APPENDIX. 835 



(v.) Picric acid test. To the solution about a fourth of its bulk of 

 picric acid (saturated solution) and an equal quantity of caustic potash 

 are added, and the solution is boiled; the liquid becomes of a very deep 

 coffee-brown. 



(vi.) Indigo-carmine test. Add a solution of indigo carmine to color 

 sugar solution distinctly blue, and add solution of sodium carbonate, and 

 heat. The blue color changes to purple and then to brown and yellow,, 

 but is restored on shaking the solution. 



(vii.) Phenyl hydrazine test. A solution of phenyl hydrazine hy- 

 drochloride and sodium acetate is added. Keep in water-bath at boiling 

 for some minutes, then cool. Yellow crystals result. 



Quantitative Estimation of Grape Sugar. 



1. Fehling's Method. Solution required = copper sulphate and caus- 

 tic soda, with some sodic potassic tartrate of such a strength that 10 c.c. 

 of solution contain the amount of cupric oxide which 0.5 grm. of sugar 

 can reduce to cuprous oxide. (This solution should be freshly pre- 

 pared.) It is made as follows: Take of sulphate of copper, 40 grms. ; 

 neutral tartrate of potash, 160 grms.; caustic soda (sp. gr. 1.12), 750 

 grms.; add distilled water to 1154.5 c.c. Each 10 c.c. contains .05 grm. 

 of sugar. 



Method. .Take 10 c.c. of the saccharine solution free from albumen, 

 and add 90 c.c. of distilled water. Place this in a burette. Put into a 

 flask or dish 10 c.c. of the standard solution, and dilute with four times 

 its bulk of water and boil. Run into it, from burette, some of the 

 diluted urine, say 20 c.c., and boil. Allow precipitate to settle, and if 

 supernatant fluid is still blue, add, say, 5 c.c. from burette, and boil 

 again, and so on, till the fluid ceases to have a blue tinge, taking care, 

 toward the end of the process, to add only a few drops each time. If, 

 after adding 20 c.c. of diluted urine and boiling, the fluid has been 

 decolorized, too much of the solution has been added, and another esti- 

 mation with a second 10 c.c. of standard solution must be made, but 

 less than 20 c.c. of the saccharine solution should be added (say 10 c.c.) 

 in first instance. 



When the number of c.c. of diluted urine required to decolorize the 

 solution has been determined, that volume contains the amount of sugar 

 necessary to reduce 10 c.c. of standard solution, i.e., .05 grm. But one- 

 tenth only of this is the saccharine solution, /. one-tenth of number of 

 c.c. used contains .05 grm. of sugar. From this, the percentage can be 

 easily calculated. 



2. Pavy's Modification of Fehling's Method. By Fehling's method it 

 is difficult and tedious to judge of the point of complete reduction of 

 the cupric oxide. Dr. Pavy, accordingly, uses a strongly ammoniacnl 

 solution of the above. A certain amount is introduced into a small 



