42 HYDROCYANIC-ACID GAS FUMIGATION IX CALIFORNIA. 
taining large quantities of sulphate of iron should be avoided for 
the same reasons that cyanid containing large quantities of impu- 
rities should be avoided, even though the impurities are apparently 
harmless. 
Traces of nitric acid (HN0 3 ) are sometimes present in sulphuric 
acid. For several years an opinion has been current in California 
that nitric acid when present in sulphuric acid used in fumigation 
would result in the burning of fruit. Burning of fruit has occurred 
to a greater or less extent throughout the history of fumigation, 
yet in recent years, because this damage has sometimes taken place 
when an acid made from pyrites was being used, and in which a 
trace of nitric acid was sometimes present, the belief has become 
quite general among fumigators that such an acid was unsafe. 
The theory proposed as the cause was that the heat produced in 
generating the hydrocyanic-acid gas drove off the nitric acid in the 
form of a vapor, which, coming in contact with the cooler surface of 
the fruit, condensed, resulting in a burn or pit. Careful experiments 
were recently carried out in order to decide this point. Eight orange 
and lemon trees well laden with fruit were treated on three different 
nights, using sulphuric acid containing from 1 to 10 per cent of pure 
nitric acid. Dosage schedule No. 1 was followed. The exposure 
was one hour. No pitting or burning resulted with any of the 
strengths used. As these amounts of nitric acid are far in excess of 
the quantities ever found in commercial sulphuric acid it can be 
safely concluded that there is no danger of burning as a result of 
the presence of nitric acid in the commercial sulphuric acid. 
Traces of arsenic, lead, or zinc are sometimes found in commercial 
sulphuric acid, yet in all samples of acid analyzed during this inves- 
tigation the quantity, when present, has been so small as to demand 
no consideration as a source of injury. 
Sulphuric acid is purchased largely in iron drums containing from 
1,500 to 2,000 pounds. Glass carboys of about 10'gallons' capacity 
are sometimes used. The drums, because of their great weight, are 
seldom taken into the field. A common and convenient method 
is to roll the drums onto an elevated platform at the source of sup- 
plies. The acid is then removed into glass carboys or some other 
receptacle for carriage into the field. Two or three carboys usually 
will contain enough acid for one night's run of an outfit of tents. 
Care should be observed in handling this acid. Rubber gloves 
are advisable. If some acid accidentally reaches the flesh hasten to 
wash the affected parts with water. 
THE AMOUNT OF SULPHURIC ACID NECESSARY. 
Chemical combinations take place with defmiteness under the 
same conditions; that is, given the same conditions, when one 
chemical acts upon another in the production of a third substance, 
