strongest acid in the first tower contained 

 2.20 per cent S0 2 and the second 1.10 per cent. As this acid was not 

 strong enough, it was decided to pump the acid from the towers 

 into the digesters, there drive off the gas by heat and reabsorb it in 

 one of the tanks. While acid by this method could be brought to 

 any desired strength, it took so much time and attention that it 

 was not practical. 



The next method tried was to secure the action of sulphuric acid 

 upon sodium bisulphite according to the equation 2NaHS0 3 + H 2 S0 4 = 

 Na 2 S0 4 + 2S0 2 + 2H 2 0. For this purpose, a 16-inch pipe, 4 feet long, 

 was flanged at both ends and lead-lined. The desired amount of 

 sodium bisulphite mixed with water was fed in through an opening 

 in the upper flange, which was then closed. The sulphuric acid was 



