The conditions essential to accurate gravimetric analysis have been given. As a rule such estimations come under one of four classes:
These are the most usual and accurate methods of gravimetric analysis. The element sought is precipitated and weighed generally as a compound, definite in composition.
Direct Estimation by Loss
Here the element sought is volatile or forms a volatile compound and is driven off, the weight being taken as the volatilisation loss.
When the previous methods are difficult these are used. If, for instance, Na or K are to be determined, unite them to Cl or SO4, say to the latter, and weigh the joint