LARD AND LARD ADULTERATIONS. 



443 



a hood, the side next the window being provided with an opening for 

 admitting the light, and the one next the operator being entirely open. 



The thermometer should rest with its bulb as closely as possible ap- 

 plied to the metallic casing of the prisms of the instrument. The tem- 

 perature marked by it is much lower than that of the space between the 

 prisms occupied by the film of oil under examination. For purposes of 

 comparative readings a cotton oil is used, the refractive index of which 

 is carefully determined at 25. 



When the temperature of the refi actometer on the air bath has become 

 constant, the same cotton oil is placed on the prisms, and after waiting 

 for 10 to 20 minutes for the same temperature to be established, the 

 index at that temperature is read off. The lards, stearines, etc., are 

 then examined at that temperature and reduced to the standard of 25 

 by the factor determined as above. After the introduction of each fresh 

 sample the instrument is allowed to stand for 10 to 20 minutes in order 

 to secure a uniform temperature for all the readings. 



Example. 



Cotton oil, No. 6258: 



R.I. at 25 1.4674 



R. I.atN = 1.4565 



Factor, .0109 



External T 49.5 



Calculated internal T= 57.5 



At these temperatures a large number of indices of lards, stearines, 

 fat acids, etc., was taken. 



(e) Rise of temperature. The rise of temperature which fats and oils 

 undergo when mixed with sulphuric acid was determined in the follow- 

 ing manner. The apparatus used is represented in Fig. 22. The idea 

 of this piece of apparatus was derived from a description given by 



