NITRATES FROM ATMOSPHERE — SCOTT. 375 



stairway fashion. The acid is also heated by direct contact with hot 

 gases which come from the furnace. These gases are thus charged 

 with water and nitric-acid vapor. 



To condense the acid the gases are passed through a cooling coil 

 of stoneware, which offers a large cooling surface. The remainder 

 of the gases then pass to the oxidation tower and mix with those 

 coming from the furnace. 



The acid obtained by the process is 36° Beaume and contains r)0 

 per cent HNO.,. The concentration can not go beyond 60 per cent 

 by this process, because the vapor produced has a concentration 

 which increases with the concentration of the solution, and for 66 

 per cent the vapor produced has exactly the composition of the 

 liquid. 



To obtain higher concentration other processes nnist be resorted 

 to, and as high as 98 per cent can be obtained. 



Some idea of the efficiency of the plant may be obtained fi'om 

 the fact that Mr. Pauling giiarantees 60 grams of 100 per cent HNO.. 

 per kilowatt-hour of electrical energj'^, measured at the entrance of 

 the electric transmission line into the factory; and also that the 

 electrochemical plant proper will cost about 120 francs (£5) per 

 kilowatt. 



The Southern Electro- Chemical Co., of Nitrolee, S. C, in the 

 United States, has a 4,000-horsepower plant on the Pauling system 

 for manufacture of calcium nitrate. Electric energy is generated in 

 two water-power plants at Great Forks and Eocky Creek. 



CATX'IT'M CYANAM 11 )K. 



The discovery of calcium cyanamide came about as the result of a 

 research by Dr. Franck and Dr. Caro, who were following on the 

 lines of some previous work of Playfair and Bunsen. Their imme- 

 diate object was to make cyanide of potassium for the recovery of 

 gold from tailings, and they incidentally found that barium carbide 

 absorbed nitrogen to form barium cyanamide. By using calcium 

 carbide ihej obtained a similar reaction, according to the formula — 

 CaC,+2X=CaCX,+C 



It was then found that by treating calcium cyanamide with hot 

 water it gave off ammonia according to the equation — 



CaCNo+3H,0=CaCo3+2 (NH3) , 

 and this gave rise to the idea of using it as a manure. 



As carried out at the Odda Works the calcium carbide broken into 

 lumps is delivered to crushing machines, from which it passes to 

 mills in which it is ground fine, the whole of these operations being 

 effected automatically in an air-tight plant so as to prevent acetylene 

 gas being given off. It is of interest to note that the glowing mass 

 from the calcium carbide furnace can not be used straight aAvay. 



