6o6 Jonnial of Agriculture. \"utoria. [loOcx.. 1912. 



considerali!^ resistance to the grinding process. Tliey are generally less 

 bulky weight for weight, as compared with the more friable deposits, 

 and proportionately less likely to disintegrate as readily in the soil. 



Gypsum (Sulphate of Lime). 



Besides the natural deposits obtainable as carbonate of lime, consider- 

 able depcsits exist of gypsum. Gypsum is lime (CaO) in combination 

 with one part of sulphuric acid (H2SO4) and two of water (HgO). It 

 possesses the following formula: — 



CaSO^ • 2H.,0 

 The molecular weight being : — 



Sulphate of ^^j , Oxide of Calcium Sulphuric ,,. 



Calcmm. nmie). Anhydride. 



CaSO^ . 2H.p = CaO + SO3 + 2H2O 



172 56 80 ^6 



therefore as 172 : 100 : : 5^ : the percentage of lime (CaO) 



56 X 100 



172 



32.51 CaO 



Thus, 100 lbs. of gypsum will yield 32.54 lbs. of lime. Gypsum 

 being already in combination with an acid (H-0SO4) does not possess the 

 power of combining with and neutralizing the acids in. the soil, so that 

 it is useless as a dressing for sour land. Furthermore, as its lime con- 

 tent is only about one-third that of lime as shown above, its claims to 

 recognition as a substitute for burnt lime can only be reasonably enter- 

 tained when the price and convenience of the deposit are such as to 

 counter-balance the extra cost of handling, rail, carriage, &c. 



The Relative Value of the Different Forms of Lime. 

 56 li)s. of fresh burnt lime contains the same amount of lime as — 



56 lbs. of fresh ground lime. 



74 lbs. of water-slaked lime. 

 100 lbs. of carbonate of lime (as a powder — ground limestone, 



chalk, &c.). 

 100 lbs. of old air-slaked lime. 

 172 lbs. of sulphate of lime (as gypsum). 



The equivalent value is. therefore, as follows: — 

 100 lbs. of fresh burnt lime is equivalent to — 

 135 lbs. of water-slaked lime. 

 178.6 lbs. of carbonate of lime (as a powder). 

 307.3 lbs. of sulphate of lime (as gypsum). 



Standards. 



Zime. A good quality lime should contain at least 85 per cent, com- 

 bined oxide and carbonate, of which not more than 10 per cent, shall 

 be present as carbonate. 



Slaked Lime. — A good quality slaked lime should contain at least 

 85 per cent, of combined oxide, hvdrate, and carboi ate. of which not 

 more than 10 per cent, .shall be present as carborate. 



