148, 149] Qualitative Examination of Oil Cakes 10 1 



of which injurious substances may be detected. These are 

 given below. 



The taste is the most difficult property of all to give 

 an opinion upon, unless the cake have a distinctly nasty 

 taste, in which case the analyst should make some remark 

 thereon. 



148. Testing Linseed Cakes.— Linseed cake should 

 be rich in mucilage and free from starch. Both of these pro- 

 perties are readily tested. Five grams of the ground sample 

 are weighed out on a rough balance and placed in an 8-oz. 

 beaker. A hundred c.c. of boiling water are poured over 

 the cake, and the pasty mass is stirred for a few moments, 

 then allowed to stand for about ten minutes. A rich linseed 

 cake will, when treated in this manner, settle down into a 

 jelly-like mass, whilst a poor cake will settle down in a 

 more granular state. By experimenting with a few samples 

 the student will readily see the value of this test in judging the 

 mucilaginous properties of the cake. To test for starch, a 

 little of the hot liquor with the cake in suspension is poured 

 into a test tube and boiled smartly for a few moments. It is 

 then cooled down, and when quite cold a few drops of a solu- 

 tion of iodine in alcohol are added. The emulsion should 

 only become slightly blue. If it become dark blue some 

 starchy material is present. 



149- Microscopic Examination. —The student should 

 prepare and mount for himself specimens of the husks of the 

 various seeds occurring in feeding materials, and make him- 

 self familiar with the appearance of each. The following 

 method will be found useful in preparing the husk of the seed 

 for examination : 



Digest a portion (about 5 grams) of the material with dilute 

 sulphuric acid (2 per cent.) on the water bath for half-an-hour. 

 Remove the acid liquid by decantation, and wash several times 



