58 LESSONS IN CHEMISTRY. 



but its sui'face becomes covered with a pellicle or skin, resem- 

 bling the scum which forms on the surface of boiling milk; or, 

 if to the liquid we add a few drops of vinegar, a curd falls to 

 the bottom resembling in appearance the curd of milk, and 

 which analysis shows to be almost similar in composition. 

 The substance which exhibits these characters is named vege- 

 table casein, and sometimes legumin, from its being procured 

 from leguminous plants, that is, those which have the seeds 

 enclosed in a pod, and in which it takes the place that in 

 wheat is occupied by gluten. Like gluten and albumen, it is 

 rich in nitrogen, and also contains sulphur as an essential 

 ingredient.* 



76. Diastase. We have seen that when barley sprouts, it 

 acquires certain properties which are not possessed by the 

 unmalted grain. Chemists can procure from the part of the 

 potato which is attached to the young shoot, and also from 

 generating (or sprouting) barley and wheat, a peculiar prin- 

 ciple which they have named diastase, and which cannot be 

 procured from unmalted grain or from that portion of a potato 

 distant from the shoot. This substance has not been com- 

 pletely investigated, but, like gluten, albumen, and vegetable 

 casein, is rich in nitrogen, and is supposed to be produced 

 by the transformation of some of these compounds. Its 

 effects upon starch are most remarkable, the diastase contained 

 in one pound of malted barley being sufficient to convert five 

 pounds of starch into sugar. 



77. Fatty Matters, Oils, and Vegetable Acids. — In plants 

 there are to be found, in addition to the substances already 

 noticed, certain fatty matters and oils, and also a great num- 

 ber of acid pruaciples, which, though forming usually but 

 u minute portion of their substance, frequently exercise an 



* The following is the composition of the bodies above descril^ed : — 



Albumen. Fibrine. Casein 



Vegetable. Animal. Vegetable. Animal. Vegetable. Animal. 

 Carbon . . 54-74 55-461 54-603 54-686 54-138 54.825 

 Hydrogen . 7-77 7-201 7.302 6-835 7-156 7 153 

 Nitrogen . 15-85 15*673 15.810 15.720 15-672 15-625 



Oxygen. •? 21-64 21-665 22-285 22-759 23-034 22-394 

 Sulphur &c. S 



100-00 100.000 100-000 100-000 100-000 100-000 



