FOOD STUFFS. 45 



2. Milk contains fat, sugar, and proteids. 



Proteids. Heat about 50 c.c. of milk in a flask to 50? C., add two 

 to six drops of dilute sulphuric acid (25 percent.) and shake ; the milk curdles ; 

 strain off the coagulated casein (curd) through muslin. 



b. When milk is filtered under pressure through a porous disk, its casein, 

 being particulate, remains behind. The clear filtrate contains lactose 

 (milk-sugar) and salts. 



c. The strained liquid from a (whey) contains lactose, which, like dextrose, 

 reduces metallic oxides. Apply the copper test ( i, 8). 



d. The coagulated casein contains much fat (butter) which can be extracted 

 by ether. The ether extract when evaporated on paper leaves a greasy stain. 



e- Butter. Repeat i, loandii. Butter yields a small percentage of 

 volatile acid. 



3- Flour. Wash about a dessert-spoonful of sound flour in a muslin bag. 



a. A milky liquid passes through containing much starch ( i, 3) but no 

 sugar ( i, 8). 



b. After washing for some minutes, a sticky and tenacious material remains 

 on the muslin, which can be collected ; this after further washing forms an 

 elastic mass (gluten) which can be drawn out into threads, and on burning 

 gives off the smell of burnt feathers characteristic of a proteid. 



4. Bread. Digest with warm water. The extract contains starch ( i, 3) 

 and dextrose ( i, 8). The residue consists principally of starch and gluten. 



III. Albumin and its Acid and Alkaline Modifications, 



1. Albumin. White of egg (albumen) when diluted with water, strained 

 and filtered, yields a faintly opalescent liquid. This liquid contains a proteid 

 body, albumin, which diffuses through an animal membrane with great 

 difficulty ( ix, 8). 



2. Such a liquid, containing five per cent, of albumen, is to be used in the 

 following experiments. It coagulates on heating at about 70 C. if neutral. 



3. To some of the liquid add a few drops of 0*1 per cent, solution of caustic 

 potash, and warm gently for two or three minutes. Boil. The liquid will no 

 longer coagulate, the albumin having been transformed into the alkaline modi- 

 fication (alkali-albumin or casein). 



4. In a similar way treat another portion with a few drops of very dilute 

 sulphuric acid (o'l per cent.). Warm very gently for not less than five 

 minutes. On boiling no coagulation occurs, the albumin having passed into 



its acid modification (acid-albumin, syntonin). 



5. Cool some of the liquid obtained in 3. Colour it with litmus solution, 

 and add carefully very dilute acid. A precipitate falls on neutralization which 

 is soluble in excess of acid. 



6. Make a similar experiment with the liquid obtained in 4, substituting 

 weak solution of potash for weak acid. A similar precipitate occurs on neu- 

 tralization, which is soluble in excess. 



7. Take three portions, of 5 c.c. each, of the original liquid in three test- 

 tubes, and colour them with litmus. Dilute the O'l per cent, acid about 5 



