CHEDDAR CHEESE 



319 



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Two c.c. of chloroform fairly accurately measured are placed in 

 the tubes. It is probably better to deliver the chloroform from 

 a burette than to attempt to draw it up in a pipette. On top 

 of the chloroform are added approximately 20 c.c. of the 0.25 

 per cent solution of acetic acid. The tempera- 

 ture of the acetic acid solution should be as 

 near 70 F. as is practicable. A low tempera- 

 ture tends to give a high reading, while a 

 high temperature depresses the volume of the 

 casein. Five c.c. of milk, accurately measured, 

 are next introduced into the tube ; every pre- 

 caution should be taken to have the sample 

 represent as nearly as possible the whole lot 

 of milk from which it is taken. The tempera- 

 ture of the milk should be from 65 to 75 F. 

 After the introduction of the milk the thumb 

 is placed over the neck of the tube, the tube 

 inverted by rotating the hand in order to bring 

 the chloroform down into the barren part of 

 the tube, and the whole then shaken with 

 reasonable vigor for 15 to 20 seconds. This 

 should be timed by the watch. The purpose 

 of shaking is to break up the chloroform mass 

 and bring it into intimate contact with the fat 

 globules, thereby dissolving them. If the shaking is continued 

 for too long a time, a partial emulsion is effected, with a tend- 

 ency toward a high reading and a very ragged reading line 

 between the chloroform and the casein. After shaking, the 

 tubes can be placed immediately in the centrifuge, or when 

 a great number are being run, can be allowed to stand until 

 the same process has been repeated on the others. It is 

 better to prepare all the tubes with the chloroform acetic acid 

 mixture, then introduce the milk and proceed with the shak- 

 ing on the whole series, than to prepare each tube singly. The 



FIG. 58. 

 Special test bottle 

 for the Hart casein 

 test. 



