Materials and Formulas. 151 



sides of the canvas should be painted, and the dressing well 

 rubbed into the fiber with a flat paint-brush. If oil is used, 

 the canvas should be spread out and thoroughly dried before, it 

 is rolled up, or it is liable to be destroyed by spontaneous com- 

 bustion. When dry there is no danger from this." 1 



IRON CHLORIDE (probably FERROUS CHLORIDE, FECL 2 ). 

 This material has been successfully used in checking certain 

 coffee diseases, and its use appears to be restricted almost 

 entirely to this plant. Very dilute solutions were applied, and 

 these proved to be exceedingly adhesive. The remedy is at 

 present little known. 



IRON SULPHATE ; COPPERAS ; GREEN VITRIOL ; FESO 4 . 

 Copperas is formed by the union of sulphuric acid and iron. 

 It is a green crystalline substance, and when finely broken up it 

 bears a certain resemblance to granulated copper sulphate, and 

 as it is much cheaper than the latter, it has been used as a 

 means of adulterating the copper salt. Iron sulphate dissolves 

 readily in water. The ferrocyanide of potassium may be used 

 as a means of detecting the presence of this compound. This 

 test gives a reddish-brown precipitate with a concentrated solu- 

 tion of copper sulphate, but with a dilute solution it merely 

 gives the same color to the liquid, without the formation of a 

 precipitate. With the sulphate of iron, the test forms a deep 

 blue precipitate, very easily distinguished. If there is any ques- 

 tion as to the purity of copper sulphate, this test may easily be 

 used and the adulteration detected, provided the sulphate of 

 iron has been used as an adulterant. 



Iron sulphate is of no practical value as an insecticide, and 

 its use as a fungicide is very limited. Iron is not nearly so 

 efficient in this respect as copper is, so the latter is almost 

 invariably preferred except when the plants to be treated are 

 dormant. The iron salt may then be used as follows : 



Iron sulphate 4-8 pounds. 



Water 1 gallon. 



All parts should be thoroughly treated with this solution ; 

 but the value of the operation has, in most cases, still to be 

 determined. 



i Craw, California State Ed. of Hart. 1894, Bull. 68, 20. 



