NITRATES FROM ATMOSPHERE SCOTT. 365 



The liquid trickles down through the quartz, and meeting the 

 nitrogen peroxide gas, combines with it. The liquid moves from 

 tower to tower in the opposite direction to the gas. Thus the fresh 

 water enters at top of the fourth tower, it flows down through the 

 interstices between the pieces of quartz and falls into a granite tank. 

 From there it is pumped by compressed air to the top of the third 

 tower, down which it trickles into another tank, and from which it is 

 pumped to the top of the second tower, and so on. 



"When the liquid reaches the bottom of the first tower it contains 

 about 40 per cent nitric acid. 



Recently some very remarkable results have been obtained by im- 

 proving the material with which these towers are filled. By using 

 special forms of earthenware instead of quartz, the towers can be 

 reduced in size considerably, and as the cost of the towers is usually 

 about four times the cost of the filling material: this means much 

 cheaper towers. 



The chemical equations are as follows : 



In the electric furnace from 3,000° C. down to 1.000° C, nitric 

 oxide, a colorless gas, is formed — 



N2+0,=:2NO (nitric oxide). 



In the oxidation chambers, etc., from 500° C. down to 50° C, the 

 red-brown gas nitrogen peroxide is formed — 



2NO+02=2NO. (nitrogen peroxide). 



In the four acid absorption towers the nitrogen peroxide combines 

 with water to form nitric acid and nitrous acid — 



2N0„H-R,0=HN0+HN0, (nitrous acid). 



As the nitrous acid is unstable in an aqueous solution it gives nitric 

 acid and nitric oxide — 



3HNO,+H,0=HN03-f2NO (nitric oxide). 



The nitric oxide then combines with more oxygen to form again 

 nitrogen peroxide, and the above equations are repeated — 



2NO-fO,— 2NOo (nitrogen peroxide). 



What is left of the nitrogen peroxide and nitric oxide gases pass 

 to the fifth tower, when they meet sodium hydroxide to form sodium 

 nitrite — 



N02-hNO+2NaOH=H.04-2NaNO (sodium nitrite). 



" The nitric acid of 40 per cent solution is sprayed onto calcium 

 carbonate, and the carbon dioxide gas is driven oflF, leaving calcium 

 nitrate — - 



2HN03-f-CaC03=CO,+H,0+Ca (NO3) ,. 



