80 PRACTICAL AGRICULTURAL CHEMISTRY [265 



Note i. — The solid (NH,) z C0 M is dissolved in cold water, but in 

 diluting, one-fourth of the * Winchester' must be filled with 3trong 

 NH 4 HO. 



Note 2.— This reagent undergoes decomposition by exposure to 

 light, and must not be kept near a window : it is better to dissolve a 

 fragment of the solid each time it is required. 



265.— Chemicals required for Sections I. and II. 



With the exception of the bench reagents the whole of the sub- 

 stances required for these sections are enumerated below : — 



Note 1. — Dissolve 33 grams of KI and 13 grams of HgCl 2 in 

 800 c.c. of water, add strong HgCl 2 solution antil a faint permanent 

 precipitate is formed, then add 160 grams of solid KHO. Allow to 

 cool and make up to one litre with water. Use the clow supernatant 

 liquid. 



