59] Volumetric Estimations 39 



of HC1, and if this amount be made up to a litre with water 

 it will constitute a normal solution of HC1. 



On the other hand, should a dibasic acid be used, only 

 half its molecular weight will be required to make a litre of 

 normal solution, as may be seen from the equation 



H 2 S0 4 + 2KHO = K 2 S0 4 + 2H 2 



98 + 56x2 = 135 +2x18 



Ninety-eight grams (or the molecular weight in grams) of 

 H,S0 4 will neutralise 56x2 grams of KHO, or 2 litres of 

 normal KHO. 



In the same way, a normal solution of oxalic acid, 

 C 2 H 2 4 .2HoO, will contain 126-^-2, or 63 grams per litre. 



As normal solutions are often too strong for delicate work, 

 solutions of half normal strength (seminormal), or one-tenth 

 normal strength (decinormal), are frequently used. 



Very little practice will soon show the student that the great 

 advantage which solutions of normal strength, or some simple 

 fraction- of this strength, have over all others is in the facility 

 with which results may be calculated from them. 



59. Indicators. — The following are the principal indi- 

 cators used : 



Litmus. The solution is not often used in agricultural 

 work, but litmus paper is sometimes necessary. This is bought 

 in small strips made up into the form of books, and will be 

 familiar to students who have done any qualitative analysis. 



Cochineal This indicator is not affected in colour by 

 carbonic acid. It may be prepared by dissolving 1 gram of 

 powdered cochineal in 20 c.c. of methylated spirit, diluting 

 with 80 c.c. of water, and allowing to settle. The clear liquid 

 is yellow, but is changed to a deep wine-red by alkalis. It 

 should not be used in presence of iron, aluminium, or acetic 

 acid, or their compounds. 



