CALIFORNIA CITRUS CULTURE. 77 



All less than half ounces are placed in the lower figure, while half 

 ounces or over are placed in the next higher figure. A more convenient 

 way of fixing up the schedule is to have a cylinder made of zinc, with 

 a narrow slot, the width of a row of figures, covered by a glass, and a 

 wooden roller on the inside, similar to a rolling pin. Each end of the 

 cylinder is closed by a cap with a hole in the center, in which turns 

 the handles of the wooden roller. The chart or schedule is attached 

 to the roller so as to revolve in the cylinder. The figures of the distances 

 around are pasted along the top of the slot to conform with the like 

 numbers on the schedule. In finding the dosage one has only to turn 

 the roller until the distance over shows at the left-hand end of the slot ; 

 the figure at the top of the slot shows the distance around. In this way, 

 the chart is kept perfectly dry and bright and the possibilities of making 

 a mistake are reduced to a minimum. This arrangement was first 

 invented by Mr. C. E. McFadden, Fullerton, California, who used it 

 on all of his chemical carts. 



MISCELLANEOUS EQUIPMENT. 



Rubber gloves for handling the acid graduate and generators, pure 

 rubber tubing for drawing off the acid, acid clamps or cut-offs to control 

 the flow, a pair of scales registering ounces, thermometer and good 

 lights are as necessary as any of the other equipment. 



CHEMICALS. 



The chemicals used for generating hydrocyanic acid gas in fumigat- 

 ing work are potassium or sodium cyanide, commercial sulphuric acid 

 and water. The cyanide is usually handled in the 200-pound cases and 

 the acid in steel drums weighing from 1,200 to 2,000 pounds. 



Cyanide. For many years potassium cyanide 98-99 per cent pure 

 was thought to be the best and only reliable source of hydrocyanic acid 

 gas. It was formerly used to the exclusion of all others, and is still 

 preferred by many who do not wish to add the injurious residue of 

 sodium cyanide to their soil, and also by those who do not see enough 

 advantages in sodium cyanide to warrant a change. 



There are two grades of sodium cyanide: the 98-100 per cent pure, 

 which is totally unfit for fumigation purposes because of the impurities 

 it contains, and the pure 129-130 per cent sodium cyanide, which is used 

 almost exclusively for fumigation work. This product, though some- 

 what more expensive than the potasisum cyanide per pound, has much 

 more available hydrocyanic acid gas and consequently a smaller amount 

 is necessary, which is enough smaller to make the cost of dosage less 

 than that for potassium cyanide, and is therefore fast displacing it. 

 Much has been said for and against the sodium cyanide relative to the 

 burning of fruit and foliage, but this is still an unsettled point. 



