§ 87. FATTY SUBSTANCES. 125 



bicarbonate to ascertain the point of saturation with mer- 

 curic chloride, and so on in the manner already described. 



The results obtained, however, must be corrected for 

 very dilute or very concentrated solutions of urea, since 

 the standard mercuric solution is adapted for such solu- 

 tions only as contain 2" |„ of urea ; if the solution is more 

 concentrated than this, the yellow color appears prema- 

 turely ; if more dilute, it does not appear so soon as it 

 should. 



If the reaction indicating saturation was obtained with 

 10 c.c. or less of the mercuric solution, subtract the prod- 

 uct of 0.08 into the whole number of cubic centimetres re- 

 quired, from this total quantity ; if the reaction was obtain- 

 ed with less than 15 c.c. but with more than 10 c.c, subtract 

 also, in addition to the above product, the product of 0.06 

 into the number of cubic centimetres required above 10 ; 

 if more than 15 c.c. were required, but less than 20, sub- 

 tract also, from the total amount used, the product of 0.04 

 into the number of cubic centimetres above 15, in addi- 

 tion to the above two products. {Rautenherg^ Fres. Zelt- 

 schrift, 4, 500.) The final remainder, multiplied into 0.01, 

 will give the amount of urea in the 15 c.c. of solution 

 tested. 



In case the solution is more than 2"! ^ strong, then more 

 than 30 c.c. of the standard mercuric solution will be re- 

 quired ; for each cubic centimetre of the standard solution 

 used above 30 c.c, ^l^ c.c. of water must be added to the 

 mixture, before taking out a sample drop to be tested 

 with the paste of sodic carbonate. 



FATTY SUBSTANCES. 



87i Fats are insoluble in water, somewhat soluble in 

 strong alcohol, and very soluble in ether. 



Quantitative estimation. — This is effected by heating 

 the finely divided substance with 2-3 volumes of ether 



