FUMIGATION OF CITRUS TREES. 41 



fact lire as suitable a grade of fumigating cyanid in this country as in 

 Germany. Such a belief is, of course, erroneous. Chemical analysis 

 of this so-called " American" cyanid has shown it to be not potas- 

 sium cyanid but sodium cyanid, which is a very different article. 

 Xo potassium cyanid is manufactured in this country. 



A potassium cyanid x guaranteed to be 98-99 per cent pure should 

 be used, as experience gained during this investigation, as well as 

 that from commercial operations, has proved this grade of cyanid 

 to be uniformly successful. Moreover, such a high-grade article is 

 quite free of sodium chlorid (common salt), the detrimental action 

 of which is explained later. 



Cyanid should be exposed to damp air as little as possible, as it is 

 decomposed by moisture. Analysis of a sample exposed to the air 

 for a few months showed it to be several per cent less pure than 

 originally. Such a cyanid, or even one which has become moistened 

 by only a few days' exposure to the weather, is slower in generating 

 its gas, and this is an objectionable feature in fumigation. After 

 opening in the field, the case of cyanid should be protected by a tight 

 cover which will ward off the action of dew or rain. 



SULPHURIC ACID (h 2 S0 4 ). 



A commercial sulphuric acid (H 2 S0 4 ), 66° Baume, which is approxi- 

 mately 93 per cent pure, should be used. Sulphur is the basic 

 ingredient in the manufacture of sulphuric acid. Generally speaking, 

 an acid in which the sulphur is obtained from brimstone is preferable 

 to one made from iron pyrites. The reason is that those which are 

 made from a brimstone base usually contain fewer impurities than 

 those made from iron pyrites. If the impurities be eliminated, 

 however, the sulphuric acid made from the one is as satisfactory in 

 fumigation as that made from the other. 



The commonest impurity in sulphuric acid is sulphate of iron 

 (FeS0 4 ). This often occurs in acids made from pyrites, and some- 

 times to a very great extent. It adds a milky appearance to the 

 acid. The action of acid on long-used iron drums also causes the 

 formation of sulphate of iron, evidenced by' the whitish appearance 

 of the " settlings" or the acid at the bottom of the drum. The 

 writer has used acid containing considerable sulphate of iron without 

 any apparent injury to citrus trees or fruit. Nevertheless acid con- 



1 Experimentation during this investigation has shown that a high grade of sodium cyanid will produce 

 exactly as satisfactory results as a high-grade potassium cyanid. No sodium cyanid less than 126-130 per 

 cent pure (as reckoned in terms of a potassium cyanid) should be used. If a suitable potassium cyanid is 

 not available then purchase a sodium cyanid of the purity mentioned. A pound of this sodium cyanid 

 contains approximately one-fourth more available gas than a pound of potassium cyanid. Hence, if used, 

 the dosages employed should be one-fourth less than those mentioned in this bulletin. The proportion ol 

 chemicals is also different. A 1-1J-2 formula is advised; that is, to each ounce (average) of 12(V130 per 

 cent sodium cyanid use 1} ounces (liquid measure) of sulphuric acid and 2 ounces of water. 



For a thorough treatment of sodium cyanid in relation to fumigation see Part II of this Bulletin. 



