120 



PUBLIC HEALTH CHEMISTRY 



of lemon juice per head per day must be issued when a 

 vessel has been ten days at sea, except when in harbour 

 if fresh vegetables can be had. 



Lime Juice Is the expressed juice of the Citrus 

 limetta. Like lemon juice, it contains free citric acid, 

 traces of other organic acids, citrates, sugar, and albuminous 

 and mucilaginous bodies. The average composition of 

 these juices is : 



Lemon Juice 

 Lime Juice 



Total 

 Solids 



Sugar 



8-8o%j2- 3 o% 

 8-6 4 % 070% 



Citric Mineral , 

 Acid Matter Potash PO a (sol.) 



4'57 % 

 5*6o% 



0'35 % 

 o*35 % 



0-15 % 



0-12 % 



O'OIO % 



0-065 % 



According to the above standards, the percentage of citric 

 acid should be 6-6 to 8-8 per cent. Few juices reach the 

 higher figure. The important points in the analysis are : 

 specific gravity, total solids, free citric acid, combined 

 acidity, ash, free mineral acid, tartaric acid, alcohol, 

 sulphites, and salicylic acid. 



Specific Gravity. Lime juice is usually about 1035 to 

 10 37 (= 3 2 grains per oz.). 



Total Solids. Evaporate 10 c.c. over water-bath, and 

 dry in oven to constant weight. Vary from 5 to 9 per cent. 



Ash. Ignite the residue. For lemon juice, should not 

 exceed 3 per cent, and be neutral. 



Free Citric Acid. Titrate 20 c.c. with N/i or N/2 

 NaOH, using phenolphthalein as indicator. 1 c.c. N/i 

 NaOH s=s 0-07 grm. crystallized citric acid, H 3 C 6 H.0 7 .H 7 0. 

 The percentage X 4*375 = grains per fl. oz. Varies from 

 5 to 9 per cent. 



Combined Acids. The neutralized juice from the above 

 process is evaporated to dryness on the water-bath, and 

 the residue ignited at a low temperature. The citrates 

 are changed to carbonates. Cool, and extract mass with 

 hot water, add sufficient N/i sulphuric acid to make acid 

 (noting the quantity), boil to get rid of C0 2 and then 

 filter. Now titrate with N/i NaOH, using methyl-orange 

 as indicator, to estimate amount of N /i sulphuric, added 

 in excess. This amount deducted from the total amount 



