448 FOODS AND FOOD ADULTERANTS. 



around the tube in both directions. Care should be exercised that at 

 the end of this operation the bulb of the thermometer should hang as 

 near as possible in tke center of the crystallizing mass. Directly the 

 above operation is accomplished the mercury will be seen to rise and 

 this rise of temperature will continue for some time, after which the 

 mercury will remain stationary for one or two minutes. The highest 

 point reached is taken as the true temperature of crystallization. 



(g) Melting point of the fatty acids. The melting point of the fatty 

 acids can not be determined in the same apparatus and by the same 

 methods as those described for the fats themselves, because the acids 

 are soluble in alcohol. It should be remembered that the melting point 

 of the fatty acids is slightly above that of the glycerides, and the first 

 determination in every case should be solely for the purpose of deter- 

 mining approximately the temperature at which the fat melts. 



METHOD OF DETERMINING MELTING POINT OF FAT ACIDS. 



(1) By capillary tubes. The fat acid in a capillary tube is placed in a 

 beaker of water, together with a delicate thermometer. The water is 

 slowly heated and the point at which the fat becomes transparent is 

 noted. 



(2) In a closed flask. This method, easy of application and giving 

 satisfactory results, was proposed by Mr. Oma Carr. 



The bulb of a delicate thermometer is coated with the fat acid, and 

 the thermometer, by means of a cork is fastened in a round flask of 

 250cc capacity. The bulb of the instrument should occupy as nearly 

 as possible the center of the flask. The cork should have an air pas- 

 sage for the equalization of the pressure. The flask is slowly heated in 

 a current of warm air, or otherwise, and as the melting point is ap- 

 proached a rotatory movement is given to it. When the fat melts it is 

 seen to collect in a small drop on the lowest part of the bulb, remaining 

 stationary while the flask is turned. The thermometer is best held 

 horizontal!}-. 



(c) Color reaction. The re-agents used in determining the color re- 

 actions were sulphuric acid of a specific gravity 1.7 and strong nitric 

 acid. The method of working with sulphuric acid is as follows : A por- 

 celain plate with trough like indentations, such as is used by artists in 

 mixing paints, is employed. The plate is warmed to a temperature 

 slightly above that of the fat to be examined, and inclined slightly so 

 that the liquid fat may remain in the lower end of the trough. A few 

 drops of the fat are placed on the dish, which is capable of holding 

 several samples; a few drops of the sulphuric acid arc next placed upon 

 the samples of fat and each one stirred with a short glass rod. The col- 

 oration produced is carefully noted, the beginning oi' the change in color 

 noticed and its progress watched. The samples should also be allowed 

 to remain lor twelve hours and the coloration produced at the cud of 

 that time studied. 



