320 Eepokt of the Department of Chemistry of the 



Acid casemates of ammonium, sodium and potassium. — In the 

 manner described above, we made numerous determinations in the 

 case of preparations of base-free casein dissolved in the hydroxide of 

 ammonium, sodium and potassium, respectively. Tabulated below, 

 we give the average results of many such determinations. : 



Table IV. — Relation of Alkali Bases to Casein in Acid Caseinates. 



Amount of rr- HCl 



required to cause first 



sign of permanent 



precipitation. 



Cc. 

 Between 44.25 and 44.50 



Amount of alkali left 

 combined with casein. 



60. 



Cc. 

 5.5to5.75 



N_ 

 10. 



Cc. 

 1.1 to 1, 



15 



Amount 

 of ,^ HCl 



required 

 to pre- 

 cipitate 



all of the 

 casein. 



Cc. 

 50 

 50 

 50 



The results in this table indicate that 1 gram of casein forms a 

 soluble compound with ammonium, sodium and potassium, when 

 combined with amounts of each somewhere between 1.10 x 10 ■* and 

 LlSxlO"** gram equivalents of alkali; or, expressed in another 

 form, 1 cc. of ^ alkali combines with an amount of casein somewhere 

 between 0.87 and 0.91 gram. The proportion of basic element in 

 each compound is approximately the following: NH4, 0.20 per ct. ; 

 Na, 0.26 per ct.; and K, 0.44 per ct. Caseinates combining with the 

 amount of alkali base indicated contain the smallest laiown amount 

 of base, according to our present knowledge. It seems proper, 

 therefore, to suggest that such compounds be called mono-basic 

 caseinates. 



Preparation of mono-ammonium caseinate. — It seemed desirable 

 that we should carry the work somewhat farther and prepare one 

 pure compound, at least, in dry form for study. The ammonium 

 compound was chosen as the one offering least difficulty. The 

 method of preparation was as follows: In 2 liters of distilled water 

 containing 250 cc. of 1^ NH4OH, 25 grams of base-free casein were 

 dissolved. After solution was complete, we slowly added 125 cc. 

 of ^ HCl, care being taken to agitate the mixture during the addi- 

 tion of the acid, in order to prevent premature precipitation of any 

 casein. There was next added very cautiously ^ HCl until a per- 

 manent precipitate began to appear, as shown by centrifuging the 

 mixture. The solution was then filtered and measured. The 

 amount of ^ HCl required to precipitate the casein completely was 

 determined in an aliquot part. Then one-third of this amount was 

 added to insure the presence of only mono-basic caseinate. Any 

 precipitate formed was removed by filtration and the filtrate was 

 dialyzed until the ammonium chloride that had been formed in the 



