I. INTRODUCTION 13 



Fluorine occurs mainly as calcium fluoride, CaF.,, in the mineral 

 known as fluor-spar. It is also present in almost all naturally oc- 

 curring forms of calcium phosphate, and doubtless, in quantities too 

 small to be readily detected, in many other minerals. The element 

 itself is difficult to prepare owing to its great chemical activity. 



It is found in combination in the bones, blood and urine of animals. 

 Bone-ash contains about 4 per cent of calcium fluoride, while many 

 mineral phosphates contain as much as 7 or 8 per cent. According to 

 Lorenz, the evolution of hydrofluoric acid by a phosphate on treat- 

 ment with sulphuric acid may be taken as a proof that a mineral 

 phosphate is present. This test is not entirely satisfactory, since 

 many mineral phosphates do not give it, indeed they are known 

 to contain practically no fluoride, but chloride. Thus, there are two 

 varieties of apatite corresponding to the formulae 3Ca 3 P,,O 8 .CaF 2 and 

 3Ca 3 P 2 8 .CaCl 2 , and many specimens have a composition intermediate 

 between those expressed by the above formulae. Of course the chloride 

 variety is preferable for the manufacture of superphosphate. 



Applications of calcium fluoride to the soil have been found, by a 

 Japanese investigator, 1 to have a beneficial effect upon some crops. 



ELEMENTS OF MINOR IMPORTANCE. 



Boron always occurs in combination as boric acid (HB0 2 or 

 H 3 B0 3 ) or berates. It is not a very abundant element except in a few 

 localities, e.g., in Tuscany and in California, but of recent years its 

 presence in a number of plants and products from plants, particularly 

 in wines and the leaves, stalks, etc., of the vine, has been detected by 

 various observers, leading to the conclusion that boric acid must be 

 present in many soils, which probably derive it from igneous rocks. 



There is no evidence that it is essential to plant life. Boric acid or 

 boracic acid is possessed of considerable anti- putrefactive properties 

 and is often used for preserving milk and other food products. 



Iodine. This element is comparatively rare in nature, being found 

 in extremely small quantities in sea-water and in certain mineral 

 waters. It also occurs in caliche the crude nitrate of soda of Peru 

 and Chili in the form of sodium iodate, NaIO 3 . In the organic king- 

 dom it occurs in the thyroid gland of man and many animals and in 

 certain seaweeds, especially in Laminaria digitata and L. stenopliylla, 

 where it amounts to nearly 0'5 per cent of the plant. Its presence in 

 terrestrial plants is rarely observed, but Uchiyama 2 found that from 

 the application of small quantities of potassium iodide 124 grammes 

 per hectare an increased yield of certain crops was obtained. This 

 may have some bearing on the use of seaweed as a manure. 



Manganese resembles iron in most of its properties. It is always 

 found in union with other elements, often with oxygen, e.g., as pyrolu- 

 site, Mn0 2 , psilomelane, BaO. 2MnO 2 . It is apparently not essential 



l. Coll. Agr., Tokyo, 1906, 7, 85. 

 2 Bull. Imp. Centr. Agric. Exp. Stat., Japan, 1906, 1, 35. 



