Identification of Organic Compounds. 15 



Fig. 1. 



Fig. 1), the ethereal layer will be found to have dissolved 

 a large part of the malonic acid, from which it will 

 separate on evaporation, whilst the sodium 

 chloride will remain in the aqueous layer. By 

 repeating the extraction of the aqueous layer 

 with fresh quantities of ether, practically the 

 whole of the malonic acid can be removed. On 

 evaporation of the aqueous solution after re- 

 peated extraction with ether, the salt can be 

 obtained practically free from malonic acid. 

 The malonic acid and salt separated in the 

 above manner can be finally purified by the 

 process of recrystallization. 



The next question which arises is, How 

 can it be definitely ascertained whether a given 

 product obtained by any of the processes de- 

 scribed above is a chemical entity free from any 

 admixture ? Now it has already been stated that the 

 majority of the simpler organic compounds melt when 

 heated, and this melting takes place at a certain 

 definite temperature, known as the "melting point." A 

 small admixture of a foreign organic substance will tend 

 to alter very appreciably (generally to lower) this melting 

 point. Furthermore, with a pure substance, the melting 

 point must be sudden ; at a given temperature the whole 

 sample melts to a homogeneous mass, and if on raising 

 the temperature after the greater part has melted, unmolten 

 crystals can still be observed, this will indicate that a 

 mixture is present. When a substance is perfectly pure 

 and homogeneous, it should not only melt sharply at a 

 given point, but the melting point should show no altera- 

 tion after the substance has been recrystallized from a 

 suitable solvent. The melting point is usually determined 

 by placing a small amount of the sample in the lower end 



