REAGENTS. 21 



kept in a cool place in the dark, and in completely filled, well- 

 closed bottles (Hoppe-Seyler). 



The solution (6) may be prepared, and kept for adding to (a ) 

 freshly prepared when required. 



Before using a kept solution to test for sugar, always boil a 

 little of it by itself to see if any reduction will take place. 



From 1 c.c. of this solution the copper is completely reduced 

 by '005 grm. of grape-sugar. 



Y. Organic substances. 



Alcohol. Used as a solvent for various substances, 

 such as fats, oils, resins, colouring-matters, &c., and as a 

 precipitant for various substances. It has a peculiar 

 action upon some proteid crystalloids. 



Ether. Used as a solvent for wax, fats, resins, &c. 



Cane sugar. The concentrated aqueous solution 

 is used, together with strong sulphuric acid, as a test 

 for proteids. A dilute (1 per cent.) solution is useful 

 for mounting living cells for observation under the 

 microscope. 



Alkanet. The alcoholic extract, or better, an alco- 

 holic solution of alkannin, is used as a test for resin and 

 caoutchouc : a fresh solution must be prepared on each 

 occasion. 



Phloroglucin. Used in alcoholic or aqueous solu- 

 tion as a test for lignin. The section is first treated 

 with hydrochloric acid and then with solution of phloro- 

 glucin : the lignified cell- walls assume a bright red 

 colour. 



If phloroglucin cannot be obtained, it may be replaced by an 

 extract of cherry wood. Shavings of young cherry- branches are 

 extracted with alcohol for twenty-four hours to remove chlorophyll 

 and other substances ; then the alcohol is poured off. The shavings, 

 after being pressed, are extracted for several days with alcohol, 



