FUMIGATION OF CITRUS TREES. 41 
fact u re 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. 
No 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 (lI 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 of 
chemicals is also different. A 1-1^-2 formula is advised; that is, to each ounce (average) of 126-130 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. 
