94 HYDROCYANIC-ACID GAS FUMIGATION IN CALIFORNIA. 



As sodium has a lower atomic weight than potassium, a greater 

 yield of gas is obtained from the same weight of the cyanid of the 

 former and a larger amount of sulphuric acid is required for its 

 decomposition. According to this reaction, 1 ounce (avoirdupois) 

 of sodium cyanid requires 1 ounce (avoirdupois) of sulphuric acid, 

 H 2 S0 4 , or 1.07 ounces of commercial sulphuric acid containing 93 

 per cent of sulphuric acid, which is equivalent to 0.56 fluid ounce. 

 As before noted, to get the best yield of gas the sulphuric acid must 

 be in considerable excess, when the reaction would be : 



NaCN + H 2 S0 4 = NaHS0 4 + HCN, 



or for each ounce of sodium cyanid there would be required 2.14 

 ounces (avoirdupois) of 93 per cent sulphuric acid, equivalent to 1.12 

 fluid ounces. To determine the best proportions of sodium cyanid, 

 sulphuric acid, and water to use in actual practice in order to obtain 

 the largest yield of gas, the following experiments were carried out, 

 using pure sodium cyanid containing 94 per cent actual sodium 

 cyanid, the remainder being mainly moisture, and commercial sul- 

 phuric acid "66° Baume," which on analysis showed 93.52 per cent 

 sulphuric acid. Three-ounce (avoirdupois) portions of the sodium 

 cyanid were employed in each experiment and varying amounts of 

 sulphuric acid and water were taken. The decomposition was car- 

 ried out in tall beakers of 4-liter capacity in order to prevent any 

 possibility of loss from spattering. The water was first measured 

 into the beaker, then the acid added, and the weighed package of cyanid 

 was immediately dropped in. After standing 40 minutes the residue 

 was washed out of the beaker into a graduated flask, cooled, made up 

 to mark, thoroughly mixed, and aliquots taken for the determination 

 of the amount of hydrocyanic acid remaining in solution. As has 

 been shown by experiments herein reported, the difference between 

 the total amount of cyanid in the quantity of material taken and 

 that remaining in the residue does not represent correctly the amount 

 of gas given off and available for fumigating purposes, but when 

 operating on a pure cyanid, the less hydrocyanic acid remaining in 

 the solution the greater will be the yield, and for measuring the rela- 

 tive efficiency of the different mixtures of acid and water it is only 

 necessary to determine the amount of hydrocyanic acid in the residue. 

 In all determinations of cyanid Liebig's 1 method has been used. 

 In every case where ammonia was present in the solution, due to 

 previous decomposition of the cyanid (in which case the end reaction 

 would not appear as soon as it should^ due to the solvent action of 

 ammonia on the silver cyanid), a few drops of a dilute solution of 

 potassium iodid were added in order to overcome this source of error, 

 silver iodid being insoluble in dilute ammonia. 



1 Volumetric Analysis, Sutton, 9th ed. rev., p. 200. 



