REMOVAL OF SPRAY RESIDUE FROM APPLES AND PEARS 19 



fruit, and constant care must be exercised to keep the cleaning 

 solution at proper strength. 



Where difficulty has been experienced in cleaning fruit, contin- 

 uing its exposure to the washing treatment much longer than was 

 the common practice in 1927 did not result in any marked improve- 

 ment, although there was some increase in efficiency. In some cases 

 soaking the fruit in the solution may result in slightly improved 

 removal of the residue, owing to mechanical loosening of dust and 

 residue particles, but the chemical reaction between hydrochloric 

 acid and lead arsenate probably takes place very rapidly, as hereto- 

 fore mentioned, and to prolong the exposure does not proportionately 

 increase the reaction. 



The proper washing of apples generally requires an acid concen- 

 tration of at least 1 gallon to 100 gallons of water, although lightly 

 sprayed apples and pears may often be satisfactorily cleaned with 

 slightly less. With fruit that was difficult to clean, an increase in 

 concentration up to 6 gallons of acid to 100 gallons of water resulted 

 in increased cleaning efficiency, but the increases in efficiency have 

 been proportionately less for each gallon added. Above 4 gallons to 

 100 the increase in efficiency has been relatively small. The use of 

 high acid concentration is more costly, puts a greater burden on 

 the rinsing section, and increases the danger of injury to the fruit 

 from acid burning as well as from soluble arsenic due to the con- 

 tinued solvent action of the acid on poorly rinsed fruit. It should 

 be possible to clean the general average of fruit soon after picking, 

 in suitable equipment, with an acid concentration of not more than 

 3 gallons of acid to 100 gallons of water. 



The acid strength should be watched carefully during the washing 

 operation by means of the simple titration method described on page 

 11 of this circular. That is particularly true if wet fruit is put 

 through the machine or if fruit is washed which has been sprayed 

 with Bordeaux mixture or lime together with lead arsenate. A cer- 

 tain proportion of acid solution is carried away on the fruit as it 

 passes through the washer. This loss should be replenished from 

 time to time from a storage barrel of cleaning solution arranged to 

 stand beside or over the washer. The acid tank of any washing 

 machine should be emptied at least once a day. If tanks of the cus- 

 tomary dimensions are used, the accumulation of soluble arsenic in 

 the cleaning solution in one day's time will not be sufficient to interfere 

 with the cleaning operation or unduly contaminate the rinsing section. 



Certain precautions should be followed in the use of commercial- 

 grade hydrochloric acid (also commonly called muriatic acid). It is 

 usually shipped in glass carboys holding about 10 gallons of con- 

 centrated acid. The acid should test 20° Baume, which is equivalent 

 to about 32.1 per cent. A slight yellow tinge in the acid does not 

 detract from its value as a cleaning agent. 



Care should be exercised in handling the acid, since it will attack 

 metal, cloth, and leather, unless neutralized by soda or lime. Either 

 hydrated lime, carbonate of lime, or common baking soda will be 

 satisfactory for neutralizing. 



Some form of a carboy tipping frame will be found convenient as 

 an aid in pouring the acid from the container.' A nonmetallic gallon 

 measure with quart divisions is a necessary utensil for properly 

 measuring the required concentrated acid. 



