254 LETTER-FILES OF S. W. JOHNSON 



vague, but I gather that one part of benzoic acid or sodium 

 benzoate by weight will be ordinarily sufficient for 500 to 1000 

 parts by weight of fruit. 



The pineapple contains a powerful digestive agent, hrome- 

 lin, which Professor Chittenden has investigated, and which 

 is doubtless a principal reason of the salutary quality of that 

 fruit. This vegetable-pepsin is destroyed by a boiling heat, 

 and therefore it is desirable to preserve the pineapple un- 

 cooked. Benzoic acid, I believe, does not in the least impair 

 the digestive power of bromelin. 



I should suppose that the sliced or shredded pineapple, 

 sprinkled with a little sugar and with the benzoate, and put 

 into bottles closed with clean corks or into fruit- jars, would 

 ordinarily keep without further trouble. I say ordinarily, 

 because of the microbes (fungi, bacteria and what not) which 

 occasion the moulding, fermentation or putrefaction of fruits, 

 the name is legion, and some are vastly more hard to kill or 

 suppress than others. It may happen, therefore, that a pro- 

 portion of benzoic acid which will answer for this year, or 

 in this place, or with the pineapples now in market, will be 

 insufficient next year or elsewhere, because of a difference 

 in the bacterial seeding or inoculation. 



It is important that each jar of fruit should receive its 

 proper amount of benzoate. I should advise either to have 

 weighed out (by the druggist) and placed in each jar, just 

 the dose needed and add to each the amount of granulated 

 sugar required for sweetening, or, if a considerable batch of 

 fruit is treated at once with a single dose of benzoate, I should 

 sweeten to taste with dry sugar, and keep the whole some 

 days in one large well-covered vessel until the fruit has yielded 

 a goodly amount of juice and has thereby become impreg- 

 nated with the preservative. The former plan is preferable 

 since it is desirable to avoid exposing the fruit unnecessarily 

 to seeding with the bacterial germs wherewith air is commonly 

 loaded. Yours very truly, S. W. Johnson. 



