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CHAPTEE XVI. 

 MISCELLANEOUS PRODUCTS USED IN AGRICULTURE. 



IN this chapter, which is necessarily disconnected and frag- 

 mentary, such substances as find applications in agriculture 

 are briefly described from their chemical aspect, while some 

 reference is made, in most cases, to the manner and proportion 

 in which they are used. An alphabetical arrangement has been 

 adopted, since the matters to be dealt with are so numerous 

 and diverse that any connected or continuous description w T ould 

 be impossible. In some cases the substances mentioned have 

 already received notice in the preceding chapters ; when this 

 is the case, reference to the place is given, so as to avoid 

 unnecessary repetition. 



Arsenious Oxide, As 4 (i (in the state of vapour). This 

 substance is known in three distinct forms, viz., one amor- 

 phous or vitreous and two crystalline regular octahedra and 

 trimetric prisms. Ordinary white arsenic consists mainly of 

 the powdered vitreous variety, which, however, tends to pass 

 into the heavier, octahedral form. The specific gravities 

 of the vitreous and octahedral varieties are about 3' 7 and 4-0 

 respectively. Their solubilities in water vary with circum- 

 stances. If water be shaken for a long time at 15 with the 

 solids the amounts dissolved by 100 parts of water are 0'28 of 

 the crystalline and 0*92 of the vitreous varieties, while if satu- 

 rated solutions at 100 be cooled to 15, 2*18 of the crystalline 

 and 3*33 of the vitreous form remain in solution. 



Arsenious oxide dissolves readily in solutions of caustic 

 alkalies or of alkaline carbonates, arsenites of the alkali metals 

 being formed. "Fowler's solution" contains potassium ar- 

 senite. Arsenious acid, as the oxide is often called, and its 

 compounds, are powerful poisons both to animals and plants, 

 but curiously have much less influence upon micro-organisms. 

 Indeed certain moulds can develop in the presence of 



