292 Report of the Department of Chemistry of the 



soluble calcium increases; (2) this increase is largely due to reaction 

 of sodium citrate with the calcium caseinate in the milk, forming 

 sodium caseinate or a double salt (calcium-sodium caseinate) and 

 calcium citrate; and (3) use of increased amounts of sodium citrate 

 lengthens the time required for the milk to curdle with rennet action 

 or entirely prevents the curdling. 



Table II. — Effect of Sodium Citrate on the Curdling of Milk by Rennin. 



CONCLUSION. 



Without going into full details, it will answer our purpose here 

 to offer, on the basis of the facts developed, the following explanations 

 as to why the presence of sodium citrate in milk delays or prevents 

 curdling by rennin : Knowing the amount of soluble calcium formed 

 by addition of sodium citrate to milk and knowing also the amount 

 of casein present, we are able to ascertain that, at the point at which 

 the rennet solution fails to curdle the milk, we have in place of the 

 calcium caseinate of the normal milk a double salt, calcium-sodium 

 caseinate. This double salt, on addition of rennin, forms a calcium- 

 sodium paracaseinate containing one equivalent of sodium; and this 

 compound, owing to the presence of the sodium, is not curdled by 

 rennin. The increasing softness of the curd, accompanying the 

 addition of increasing amounts of sodium citrate, is due to the presence 

 of increasing amounts of calcium-sodium paracaseinate. A point is 

 finally reached when all the calcium caseinate becomes calcium-sodium 

 paracaseinate and the milk fails to curdle. 



