QUESTIONS AND PROBLEMS 177 



urine undergoes fermentation, a smell of ammonia is noticed. Illus- 

 trate by an equation the change in the urea that then takes place. 

 63. What is cyanogen, and what element does it particularly resemble ? 

 Illustrate this resemblance by formulae representing the composition 

 of hydrocyanic acid and potassium cyanide. Ferrocyanide of 

 potassium reacts with ferric chloride forming prussian blue. Repre- 

 sent the change by an equation. 



*64. From the quinine supplied prepare a well-crystallised specimen of the 

 sulphate. 



*65. The commercial hydrochloric acid sometimes contains ferric chloride. 

 Dilute and test for iron by the prussian blue test. 



The Albuminoids. 



66. What is an "albuminoid"? Of what elements does it consist, and 

 how may each of these be shown to be present ? 



6t. What is meant by the "coagulation" of albuminoids? Name three 

 methods by which albuminoids may be coagulated, and give ex- 

 amples of each method. 



68. Give instances of albuminoids which exist naturally in the soluble and 



in the coagulated state. Describe the preparation of gluten of 

 wheat, myosin of flesh, and fibrin of blood. 



69. What is understood by the *' peptonisation " of albuminoids, and what 



are the substances capable of producing it ? 



70. Of what is milk composed, and how may its constituents be sepa- 



rated ? 



71. To what is the souring and spontaneous curdling of milk due, and by 



what means may souring be retarded or prevented ? 



72. What are the three data by which the purity of milk is judged, and 



how are they determined ? 



73. Describe the principal chemical changes that take place in seeds 



during germination, and their purpose. State what compounds 

 are absorbed by the leaves and roots of the young plant from the 

 air and soil, what are the substances elaborated in the leaves, and 

 what are the means employed by the plant for their production. 

 Give an equation representing the formation of starch, and state 

 how this substance, produced in the leaves, yet finds its way into the 

 root or seed. 



74. What do you understand by " osmose " and "dialysis " ? Define the 



terms ** crystalloid" and " colloid," and give examples of chemical 

 compounds belonging to both classes. How are albuminoids 

 altered in this respect when converted into peptones? Under 

 what circumstances is "osmotic pressure " exhibited ? 

 12 



