92 MASS. EXPERIMENT STATION BULLETIN 166. 



mating (hydrocarbon) oils they are far more important. The chemical 

 methods are indispensable for determining the identity, composition and 

 qualitj^ of oils and fats, and are treated in a monographical way. 



In standardizing the methods an effort was made to use not only the 

 same flasks but also the same amount of material, volume of solution and 

 indicator, and the same agent to facihtate boiling and like conditions of 

 treatment in so far as possible. All the methods, practically without 

 exception, have been modified in reagents and manipulation, and atten- 

 tion called to numerous precautions found necessary for accurate work. 

 This is especially noticeable in the determination of insoluble acids, 

 unsaponifiable matter and iodine number. The determination of acetyl 

 number should be considered a new method. The process for determin- 

 ing stearic acid is a modification of the Hehner and Mitchell method 

 adapted for use with the insoluble acids of butter fat for which the orig- 

 inal did not prove applicable. The limits of error are original, based 

 chiefly on practical manipulation, although considered on theoretical 

 grounds. The s^'Tlopsis of reaction expresses the successive steps and 

 underlying principle in each process free from verbiage. The supple- 

 mentary notes include any information, original or otherwise, that might 

 be of service in interpreting results. All tables and formulas are calcu- 

 lated on the latest atomic weights, and many formulas express old princi- 

 ples in a new light. 



This article constitutes a portion of a paper submitted for the degree 

 of doctor of philosophy at the Massachusetts Agricultural College. 



CLASSIFICATION — Oils, Fats and Waxes. 



Natural oils may be divided into two major groups, i.e., essential, 

 ethereal or volatile oils, and fatty, fixed or nonvolatile oils. 



The fatty oils may be subdivided according to consistency at ordinary 

 temperature into oils and fats; according to origin, into vegetable and 

 animal; according to properties, into drying, semidrying and nondrying, 

 etc. 



Waxes are generally grouped with the fatty oils on account of their 

 similar chemical structure. Oils and fats are essentially neutral glyceryl 

 esters, compounds of fatty acids and the soluble tribasic alcohol, glycerol. 

 Waxes are composed of esl ers of fatty acids and insoluble monobasic and 

 occasionally dibasic alcohols, together with a considerable proportion of 

 free alcohols and of hydrocarbons. 



Any general classification of oils, fats and waxes, whether of origin, of 

 physical characteristics, or of chemical characteristics, is open to criti- 

 cism; probably that of Lewkowitsch, based on the magnitude of the 

 iodine number correlated with that of consistency, origin and properties, 

 is the best that has been offered. 



