BO PHYSIOLOGY OF NUTRITION. 



28. Food Stuffs in Water. 



It is of interest to determine the presence in water of some 

 substances which, are of importance as plant food, taking for 

 examination, river, pond, or spring water. We acidify 20 c.c. of 

 water with a few drops of Hydrochloric acid, add Barium chloride 

 solution ; turbidity or precipitate indicates the presence of sul- 

 phate. Acidify 20 c.c. of the water with pure HN0 3 and add 

 Silver nitrate solution ; a white curdy precipitate indicates the 

 presence of chloride. 50 c.c. of the water are acidified with 

 Hydrochloric acid, excess of ammonia is added and lastly 

 Ammonium oxalate ; a white precipitate indicates the presence 

 of Calcium. Lime occurs in water in combination with Sulphuric 

 acid or with Carbonic acid (Calcium bicarbonate). The presence 

 of this latter compound is detected by heating the fresh water, 

 since it is easily decomposed on heating into the normal Calcium 

 carbonate, which separates out, rendering the fluid turbid, and 

 Carbon dioxide. If spring water, fairly rich in Calcium bicar- 

 bonate, is laid aside for some time in a small glass at the ordinary 

 temperature, crystals of normal Calcium carbonate separate out, 

 whose form we can easily make out by microscopic examination. 



Since we do not here propose to give an introduction to the 

 examination of water, but only to establish the fact that water 

 contains food stuffs, we will now leave the subject. It has, how- 

 ever, already been indicated in another place how to proceed in 

 examining water for ammonia and Nitric acid. 1 



1 For an exact account of the method of water examination, sec Tiemann, 

 Anleitung zur Untermchung von Wasser, 1874, and Keichardt, Grundlagen zur 

 Beurtheilung des Trinkivassers, 1880. 



29. Ash Analysis. 



Although qualitative and quantitative ash analyses are some- 

 what troublesome and tedious, I strongly advise any one who 

 intends to occupy himself with physiological studies to carry out 

 researches of this kind. The plant material is first carefully 

 cleansed, being freed, e.g. from adhering dust. Fresh roots must 

 then be cut up into slices, which, as also fresh stems and leaves, 

 are hung up in the drying chamber at a temperature of about 

 50 C. to dry. The dried roots are pounded up to a moderately 

 fine powder; the dried stems or leaves are cut up with scissors. 

 Air-dry seeds are to be pounded to a coarse powder in a mortar. 



Suppose it is desired to investigate the ash of the aerial parts 



