42 HYDROCYANIC-ACID GAS FUMIGATION IN 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 definiteness under the 

 same conditions; that is, given the same conditions, when one 

 chemical acts upon another in the production of a third substance, 



