16 



which it is converted into lactic acid by various orj^anisms. (See Lec- 

 ture 6, paragraph 1.) Experiment — see page 17. 



5. Salts. — The saUs of milk, also called mineral matter or ash, are 

 present in small (piantities, but are very important. The relation of 

 the lime (calcium) salts to cheese making will be pointed out later. 

 (Lecture 9, paragraph 3.) 



6. Galactase. — (wSee Lecture 6, paragraph 5.) 



7. Amounts of constituents in milk of representative cliaracter. — (a) 

 The average of 5,552 American analyses of milk compiled by the 

 writer is as follows: Water 87.1 per cent, total solids 12.9 percent, 

 fat 3.9 per cent, calcium casein 2.5 per cent, albumin 0.7 per cent, 

 sugar 5.1 per cent, and ash 0.7 per cent. 



(b) Variation in composition of cheese-factory milk during the sea- 

 son (May to October). 



In the following table are given the lowest, highest, and average 

 results for the composition of milk during the cheese-factory season: 



Vanations in composition of milk. 



EXPERIMENT AND PRACTICE WORK, FIRST LECTURE. 



Time required for experiments. — The work prescribed in these experi- 

 ments will require from one to two hours of continuous work, according 

 to the facility of individual s,tudents in performing the manipulations. 

 As indicated, a part of the work will be carried over until the day fol- 

 lowing for final observation. 



Apparatus required. — (1) Pipette or graduate to hold 10 cubic centi- 

 meters, (2) teacup or glass tumbler or test tube or beaker, (3) common 

 sal soda, (4) whey, and (5) microscope and accessories. 



1. Action of acids on calciuin casein (casein) of milk. — To 10 cubic 

 centimeters of sweet milk in a teacup or glass add 100 cubic centimeters 

 of water. Warm to 100° F. and add some strong vinegar (impure 

 dilute acetic acid) drop by drop," shaking or stirring vigorously. Con- 

 tinue to add vinegar and agitate until a white, solid substance sepa- 

 rates. This substance is casein acetate, formed by the union of the 

 acetic acid and the casein of the milk, and it is insoluble in water. 

 Pour off the water from the solid white substance and then add care- 

 fully about 15 or 20 cubic centimeters of sulphuric acid such as is used 

 in Babcock test. What happens to the wliite substance (reference 

 No. l,p. 21)? 



