206 APPENDIX. 



Heat. All are coagulated by boiling, except peptones. 



Xanthoproteic Reaction. A solution boiled with 'strong nitric acid 

 becomes yellow : the color is deepened by the addition of ammonia. 



Biuret Reaction. "With a trace of copper sulphate and an excess of 

 potassium or sodium hydrate they give a purple reaction. 



Millons Reaction. With a solution of metallic mercury in strong 

 nitric acid (Millon's reagent) they give a white or pinkish reaction, and 

 the color becomes more pink on boiling. 



FOR STARCH: 



Iodine Reaction. Add to a solution of starch a small quantity of 

 tincture of iodine, and a blue reaction results. The color disappears on 

 heating and returns on cooling. 



Glycogen. Same test gives reddish reaction, port- wine color, which 

 disappears on heating and returns on cooling. 



FOR SUGAR (GLUCOSE) : 



Moore's Test. Boil solution of sugar with an excess of potassium 

 hydrate, brown color-reaction. 



Tromniers Test. Add to solution a sufficient amount of potassium 

 hydrate to render it quite strongly alkaline. Then add a solution of 

 copper sulphate, drop by drop, until a distinct blue tinge is visible. 

 Heat, and the presence of sugar is shown by appearance of red, yellow, 

 or orange color-reaction. 



Fehling's Test Solution. An alkaline copper solution by which a 

 quantitative test may be made. The solution is somewhat unstable, and 

 is for this reason to be tested by boiling before using. The strength of 

 the solution is such that 1 cubic cm. (15 minims) will be exactly decolor- 

 ized by -^ of a gramme (.075 grains) of glucose. This test is very 

 delicate, and is quite commonly used for urinary examinations to detect 

 glycosuria. 



The Fermentation Test. If a small quantity of yeast be added to a 

 sugar solution, the fungus of the yeast (saccharomyces) will cause the 

 sugar to be decomposed into carbonic acid and alcohol. If the process 

 be continued until the sugar is entirely broken up. the amount of car- 

 bonic acid evolved indicates the proportion of sugar present. 



FOR BILE SALTS: 



Pettenkofer 1 s Test. Upon the addition of sulphuric acid to a solution 

 of bile-salts in water there is a precipitation of the salts, which are 

 redissolved by a further addition of the acid. If a drop of a solution 

 of cane-sugar be added, a deep cherry color is developed. 



FOR BILE PIGMENTS : 



Gmelins Test. Add a small quantity of nitroso-nitric acid to a solu- 

 tion of the bile-pigments, and a play of colors results, beginning with 

 green and changing to blue, violet, red, and yellow. This is seen best 

 on a white background ; therefore a plate is often used for this test. 



