Quantitative Analysis is the determination of the quantity of all or some of the elements present in a known weight of the compound examined. In inorganic chemistry two methods - volumetric and gravimetric - are usually employed. In the latter the element required is separated in the form of some compound, usually insoluble, which can be thoroughly dried by heating, and the weight of which can be determined. In the volumetric method use is made of some reaction which takes place on the addition to the solution to be examined of another standard solution, of which reaction the end point can be determined. Thus if an acid has to be determined, a solution containing a known quantity of alkali is added slowly. Some litmus is also placed in the vessel, and is of a red colour, but as soon as the quantity of alkali added is just more than sufficient to neutralise the acid the litmus is turned blue. From the quantity of alkali added then the amount of acid present is determined. In organic analysis the estimation is usually performed by combustion, the carbon and hydrogen being completely oxidised to carbonic acid and water and the weight of these substances determined. Other elements present require other and special treatment.