136 LABORATORY LESSONS IN GENERAL SCIENCE 



(a) In a spoon heat in turn small pieces of each substance, 

 stirring them with a match stick as they boil. Note which 

 boils with much foam and which with much sputtering. 



(6) Note the differences in results as the substances are 

 tested separately as follows : Put a small lump into a test 

 tube one fourth full of milk, and heat till the lump is melted ; 

 then stir the liquid with a long splinter of wood, cooling the 

 tube under the faucet till the fat hardens. In one case 

 the fat should collect in a mass that can be removed on the 

 splint, and in the other cases it remains scattered in gran- 

 ules throughout the milk. 



Summarize the results by which any one of these sub- 

 stances may be identified with a reasonable degree of cer- 

 tainty. 



5. What per cent of butter-fat should be present in 

 milk ? What per cent of milk is water ? What preservatives 

 have been most commonly used in milk? Wherein is the 

 harm? What causes the souring of milk by natural pro- 

 cesses? How is this ordinarily delayed in household uses? 



6. What is (a) condensed milk, and its especial worth; 

 (6) sterilized milk; (c) Pasteurized milk? 



7. Observe results closely, and state what is noted as 

 the teacher (a) adds to one fourth test tube of milk a little 

 vinegar, warming and shaking till separation of curd and 

 whey occurs; (6) tests some of the curd with nitric acid, 

 and then with ammonia solution, for protein food material. 



8. Describe briefly the making of cheese. Mention 

 various kinds of cheese, and the differences in their manu- 

 facture. 



