DAIRY FARMING DAIRYING. 989 



The salts of potash and soda nearly all had a greater or less disad- 

 vantageous effect on the curdling. Sodium hydrate and potassium 

 hydrate had the greatest effect in retarding the curdling, followed by 

 sodium fluorid and potassium oxalate. The retarding action of the 

 carbonates and bicarbonates was somewhat weaker, and these were 

 followed in order by the sulphates and nitrates, which in quite concen- 

 trated solutions did not prevent curdling. Lithium chlorid formed an 

 exception, in that in certain concentrations it slightly accelerated the 

 action of rennet. The salts of sodium and potassium in like molecular 

 quantities differed very little in their action on rennet, although in con- 

 centrated solutions the potash salts were on the average somewhat the 

 more injurious. 



Unlike the salts of the alkali metals the salts of the alkaline earths 

 materially accelerated the rennet curdling. Calcium hydrate and bar- 

 ium hydrate were disadvantageous on account of their alkaline action. 

 The various salts of magnesium, zinc, cadmium, and aluminum in 

 medium concentration were on the whole more frequently beneficial 

 than injurious. 



A number of experiments on the effect of common salt used in dif- 

 ferent proportions in normal and watered milk showed I hat salt accel- 

 erated the curdling in milk strongly diluted with water, although this 

 action was not uniform in the case of different milks diluted to the 

 same extent. The reason for this the author was unable to determine, 

 although it is suggested as probably due to the difference in the salt 

 content of different samples of milk. 



In further experiments on the specific effect of calcium chlorid it was 

 found that the curdling was more rapid and the amount of curd formed 

 during the process of rennet curdling was greater the more lime salt 

 the milk contained and the longer it was allowed to act. Both the 

 transformation of the casein by rennet and the union of the paracasein 

 and lime salts require time; and both of these processes go on more 

 rapidly when they take place simultaneously than separately. The 

 experiments did not determine whether the accelerating action of the 

 lime salts was due alone to the precipitation of the paracasein or 

 whether the lime salts accelerated the transformation of the casein by 

 rennet. 



Alkali was found to decompose reunet, and decomposition was more 

 rapid and complete the weaker the rennet solution, the more concen- 

 trated the alkali, and the longer it acted. The action of acids on rennet 

 was found to be very similar to that of alkali. 



As to the effect of temperature it was found that boiled milk curdled 

 more slowly than raw milk; that an acid reaction increased the resist- 

 ance of rennet to temperature ; that solutions of rennet in glycerin were 

 more resistant to a high temperature than aqueous solutions; that 

 rennet curdling is possible between 10° and 50 to 60° ; and that the ren- 

 net enzym in medium concentration is destroyed by heating for 10 m in- 



