MILK, FLOUR, AND BREAD. 73 



(a.) Using the nitrate of 6 (a.) add magnesia mixture 

 Lesson XI V., 6 (g.) i.e., ammonio-sulphate of magnesia, 

 which gives a precipitate of phosphates. 



(b.) Silver nitrate gives a precipitate insoluble in nitric 

 acid, indicating chlorides. 



8. Boil milk in a porcelain capsule for a time to cause evapora- 

 tion. It is not coagulated, but a pellicle of insoluble casein forms 

 on the surface. Remove it and boil again ; another pellicle is 

 formed. 



9. Opacity of Milk. Vogel's Lactoscope. 



Apparatus required. A graduated cylindrical cc. measure 

 to hold 200 cc. ; a lactoscope, with 

 parallel glass sides, 5 mm. apart (Fig. 

 14); a burette or pipette, finely 

 graduated ; a stearin candle. 



Method. (a.) Be certain, by micro- 

 scopical examination, that the milk Fig. 14. Lactoscope. 

 contains no starch, or chalk, or other 

 granular impurity. 



(b.) Place 100 cc. of water in the cylindrical measuring 

 glass, and add 3 cc. of milk. Mix thoroughly. 



(c.) In a dark room place the lactoscope on a table, and 

 1 metre distant from it a lighted stearin candle. Fill the 

 lactoscope with the diluted milk, and look at the candle 

 flame through the glass. If the contour of the flame can 

 be seen distinctly, pour back the diluted milk into the bottle, 

 and add another 3 cc. of milk. Mix again. Test the mix- 

 ture again, and repeat until, on looking through the glass, 

 the outline of the candle flame can no longer be recognised. 

 Add together the quantities of milk used. An empirical 

 table constructed by Vogel, gives the percentage of fat. 



10. Wheaten Flour. 



(a.) Gluten. Moisten some flour with water until it forms 

 a tough tenacious dough ; tie it in a piece of muslin, and 

 knead it in a vessel containing water until all the starch is 



