AMIDES ALKALOIDS. 219 



figures of such analyses. In the modern analyses a distinc- 

 tion between the two classes of nitrogenous ingredients of food 

 is made, and chemical analysis and experimental feeding agree 

 much more nearly. 



Both amides and albuminoids yield their nitrogen as ammo- 

 nia when treated by the Kjeldahl process (v. Chap. V., p. 93.), 

 and the total nitrogen obtained by the application of this process 

 to the food stuff is first estimated. In order to determine the 

 amount of nitrogen present as amides either of the two follow- 

 ing methods may be used. 



1. A w r eighed quantity of the material is boiled for half an 

 hour with 5 % solution of hydrochloric acid or sulphuric acid. 

 The albuminoids are not affected, but the nitrogen of the 

 amide group is thus converted into ammonium chloride or 

 sulphate, e.g.: 



2 [CO(NH a ).C a H(NH a ).COOH] + 2H 4 



Asparagine. 



Amido-succinamic acid. 



= 2 [C a H 8 (NH a )(COOH)J + (NH 4 ) a S0 4 



Aspartic acid. 

 Amido-succinic acid. 



The solution is then exactly neutralised with sodium carbonate 

 and distilled with magnesia, the ammonia evolved being 

 received in standard acid. Half the nitrogen contained in 

 asparagine is thus obtained as ammonia. It is usual to report 

 all the amide nitrogen in terms of asparagine. 



2. A weighed quantity of the food is treated with water 

 containing freshly precipitated, well-washed copper hydroxide, 

 filtered and washed ; the amides pass into solution ; a nitrogen 

 determination by the Kjeldahl process in the residue gives a 

 measure of the true albuminoids. 



The Alkaloids. These substances are nitrogenous bases, 

 possessed usually of powerful therapeutic properties. They 

 are very numerous and in constitution are generally to be 

 regarded as derived from ammonia, NH 8 , by the replacement 

 of a part of or all the hydrogen by complex groups. With few 

 exceptions, e.g., nicotine, coniine, and sparteine, they contain 

 oxygen. They exist in the plant probably as salts of organic 

 acids. They are only slightly soluble in water, more so in 



