47-50] Estimation of Calcium 31 



a bright red heat for twenty minutes, cooled in a desiccator, 

 and weighed again. This gives the weight as CaO. 



When only small quantities of lime are to be estimated (less 

 than -i gram), the CaO method should be used. For larger 

 quantities the CaC0 3 method is sufficiently accurate. 



47. Calculation. — The calculation is very simple; it is 

 either 



Wt. o f CaCQ 3 x 100 

 Wt. of spar taken 



x -56 = % CaO, 



or 



Wt. of CaO x 100 n _ _ _ 



sijr — f — t"i = % of CaO. 



Wt. of spar taken /u 



ESTIMATION OF CARBON DIOXIDE IN 

 CARBONATES 



48. Substance used. — Iceland spar, CaC0 3 . 

 Methods. — (a) By difference. The carbon dioxide is 



driven off by means of an acid, and the loss of weight caused 

 thereby is estimated 



(If) By direct weighing. The carbon dioxide given off on 

 treatment with an acid is absorbed and weighed. 



49. (a) This method, although capable of giving very good 

 results in the hands of a skilled analyst, is somewhat difficult 

 for a student. Still, since it is frequently used both in com- 

 mercial practice and in technical examinations, it is well that 

 the agricultural student should be familiar with it. 



Several kinds of apparatus are used for this determination, 

 but all are the same in principle. Two are described ; one 

 which is readily fitted up in any laboratory, and a second which 

 must be made by a professional glass blower, but which is 

 obtainable from any manufacturing firm. 



50. Apparatus required.— 1. The apparatus is readily 



