414 ANNUAL. REPORT OF THE Off. Doc. 



two absorption systems in parallel at the factory. Each row or 

 system is composed of two granite and two sandstone towers filled 

 with quarts which is being drenched, or kept moist, by slowly 

 trickling water, which takes up most of the nitric acid present in 

 the air current. A fifth tower in each system or series is filled 

 with ordinary bricks, which are kept moist with milk of lime. This 

 lime takes up the rest of the nitric and nitrous acid gases, and forms 

 calcium nitrate and calcium nitrite. 



By a special arrangement of containers at the top and bottom of 

 the towers, the acid liquid from tower number 4 is pumped to num- 

 ber 3, from 3 to 2, and so on, so that the strongest acid is in tower 

 number 1. From there it is removed, having a strength of about 

 50 per cent, acid, and conducted to a row of open granite vats, 

 where it is stored until needed for further treatment. A portion 

 of this acid is used for breaking up the nitrite which accompanies 

 the nitrate of lime in the fifth tower. By addition of nitric acid to 

 the lime mass, containing both nitrate and nitrite of lime, in a 

 closed vessel, the nitrites are broken up and the acid radicle set 

 free and driven back to absorbers again. The reaction which takes 

 place is as follows: 



Ca (N02)2+2 HM)3==Ca (N03)2+HoO-[-N02+NO. 



The lime solution containing the pure calcium nitrate, plus nitric 

 acid, is placed in other vats, mixed with the other acid and netural- 

 ized by adding limestone. This neutralized mass is then evaporat- 

 ed in iron vessels, down to a boiling point of 145° C, which is 

 equivalent to a 75 to 80 per cent, concentration of calcium nitrate, 

 or about 13.5 per cent, nitrogen in the mass. When this point of 

 concentration is reached, it is poured into iron cylinders of about 

 200 liters (about 50 gallons) capacity and cooled. The solution 

 solidifies into a pourous, easily pulverized mass which is ground up, 

 packed in paper lined wooded boxes, and is then ready for the mar- 

 ket. If the neutralized solution is concentrated to a boiling point 

 of 120° C. it will crystallize, and the crystals, freed from the 

 mother liquid by centrifugal force, are the pure calcium nitrate 

 (Ca(N03)2=4HoO), the new nitrogen fertilizer. 



This salt can be made into a iDasic salt, with excess of lime, hav- 

 ing 8 to 9 per cent, nitrogen. This basic salt is not so hygroscopic 

 but remains dry in the air, and is therefore undoubtedly more con- 

 venient for fertilizing purposes than the crystallized nitrate. But 

 the other peculiar form of nitrate, containing about 13.5 per cent, 

 nitrogen as already mentioned, is also less hygroscopic than the 

 crystallized salt, can be handled and sown by machinery, and it is in 

 this form that the new fertilizer appears in the market. By using 

 sodium hydrate in the last absorption tower, instead of lime hy- 

 drate, a mixture of sodium nitrate and sodium nitrite is obtained, 

 and 80 to 90 per cent, of the salt formed may be nitrite which will 

 crystallize out almost pure. Thus a very valuable substance, Na- 

 NO2, may be obtained as a by product. This sodium nitrite is used 

 in making azocoloving stuff. The sodiunf nitrate can also be ob- 

 tained from nitrate by melting it together with lead, according to 

 the following reaction, NaN03+Pb=NaNO.+PbO. The nitrogen 

 can also be recovered from the sodium hydrate solution by treating 

 it electrolytically. According to Cassel, the nitrates and nitrites 

 both form ammonia which is driven over by boiling, and is caught 

 in nitric acid thus forming ammonium nitrate. 



