8 BULLETIN 620, U. S. DEPARTMENT OF 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 bemg moved by suction. 
The two tanks nearest the stove contamed 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 
SO, 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 SO, gas depends on its dilution. Pure SO, 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- 
tained about 17 per cent SO, 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 inches 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 tricklmg 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 SO, and the second 1.10 percent. 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 2NaHSO, + H,SO,= 
Na,SO,+2SO0,+2H,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 
