IN POPULAR CHEMISTRY. 



101 



23O tons of iron pyrites containing 37.5 per cent, of 



sulphur ? 



(See Cfiemistry, p. 158.) 



3?i % of 230 = 86.25 tons, the weight of S contained in the 

 pyrites. 



S : FeSO 4 , 7H 2 O : : 86.25 : x. 



32: 278 :: 86.25 : x. 



x = 749.296 tons of FeSO 4 , 7H 2 O. 



50. Required 5OO tons of soda crystals; what willbe 

 the weight of salt and pure sulphuric acid needed ? 



Find (1) how much Na there is in 500 tons of "soda," and 

 (2) how much NaCl would be needed to furnish that amount of 

 the metal in case all were utilized. 



(1.) Na 2 : Na 2 CO 3 , 10H 2 O : : x : 500 tons. 

 46 : 286 : : x : 500 tons. 



286 x 23,000 tons. 



x = 80.42 - tons (Na). 



(2.) Iff of any amount of NaCl is Na ; hence, to furnish 

 80.42 tons of Na would require ff|x80.42 tons = 204.546 tons 

 (Nad). 



(3.) By comparing the atomic weights of the substances, it 

 will be seen that for 46 parts of Na there must be 98 of pure 

 H 2 SO 4 . ft x 204.546 tons = 435.771 tons (H 2 SO 4 ). 



51. Describe the uses of lime in agriculture. 



Lime acts in various ways to improve the fertility of a soil. 

 It corrects its acidity, aids in the decomposition of the rocky 

 constituents, hastens the decay of the humus, and also makes 

 the soil more porous. It does not, however, benefit the grow- 

 ing plant directly, but works up other materials in the soil. It 

 therefore loses its effect after a time. 



52. Hoiv many tons of oil of vitriol, containing 7O per 

 cent, of pure acid (Jf 2 O 4 ), can be prepared from 25O tons 

 of iron pyrites, containing 42 per cent, of sulphur ? 



(1.) (See Question 49.) 250 tons x. 42 = 105 tons (S). 

 (2.) S : H 3 SO 4 : : 105 tons : x. 

 32 : 98 : : 105 tons : x. 

 32 x = 10,290 tons. 



x = 321.56 tons (H 8 SO 4 ). 



